RISK FACTORS FOR HEARING LOSS IN ADOLESCENTS

Valerie Ann Phelan

A thesis submitted in confonnity with the requirements

for the degree of Master of Science

Graduate Department of Public Health Sciences

University of Toronto

OCopyrîght by Valerie Ann Pheian 200 1

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RISK FACTORS FOR HEARING LOSS IN ADOLESCENTS

Master of Science 200 1

Valerie Ann Phelan

Graduate Department of Public Health Sciences

University of Toronto

ABSTRACT

Many studies have shown that hearing in young adults today has

worsened compared to standards (such as ISO 7029) and previously

published studies. The exact reasons for this observed decline in

hearing remains unknown. The purpose of this study was to determine

absolute hearing thresholds in adolescents and collect information

regarding possible risk factors for hearing loss. Pure-tone

audiometric thresholds were measured at nine different frequencies

from 0.25 to 10 kHz in each ear. Additionally, consonant recognition

was assessed using the Four Alternative Auditory Feature (FAAF) test

in quiet and in speech-spectrum noise. Hearing thresholds in the

present study were compared to results from published studies in

teenage subjects and young adults. Results from the FAAF test did not

reveal any signs of hearing loss and no conclusive evidence was found

to suggest hearing acuity in adolescents is better than in young

adults in the conventional frequency range (0.25 to 8 kHz).

1 am indebted to many individuals who provided me with assistance and encouragement over

the course of this study, including:

Dn. Sharon M. Abel and Andrea Sass-Kortsak for giving me the opportunity, financial

support, encouragement, loads of valuable advice, and for having dedicated so much of

their tirne throughout this project.

My fnends Jean, Penelope, Christine, Jérôme, Mike, Nat and other colleagues at the

University of Toronto for their support and understanding.

The schools fiom the Toronto Catholic and District Schools boards whom so graciously

provided access to the students that gladly participated in the study.

1 especially want to thank my parents and grandparents for their continua1 love and support,

both morally and financially.

DEDICATION

in loving memory of

M s . Denise Beauce Matte

TABLE OF CONTENTS

ABSTRACT

ACKNOWLEDGErnNTS

DEDICATION

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF APPENDICES

ii

iii

iv

v

Ur

xii

xiii

........... CHAPTER 1 : INTRODUCTION .... .............. ................................... 1

............... 1.1 Hearing Acuity in Teenagers and Young Adults .........m....... 2

1.2 Study Objectives ...................................................m................................. 3

........................................................... CHAPTER 2: LITERATURE REVIEW 4

2.1 Noise and Hearing .................................................................................. 4

2.1.1 The Auditory Apparatus ....................................................................... 4

............................................................................................... 2.1.1.1 The outer and middle ear 4

2.1.1.2 The inner ear ................................................................................................................... 5

2.1.1.3 Hearing and the organ of Corti ...................................................................................... 6

2.1.1.4 The cochlea's energy supply .......................................................................................... 9

....................... .......... 2.1.2 Temporary and Permanent Threshold Shi& ....... 9

............... 2.1.2.1 Underlying Mechanisms of Tempora y and Permanent Thmbold Shift 10

........................................................................................................................ 2.1.2.2 Summary 15

v

2.1.3 Types of hearing loss (Conductive vs Seflsorined) ........................ 16

2.2 Noise-lnduced Hearing Loss: From The Womb To Early

Adulthood ............................. ..... ......................................................... 17

2.2.1 Fœtal Noise Exposures ...................................................................... 17

................................ 2.2.2 Noise Exposures from To ys During Childhood -20

2.2.3 Noisy Hobbies and Hearing Loss in Young Adults ........................... 22

........... 2.3 Otitis Media ..................m......o......o.........m..........m.............. ..24

2.4 Other Sources of Hearing Loss .... .......................m.....o...m...m....m..m.... 25

Consequences of illness .................................................................... 25

............................................................................................... Drugs -26

Physical barriers ................................................................................ 28

Age ................................................................................................... 28

.............................................................................................. Gender 28

Low birth weight ............................................................................... 29

........................................................................................... Genetics -29

3.1 Study Desig n .................................................................................... 37

3.2 Surveys .............................................................................................. 38

3.3 Apparatus .....e...........m.~................~.o..~m...om~.m...m...mo.om...o~m~..m....o o.mmom.oo39

........................................................................... 3.4 Audiometrie T d n g 40

3.4.1 Hearing Thresholds .......................................................................... 40

3 .4.2 Consonant Discrimination ................................................................ 41

3.5 Appmach to Data Reduction and SCitistical Analysis ................... .41

.................................................................................. 4.2 Survey Findings 46

4.2.1 Screening Questionnaire .................................................................... 46

4.2.1.1 Information about Mothen . . . . ~ . . ~ . . . . . ~ . ~ ~ . ~ . ~ ~ ~ ~ ~ o o . ~ ~ ~ . ~ ~ ~ m ~ ~ ~ ~ ~ ~ o . ~ ~ . ~ . . . ~ 48

4.2.1.2 Information About the Studcnts .............................................................................. 54

4.2.2 Detailed Questionnaire ...................................................................... 56

4.2.2.1 Health Information .....................a............................................................................. 56

4.2.2.2 Mother's Workplace Noise ..,....,........o.w...............o.........œ.....wm................w............w.. . 61

4.2.2.3 Récreational Noise Sources ............................................~......................................... 65

........................................................... 4.2.204 Drugs. Alcohol. and Tobacco Consumption 68

...................................................................... 4.3 Psychoacoustic Resulh .71

........................................................................... 4.3.1 Hearing Thresholds 71

4.3.2 Consonant Discrimination ................................................................. 75

4.3.3 Correlations ....................................................................................... 79

4.3.3.1 FAAF and Thrcshold Correlations .......................................................................... 79

4.3.3.2 FAAF and Questionnaire Data Comlations ........................................................... 79

vii

4.3.4 Effects of otitis media on hearing thresholds and FAAF scores

m norse.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

5.1 Hearing levels w e o e w e w e e e w w w w w w ~ w e w w m w e w e w e w w w w w w w w w w e e e o w o w w w w w w w e w w w w w w w e w w m e w w w m w w w w e w e e w w w e m e ~ ~ ~ 85

5.1.1 Hearing in teenagers compared to hearing in young adults . . . .. . .. . .. .. ... 89

5.2 Spcech understanding in noise w e e w e w w w e e e e w w e e w m w w w w w w w w e e w e w e e w w w w e w w e e w e w e e w w e w e a . w w w w 91

5.3 Potential Sources of Hearing Loss in Teenagers and Young

A d ~ l t S ~ w w e w e w w w e e w e w w w w e w w e e e w w ~ ~ w w w w e w w ~ w w e w ~ w w w w w e e e w w w e w w e w e w e w w w e e e e w w w e w w w w e e w e w w ~ w w w e w w e w w w w w w w w w w 93

5.3.1 In utero and early childhood noise exposures . . . .. . . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . 93

5.3.2 Noisy teenage hobbies.. .. . . . . . . . . . . . . . . . . . . . .... . .. . . . . . . . -. . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . 94

5.3.3 Long-term effects of otitis media .................................................. 95

5.4 Hearing Threshold Asymmetry: The 'Ear' Effect wwewwwwwwwwwwowwwwwmwwww~w~9S

5.5 Limitations and Weaknesses of the Study w e e w w w w w e w w w w w w w e w w w e e w w e e m w w w w w e w w w w e w w 97

5.5.1 Shidy design. .. . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . .. . . . . . . . . . . . . . . .. .. . . . . . . . . . . . . . . .. .. . . . .. 97

5.5.2 Study Unplementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS eweeweeoeewwewewwew99

viii

LIST OF TABLES

Table 4 . 1 Statistics on school participation .................................................................... 4 6

Table 4 . 2 Working status of mothers during pregnancy across schools ................ .. ............ 49

Table 4 . 3 Workplace noise exposures across schools ...................................................... 50

........................................................................... Table 4 . 4 Reported workplace noise sources 51

Table 4 . 5 Reported noise at work according to workplace ...................................................... 52

Table 4 . 6 Leisure noise sources ............................................................................................... 53

Table 4 . 7 Time exposed to reported leisure noise sources ...................................................... 53

Table 4 . 8 Student gender distribution arnong schools ............................................................. 54

Table 4 . 9 Student health information .................................................................................... 5 5

Table 4 . 10 Subject health information fiom detailed questionnaire responses ....................... 61

Table 4 . 1 1 Mother's workplace and workplace noise ............................................................. 62

Table 4 . 12 Occupationally exposed mothers ........................................................................... 63

Table 4 . 13 Mothers reporting noise at work

............................. (who were not "considered occupationally exposed to noise") 65

Table 4 . 14 Subjects' noisy hobbies ................................................................................... 66

Table 4 . 15 Reported noisy recreational activities of mothea during pregnancy .................... 67

Table 4 . 16 Dmgs reported by subjects and mothers during pregnancy ................................... 69

Table 4 . 17 Pure-tone hearing thresholds (dB SPL) and corxesponding hearing levels

......................... (dl3 HL) obtained with the TDH-49P headset in N=26 teenagers 71

Table 4 . 18 Threshold differences between ears (Lefi . Right) across Uidividuals at each

of the tested fiequencies ...................................................................................... 7 2

................................................... Table 4 . 19 Repeated measures ANOVA on threshold data 7 4

ix

Table 4 - 20 Statistically significant hearing threshold differences between ears for

specific fiequencies ................................................................................................ 75

Table 4 - 2 1 Consonant discrimination (FAAF test) results for N=26 subjects ......................... 75

Table 4 - 22 Repeated measures ANOVA on FAAF Scores ................................................ 76

Table 4 - 23 Contingency table for otitis media history and FAAF scores in noise .................. 80

Table 4 - 24 Contingency table for rnother's work during pregnancy and subject's

FAAF scores in noise ............... . ........................................................................... 80

Table 4 - 25 Contingency table for noise at rnother's work and subject's FAAF scores

in noise ................................................................................................................... 81

Table 4 - 26 Contingency table for rnother's noisy hobbies duriag pregnancy and

subject's FAAF scores in noise .............................................................................. 81

Table 4 - 27 Contingency table for subjects playing music in a band and FAAF scores

in noise ........................................................................................ , . - ................ 82

Table 4 - 28 Contingency table for subjects listening to music with earphones and

FAAF scores in noise ............................................................................................ 82

Table 4 - 29 Significant mixed design repeated-measures ANOVA results for

hearing thresholds, according to otitis media history ............................................ 84

Table 5 - 1 Cornparison of hearing thresholds in dB HL between this study (2000)

and the Margolis snidy (2000) 1531 averaged across lefi and right ears .................. 86

Table 5 - 2 Comparison of hearing thresholds in dB SPL between femaies fiom the

present study (2000) and the Lopponen study (1991) 1721 femde group

averaged across lefi and nght ears. ....................................................................... 86

Table 5 - 4 Comparison of hearing thresholds in dB HL between this study (2000)

and the Burén study (1992) [78] averaged across left and right ears ...................... 88

Table 5 - 5 Cornparison of hearing thresholds (in dB SPL) between the present study

(N=26) and the Abel study [73] WZO) according to ear. ...................................... 90

.............................................................................. Figure 2 -1 The Human Auditory Apparatus 3 1

................................................................................. . Figure 2 2 Cross-Section of the Cochlea 31

. ...............................................-......-...--.. Figure 2 3 Mammalian Auditory Hair Ce11 Structure 32

. ..................................*.....-.-.....-...---............ Figure 2 4 Supporthg Cells in the Organ of Corti 33

. ....................................................*........ Figure 2 5 Merent Innervation in the Organ of Corti 35

............................................................... Figure 2 . 6 The Auditory Pathways in the Brainstem 36

Figure 4 -1 Location . Type of Institution and Gender-Specificity of the 6 Greater Toronto

Area High Schools ................................................................................................... 47

Figure 4 . 2 Subject Gender and Age Distribution (N=26) ....................................................... 57

Figure 4 . 3 Subject Birth Information (N=26) .......................................................................... 59

Figure 4 . 4 Alcohol intake during pregnancy (N=26) ............................................................... 70

Figure 4 . 5 Mean hearing thresholds as a hc t i on of kquency for right and lefi ears

(in 26 subjects) ...................................................................................................... 73

Figure 4 . 6 Mean Initial and Final Consonant Scores in Quiet and in Speech-Spectrum Noise

(in 26 Subjects) ....................................................................................................... 78

xii

LIST OF APPENDICES

Title . Page

........................................... Letter to Parents and Students 102

................................................. Screening Questionnaire 104

.................................................... Detailed Questionnaire 109

Consent Fonn .............................................................. 119

Data Sheets ................................................................. 121

Threshold Tracking .................................... 122

FAA F da fa ............................................. 123

Sample FAAF Test ........................................................ 124

... Xll l

CHAPTER 1 : INTRODUCTION

It is well established that prolonged exposure to noise can result in

a permanent hearing loss, commonly known as noise-induced hearing loss

(NIHL). No matter where one lives, one is exposed to noise from the

environment, whether it be from £ a m tractors, nearby airports or city

traffic. These noise sources are sometimes referred to as

environmental or community noise [l] and exposure generally cannot be

controlled by the individual. However, there exist many situations

where an individual's choice of activities results in noise exposure

(e-g., loud music, the use of power tools, snowmobiling) . These

sources are sometimes referred to as recreational or leisure noise

sources.

Hearing loss, although not determined by age, tends to be more

prevalent in the older population. The impact of hearing loss

naturally depends upon the degree and the type experienced by an

individual, but the age of onset also plays a major role. Individuals

who lose their hearing in infancy will face problems in language

development [2,3] . The major effect of a hearing loss is the loss of

audibility for some or al1 of the important speech cues. The more

severe the loss, the greater the impairment on language development

and communication [2,3,4]. After the first year, such auditory

impairment results in inattention, mild language delay, and mild

speech problems. This child can only hear the louder voiced speech

sounds. Vowel sounds are heard clearly, but voiceless consonants may

1

2

be missed. In later years, a hearing loss may result in difficulty

communicating at work and with othexs , impaired aesthetic appreciation

(e.g. music, singing), impaired ability to hear alarms (at work and at

home) and psychological embarrassment, which may lead to social

isolation.

1.1 Hearing Acuitv in Teenagers and Young Adults

Recent studies [ S I 61 have show that hearing

otologically normal young adults are not as good as

international standards (e.g., ISO 389, 7029) [7,8] .

lead to the hypothesis that in recent years factors

thresholds in

those given in

These findings

have come into

play which may, even before birth, have a harmful influence on the

human auditory apparatus. Consequently, many of the factors once

believed to only manifest as hearing losses during adulthood may also

be causing changes to hearing in younger groups. Northern et al [31

give some noteworthy statistics on hearing loss in children in the US.

They mention that about one child in 1000 is born profoundly deaf

(also in JZrvelin et al [2]), adding that 2/1000 will acquire deafness

in early childhood, that 1/50 is hearing impaired in the neonatal

intensive care unit (NICU) and that nearly al1 children, from birth

until 11 years of age, are affected by ear infections (otitis media)

with consequent temporary or permanent hearing loss. Northern et al

[31 also mention the alarming finding based on auditory screening in

schools that 10-15% of children cannot hear within normal limits.

Jarvelin et al [ 2 ] report that 14-15% of children have a mild hearing

loss (defined as 15-20 dB HL) at high or low frequencies by the age of

3

14 years. This statement is in accordance with the findings of a study

conducted by Niskar et al [ 4 ] . Consequently, it cornes as no surprise

that concern has been growing over the status of hearing in children

and young adults ,

1.2 Studv Objectives

The objective of this study was to expand the available database on

hearing and speech understanding in adolescents. This was accomplished

by :

identifying a group of teenagers willing to participate in the

study, living in an urban centre;

3 determining their hearing acuity and cornparing to results f r o m

other published studies including normal hearing teenage and

young adult subjects; and speech understanding in quiet and

noisy surroundings;

3 assessing the relationship of these outcomes to noise exposures,

ear status (e-g., otitis media), family history and other

factors of previously demonstrated relevance.

CHAPTER 2: LITERAT= REVIEW

2.1 Noise and Hearing

2.1 .1 The Auditon Amaratus

2.1.1 .l The outer and middle ear

The outer structure of the auditory apparatus is the auricle (also

called the pinna). It collects and conveys sound to the auditory

canal. The auricle develops during the 3rd or 4th week of gestation.

Its final adult shape is reached by the 20th week of gestation (around

the third trimester of pregnancy) but continues to grow until the age

of 9 years (Figure 2 - 1). The importance of the auricle is related to

its ability to aid sound localization, particularly front/back

discrimination of high frequencies. When a sound source is behind the

ear, sound waves will scatter off the edge of the auricle and

interfere with the transmitted wave causing intensity and spectrum

changes in the 3-6 kHz region [91 .

Sound waves travel along the external auditory canal (also referred to

as the auditory meatus) before encountering the tympanic membrane. The

auditory meatus extends approximately 4 cm from the pinna to the

tympanic membrane (Figure 2 - 1). Oscillations of the tympanic

membrane (ear d a m ) are transmitted to three tiny bones comected in

sequence called the ossicles (malleus, incus, and stapes) . Movements from the ossicular chain terminate at the footplate of the stapes,

which transmits the energy to the oval window at the base of the

4

5

peripheral end organ for hearing (the cochlea) , located in the imer

ear (Figure 2 - 1) . At birth, the external auditory canal has no bony

portion and the canal is short and straight, whereas in the adult it

is longer and curves [3]. The tympanic membrane begins its development

at about the 11th week of gestation. As for the ossicles, they begin

their development around the 8th week and reach adult size by the

eighth month. They are fully a ossified B by the 21st week of

gestation 1101.

2.1.1.2 The inner ear

The cochlea, a structure of snail-like appearance (Figure 2 - 2), is

imbedded deep into the temporal bone. It is about 1 cm wide and,

uncoiled, runs 5 mm from the base to the apex and contains a coiled

basilar membrane about 35 mm long. The cochlea begins to develop by

the 28th day of gestation and complete coiling of the cochlea occurs

around the 8th to 9th week of gestation Ill]. Full morphological

development of the cochlea occurs around the 10th week of gestation

(first trimester) and reaches adult size by the 20th week.

A cross-section drawing of the cochlea (Figure 2 - 2) shows that it is

subdivided into three main ' compartments ' , namely the scala vestibuli

(top), scala media (centre), and scala tympani (bottom). Reissner's

membrane separates the scala media from the scala vestibuli. The scala

vestibuli and scala tympani are f illed with perilymph, which is rich

in sodium and low in potassium ions e . , similar to that of the

cerebrospinal fluid and extracellular f luid) . The scala media, on the

6

other hand, is filled with endolymph which is rich in potassium ions

and rather low in sodium ions.

2.1.1.3 Hearinp and the orean of Corti

The peripheral organ of hearing, the organ of Corti, is housed in the

scala media. It is covered by a gelatinous membrane called the

tectorial membrane. Ariother membrane, the basilar membrane (Figure 2 -

2), supports the organ of Corti and gives it rigidity along its

length. Figure 2 - 4 shows how the basilar membrane also supports the

pillar cells, which form the tunnel of Corti, and the supporting cells

of Deiters, which help support the basal end of the outer hair cells.

From the 10'" to the 2oth week of gestation, fœtal cochlear development

is characterized by an opening of the tunnel of Corti and the release

of the tectorial membrane Cl01 . After the 20th week, the main changes

observed under the light microscope include elongation of the outer

pillars, the outer hair cells, and a development cf the supporting

cells of Dieters I l l ] .

Hair cells in the organ of Corti are the peripheral generating source

of action potentials. It is the action potentials produced by the hair

ce119 which send neural information to the cerebral cortex and thus

enable "hearing" , Each hair ce11 is covered by stereocilia which are

connected at the top by tip-links (Figure 2 - 3) which, in turn, are

comected to ion charnels. Between the 11th and the 13th week, hair

ce11 ciliogenesis occurs in a basal-to-apical and inner-to-outer hair

ce11 gradient. An adult-like organization of stereocilia is observed

in the 22 week old fatal cochlea [Il]. The deflection of stereocilia

is provided by movements of the basilar membrane. Vibrations of the

oval window by motion £rom the footplate of the stapes causes a

movement of cochlear fluid, displacing it towards the round window.

This movement of fluid initiates, in return, a wave of displacement on

the basilar membrane which travels apically in the cochlea (i-e., £rom

stapes to apex ) . The direction of movement either relaxes the tip-

links or stretches them and thus opens (or closes) the ion charnels

admitting or preventing ions from flowing in and out of the hair

cells.

The basilar membrane exhibits frequency selectivity, for if one

introduces a sound (described by a sine wave) of specific frequency,

one can observe a sharp peak confined to a specific region on the

basilar membrane. This phenomenon was first observed by Von Békésy

[12] and is referred to as place coding - the ability of the ear to

discriminate between different frequencies. The traveling wave along

the basilar membrane shows different peaks according to frequency. The

higher frequencies peak near the base of the cochlea and die off

rather quickly while the lower frequencies peak near the apex and die

off more slowly. Therefore, it can be said that the basilar membrane

acts in some way as a low-pass filter.

There are three rows of outer hair cells and only one row of inner

hair cells along the length of the organ of Corti, as can be seen in

Figure 2 - 2. The outer and inner hair cells also differ in shape and

function. The inner hair ce11 is shaped like a flask, while the outer

hair ce11 is cylindrical (Figure 2 - 3). The longest of the outer hair

ce11 stereocilia are embedded into the tectorial membrane- It is not

believed that any of the imer hair cells are embedded in the

tectorial membrane. In fact, studies involving chernical removal of the

outer hair cells provide some evidence suggesting that it is the outer

hair cells which contribute to the production of the low-threshold,

sharply-tuned, component of the mechanical wave traveling along the

basilar membrane (Figure 2 - 2) (121 , Other functional dif f erences

between outer and inner hair cells involve patterns of neuronal

innervation in the organ of Corti.

The cochlear nerve is the peripheral, afferent, pathway relaying

auditory information to the central nervous system. In humans,

approximately 30,000 axons make up the cochlear nerve [12,13l . Ce11 bodies of the afferent neurones are found in the spiral ganglia of the

cochlea (Figure 2 - 5). The cells of the afferent pathway are bipolar

and relay information back and forth between hair cells and the

cochlear nucleus in the brainstem (Figure 2 - 6 . A great majority

(90-95%) of the afferent fibers terminate on the inner hair cells with

up to 20 fibers connecting to each inner hair ce11 and are referred to

as Type 1 fibers. Cochlear nerve fiber recordings provide evidence

that afferents do not synapse with other neurones or with each other,

but rather communicate the activity of individual inner hair cells.

Once the inner hair ce11 dies, the spiral ganglion which innervated

the ce11 will degenerate. The remaining 5-10% are called Type II

fibers and can each innervate nurnerous outer hair cells [12,141. As

opposed to the thick myelinated axons of the Type 1 fibers, axons from

type II fibers are fine and unmyelinated. Efferent fibers originate in

9

the superior olivary complex in the brainstem (Figure 2 - 6 ) and

contact the imer hair cells directly. However, efferent fibers

destined for outer hair cells are myelinated and connect to the base

of the outer hair ce11 (Figure 2 - 3) [151 .

The myelinization process of the auditory pathways begins around the

20th week of gestation and is not yet completed at birth. Nonetheless,

these pathways are still fully functional [ 3 ] . Inner hair cells mature

earlier than outer hair cells. In the beginning, outer hair cells are

exclusively innervated by afferent fibres. Mature efferent outer hair

ce11 synapses are not fourid until 1 or 2 months after the 20th week of

gestation (i.e. by the 3rd trimester of pregnancy) [Il].

2.1.1.4 The cochlea's enerw s u ~ p l i v

The energy required to sustain the 'cochlear transducerl is provided

by the stria vascularis (Figure 2 - 2). Although glucose, fatty-acids,

and amino acids are al1 potential sources of energy, glucose is the

major energy substrate of the inner ear. It is supplied by the

vascular system and crosses the blood-perilymph barrier through

facilitated transport Cl61 .

2.1.2 Tem~orary and Permanent Threshold Shifis

Almost immediately after exposure to noise, the peripheral organ of

hearing e , the cochlea) exhibits morphological changes which

affect hearing thresholds. However, some of these changes are

temporary and normal auditory function returns. Such temporary changes

10

are ref erred to as temporary threshold shif t (TTS) . Typically, with

prolonged noise exposures such as occupational exposures, auditory

function does not return. This irreversible damage is known as

permanent threshold shift (PTS) . The relationship between TTS and PTS

is complex and difficult to interpret. The precise mechanisms

underlying TTS and PTS are not well understood and are the subject of

numerous studies. Many types of noise exposures can cause TTS (e .g-,

exposure to high-level sound £rom rock concerts) and PTS (e .g., years

of continuous (8 hrs) daily exposure to compressor machine noise at

work). Leisure noise sources, such as loud music, receive the most

attention in studies concerning exposures in adolescents and young

adults. Such sources, especially rock concerts and discotheques, are

well recognized as producing TTS [5,6,17].

2.1.2.1 Underlving Mechanisms of Tem~orarv and Permanent Threshold Shift

Resufts from various studies have given rise to several hypotheses

concerning the specific mechanisms involved in damage from noise

exposures. These include ischemic damage to cells in the stria

vascularis (Figure 2 - 2) and metabolic exhaustion, while

electrophysiological studies reported excitotoxic damage [18,19]. In

addition, pathological findings on hair cell stereocillia have

revealed mechanical damage, such as severed tip links (Figure 2 - 3 )

ml .

The wide diversity of results surrounding the possible mechanisms

involved in TTS and PTS arise mostly from inter-animal variability.

This is because al1 individuals being exposed to the same damaging

noise will not sustain the same amount of damage 1211 . In order to

differentiate between damage that causes TTS and damage that causes

PTS, one needs to eliminate differences arising from inter-animal (or

inter-unit) susceptibility to noise. Results of a study conducted by

Bohne and coworkers [21] showed that an animal exposed to noise

binaurally will develop approximately the same amount of damage in

each ear. Similar studies revealing inter-animal variability have been

mentioned by Bohne et al [22]. They subsequently developed a new

technique called 'survival-fixation" to minimize problems due ta

variations in susceptibility to noise damage that occurs when

comparing damaged cochleae from different animals (e-g., comparing the

left ear of guinea pig A with the left ear of guinea pig BI.

Survival-fixation consists of chemically fixing one of the animal's

cochleae immediately after binaural noise exposure and fixing the

other cochlea at a much later post-exposure time. The survival-fixed

cochlea of control (non noise-exposed) animals showed no difference in

magnitude or pattern of hair ce11 loss when compared with the

terminally-fixed cochlea. In their study, Bohne et al [223 showed that

survival fixation did not alter the degeneration and healing processes

in the opposite, terminally-fixed, cochlea. Finally, this technique

enabled the fixed specimen to be retained for histopathological study

at a later date.

The technique described above was employed by Nordmann and coworkers

1191 in their West to elucidate pathological differences between

damage consisting of TTS and that causing PTS. In their experiment,

chinchillas were continually

with a centre frequency of 4

exposed for 24 hours to octave band noise

kHz at 86 dB SPL to produce moderate TTS.

Al1 11 chinchillas exposed to the noise developed a TTS of similar

magnitude in the survival-fixed cochlea. However, only 4 out of 8

terminally-fixed cochleae (i.e., those that were allowed to recover or

stabilize their hearing thresholds) developed a PTS at 6, 7 , 13, and

27 days post-exposure, respectively. This finding suggests that

susceptibility to noise depends upon recovery or repair processes

within the cochlea rather than the magnitude of the initial threshold

shift .

The histopathological findings for TTS damage included outer hair ce11

stereocilia which were no longer embedded in the tectorial membrane in

the region of the TTS. In those who developed a PTS, there were focal

losses of inner and outer hair cells and afferent nerve fibers at the

corresponding frequency location of the PTS . Hence , the investigators

concluded that although TTS and PTS may occur in the same individual,

their underlying mechanisms are different and that TTS does not

necessarily result in the later development of PTS f191.

A review by Quaranta et al [231 described studies where subsequent

exposure to noise did not produce as much TTS as the initial exposure

in both animals and humans. The results were attributed to the

acoustic reflex (AR), also known as the middle ear or stapedial

reflex. Under efferent control, muscles in the middle ear contract

following intense acoustic stimuli. T h e two muscles involved are the

tensor tympani, which is attached to the malleus near the tympanic

13

membrane and innervated by the trigeminal (Sth) cranial nerve, and the

stapedius muscle which is attached to the stapes and imenrated by the

facial (7th) cranial nerve (Figure 2 - 1) 191 . Although both muscles are believed to take part in the acoustic reflex, some studies in

mammals (including humans) have indicated that the tensor tympani was

unaffected by acoustic stimuli and the sound attenuation was due

almost exclusively to the contraction of the stapedial muscle [23,241.

The AR mechanism is believed to play a protective role against noise

damage through a frequency-dependent attenuation of the sounds

reaching the inner ear [9,23,24,25] . However, the extent of its

defensive role is limited by several factors. Firstly, the latency in

onset (50-100 msec 1231) of this mechanism is believed to be too long

for protection against impulse noises, which can be orders of

magnitude shorter i e microseconds) . Secondly, it is fimited to

lowex frequency sounds (below 2 kHz in humans [23] ) and weakens when

exposed to the stimuli for long periods [25] . Predictably, drugs

affecting neurotransmission, such as sedative-hypnotics, can also

reduce the amount of protection offered by the acoustic reflex 1251 .

With pure tones, the acoustic reflex is normally observed at levels of

85 to 100 dB SPL in humans [24].

The most important role of the acoustic reflex is reducing the amount

of TTS following certain noise exposures [23,26]. However, it has been

shown that PTS severity can also be reduced by the acoustic reflex

126,271 . In their study on humans with Bell's Palsy (including

stapedial muscle palsy), Borg and coworkers ES71 found that ears

without the acoustic reflex had a PTS 30-40 dB larger than ears with

normal stapedial function. As well, the authors observed that ears

without AR would display more loss at higher fxequencies than those

with normal acoustic reflex. This finding has led to the belief that

perhaps AR parameters may predict an individual's susceptibility to

PTS .

Another way of preventing the severity of PTS was described by

McFadden et al [28]. Their experiment with chinchillas showed

increased resistance to acoustic trauma, caused by 48 hrs of exposure

to 106 dB SPL octave band noise centred at 0.5 kHz, with low-frequency

'conditioning' (conditioned 6hrs/day for 10 days by 90 or 95 dB SPL

octave band noise centred at O. 5 kHz) . Although the conditioned

animals developed less PTS than controls, they sustained as much hair

ce11 loss following the high-level noise exposure. These results

suggest that low-frequency conditioning does not necessarily protect

Erom hair ce11 loss in the chinchilla but may protect the cochlea £rom

other forms of damage (e .g., changes in homeostasis) . Anothez:

interesting finding was that conditioning could provide protection for

a longer period than had previously been demonstrated. Most studies

observed protective effects 30 days post-exposure, while this study

obtained similar results after 60 days. Such conditioning-induced

resistance, also known as training or toughening effects, have

previously been described in chinchillas, guinea pigs, rabbits and

humans 126,281 .

For many years, it was theorized that TTS could be used to pxedict

individual susceptibility to PTS. This has been questioned in more

recent studies [23,l9] . In summary, TTS remains the f irst noticeable

effect directly following intense noise exposure, while PTS takes

longer to manifest. Permanent threshold s h i f t tends to occur following

daily noise exposures over several years. Repeated assaults to the

auditory apparatus are known to induce pathological changes of inner

ear mechanical and sensorial structures. However, these ce11 lesions

may or may not directly correlate with the clinically obsenred PTS.

More recent studies, such as the one by Nordmann et al 1191 , suggest

that the physiological damage causing TTS may be distinct £rom that

causing PTS .

Fundamental knowledge about the processes of deteriorat ion and

regeneration, as well as the protective effects of AR and low-

frequency conditioning in the noise-exposed cochlea are highly

important. Their understanding may rcveal ways in which to protect

humans and prevent hearing loss. If damage causing temporary hearing

loss is t ~ l y distinct from that causing permanent hearing loss, the

types of noise exposures causing permanent damage could be more

clearly identified. The acoustic reflex is a well known protective

mechanism in humans but has only been reported in adults. If this

protective mechanism does not occur in the fœtus, it might increase

the risk for hearing loss in children born of mothers exposed, during

their pregnancy, to loud work-related or recreational noise. The

identification of a fœtal acoustic reflex would be helpful in risk

16

assessment, especially for fœtal industrial noise exposures, given

that many of the sources found in industry have high levels of low-

frequency noise which penetrate the womb (see section 2.2.1).

Types of hearinp loss (Conductive vs Sensorineural)

In humans, sound can be transmitted to the inner ear either by air or

bone [9] . The air conduction pathway (described in the previous

sections) involves the external auditory meatus, the tympanic membrane

and the ossicular chain. The bone conduction pathway, however,

involves the transmission of sound vibration to the skull bone,

including the temporal bone, which houses the cochlea, When reaching

the bony stiell of the cochlea, the vibrations stimulate the inner ear.

Using a bone vibrator, Sohmer et al [29] have shown that skull

vibrations also create pressure fluctuations in the cerebrospinal

fluid (CSF) which then spreads to the fluids of the inner ear.

In conductive hearing loss there is an interference in the

transmission of sound waves from the external auditory meatus to the

inner ear. The inner ear itself functions properly, however, there is

a defect in the air conduction pathway preventing the sound £rom

reaching the i ~ e r ear. Since bone conduction is not affected, some

sound can be heard via this pathway. In children, conductive losses

are usually caused by otitis media (middle ear infection) and usually

resolve spontaneously [3] . However, permanent changes in bone

conduction thresholds have been observed following surgery for chronic

otitis media [301 .

Sensorineural hearing loss involves hearing loss due to either damage

suffered by the organ of Corti or from damage caused to any of the

nerves involved in the auditory pathway (Figures 2 - 2 & 2 - 6). These

types of damage are not readily differentiable by most testing

methods. Progressive sensorineural hearing loss may be related to bony

disease causing intrusions into the audi tory nerve or membranous

labyrinth, metabolic disease, serious bacterial and viral infections,

as well as familial inheritance [ 3 ] . Sensorineural hearing loss is

nearly always irreversible.

2.2 Noise-Induced Hearing Loss: From The Womb To Earlv Adultbood

2.2.1 Fœtal Noise Exposures -

In a healthy subject with normal hearing, various responses will occur

as a result of sound stimulation. Several methods have been developed

to identify whether the fœtus can actually hear the sound that

reaches the uterus. These include the blink-startle response 1311,

auditory brainstem evoked potentials (ABEP) and auditory brainstem

response (ABRI. The latter has been developed to test the integrity of

the central auditory pathway (Figure 2 - 6) . ABE2 are classif ied by:

(a) the relative latency of components (short, middle, or long) , (b)

the presumed anatomical site of generation (cochlea, brainstem.

cerebrum) , and (c) the relative dependence on stimulus or subject

factors L e . , exogenous or endogenous, respectively) .

ABR is used clinically because it provides an objective method of

quantifying the functions of both peripheral (middle ear and cochlea)

and central auditory pathway in the brainstem [32] . Short-latency auditory evoked potentials represent the brainstem exogenous

potentials. These are a series of 7 vertex-positive components

(labelled waves 1 to VII) , identified during the first 8 msec [33,34l

in animals, or 9 msec [35,36,37] in humans, following the presentation

of a click stimulus. A study in cats [38] revealed that wave 1

originates in the 8'" cranial nerve within the cochlea and cochlear

nucleus (Figure 2 - 6) . Wave II originates f rom the ipsilateral

cochlear nucleus and superior olivairy complex, while wave II 1

originates in the brainstem and is attributed to the contralateral

superior olivary complex [38]. Wave IV originates in the contralateral

olivary complex and lateral lemniscus nucleus (Figure 2 - 6) , while

wave V originates in both inferior colliculi [38]. Similarities in

structure and function of brainstem auditory centres between cats and

humans were identif ied by Moore [39] . It is important to note that, in clinical studies on humans, waves IV and V may be fused and that other

components such as waves II, VI and VI1 may be absent in normal

hearing subjects [401 .

A study by Cook and coworkers [41] recorded ABR in guinea pig pups

exposed, in utero, to noise at 115 dB SPL for 7.5 hours/day (varying

days). They found increases in peak wave IV latencies. In their

interpretations, they assumed that peak wave IV in the guinea pig

corresponded roughly to wave V in the human. Two ABR studies,

conducted on foetal sheep exposed to 120 dB SPL (either in free-field

19

[42] or via a bone oscillator secured to the fœtal skull [431)

continuously for 16 hours, f ound increases in ABR thresholds (approx.

8 dB) for low frequency (cl IcHz) tone bursts and increases in wave IV

latencies. These studies [41,42,43] demonstrate clearly that low-

frequency sounds can penetrate the womb and are readily detected by

the fœtal auditory apparatus in these animals.

Since the outer and middle fœtal ear are f illed with amniotic fluid,

it remains questionable whether the fœtus can "hear" by way of the air

conduction pathway. Because the uterine environment is also filled

with fluid, the transfer function of the fœtal inner ear cannot be

easily determined. Gerhardt and coworkers [44] recorded the cochlear

microphonic (CM) , in fœtal sheep after presenting tone bursts at 0.5,

1, and 2 kHz. In cells of the inner ear, there are resting and

stimulus-related electric potentials. The outer hair ce11 restinq

potential is -70 mV and that of the inner hair ce11 is -45 mV [121 . When the ear is stimulated, two additional potentials occur, separate

£rom nerve action potentials. They are the cochlear microphonic and

the summating potential. The former is an AC potential that mimics the

amplitude of motion of the outer hair cells. Its characteristics

include occurrence with essentially no latency (other than travel time

d o m the auditory canal) and growth, in proportion to the size of the

stimulus, and identical phase and frequency to the stimulus [12] . The cochlear microphonic can be recorded from the round window (Figure 2 -

1) .

20

Recording of sheep CM in utero, by Gerhardt et al [44] , was done under

3 different conditions: 1) head uncovered ; 2) head covered with a

neoprene hood ; and 3 ) head covered with neoprene hood bearing a hole

that permitted the auricle and ear canal to be exposed. The CM

recorded under the first condition showed more sensitivity than that

under condit ion 2, while there were no not iceable dif f erences between

conditions 2 and 3. If the middle ear pathway was the major pathway

used by the fœtus for hearing, condition 2 should have resulted in

greater sound attenuation to the external auditory meatus than

condition 3. They concluded, therefore, that the fœtus hears rnainly

through bone conduction. Hence, there exists a potential for adverse

effects inflicted by high intensity noises on the fœtal cochlea. A

similar experiment was conducted by Hollien and Feinstein [451 with

human divers. They concluded that underwater sound energy is

transduced predominantly by bone conduction rather than by air

conduction in the adult human. This is a significant finding since the

fœtus can be exposed to maternal occupational noise sources, as well

as maternal recreational noise sources. These Vary in exposure time

and intensity and may include sources such as amplified music, power

tools, firearms and recreational vehicles such as snowmobiles and

motorcycles [ 4 6 ] .

2.2.2 Noise Exposures fiom Toys During Childhood

Some types of toys for children can produce sounds capable of causing

hearing loss 1461. Hellstrom and cowoxkers [ 4 7 ] measured noise levels

associated with toys and recreational articles used by children in

21

Finland. The types of toys tested included baby toys, such as squeeze

toys and rattles as well as impulse generating toys, including cap

guns and firecrackers. Al1 measurements were made in 1/3 octave bands

£rom 20 to 20,000 Hz and rnimicked real-life exposure times (e.g., a

child may shake a xattle repeatedly but only a few seconds each time

and wonf t usually do so al1 day long). Peak sound pressure levels for

impulse generating toys were measured in C-weighted (dBC) sound

pressure levels, while maximum levels for other toys were expressed in

A-weighted sound pressure levels (&A) . The A-weighting curve was

originally designed to weight sound pressure levels as a function of

the frequency response characteristics of the adult human auditory

system for pure tones of low intensity level. The mid-frequency region

is emphasized while high and, particularly, low frequency regions are

less accentuated. The C-weighted curve also matches the adult human

auditory system's response to pure tones but at much higher intensity

levels. In this case, the low frequency region is given more

importance than in the A-weighted curve [ 4 8 ] . Results £ r o m four

different squeeze toys showed maximum dBA levels of 92.2, 84.0, 100.1,

and 97.8 at frequencies of 0 -8, 10, 10, and 8 kHz respectively. The

results from four rattles, however, showed lower noise levels than the

squeeze toys. The rattle with the highest sound intensity produced a

level of 91.0 &A at 10 kHz, while the lowest level obtained was 74.4

dBA at 10 kHz. All impulse generating toys had measured peak levels of

140 dBC or higher. Compared to squeeze toys and rattles, measured peak

intensities for the impulse generating toys used by older children

were lower in frequency (al1 below 4 kHz, with the exception of two

firecrackers whose maximum output frequencies were 5 and 7 kHz).

Results from this study suggest that many toys and recreational

activities are very noisy and, indeed, may damage hearing in young

children. However, little is known about the susceptibility of the

auditory apparatus to such noise sources in the child (compared to

that in the adult).

2.2.3 Noisy Hobbies and Hearing Loss in Young Adults

Many researchers have attributed the decline in hearing acuity in

young adults ( 18 -20 years) to various recreational activit ies such as

the use of personal cassette (or CD) players (PCPs), attendance at

rock concerts, discotheques, and exposure to other sources of

arnplified music [4,5,6,17,49,50]. Many statistics do, indeed,

demonstrate a high percentage of teenagers participating in such

activities on a regular basis [49]. Most researchers also stress the

importance of exposure time (as well as sound levels) to loud music

from PCPs in assessing the possible risk of hearing loss. A study by

Merluzzi and coworkers [SI, conducted on 18-20 year old males,

reported that 98% of al1 subjects acknowledged listening to music. Of

these, 86% mentioned listening to the 1 - 1 66% used a 'walkman'

(PCP) , and 26% reported attending rock concerts. Up to 85% of music

listeners reported listening to music for more than 1 hour per day. A

total of 64% of al1 subjects said they attended discotheques. Of

these, 30% admitted attending at least once a month and 54% reported

attending 2 to 4 times a month. With regards to the amount of time

spent at the 'disco', 14% of those attending discotheques stated that

they remained for periods of more than 4 hours and 46% reported

23

staying for an average of 2-3 hours. As well, 90% of the discotheque

attendees admitted to having been consistent in their attendance for

as long as one to four years. On average, their audiometric thresholds

were 5 to 10 dB above the 5ofh percentile values reported in database

A, ISO 1999 [51] (fwom a screened population) , depending on frequency.

They corresponded more closely to the goth percentile values and appear

to suggest a decline in hearing in recent years which might be

attributable to leisure noise exposure.

An experiment conducted by Hellstr6m et al 1171 on 21 subjects 13 to

30 years of age (with an average age of 15.3 years) fourid that mean

levels selected by subjects on persona1 listening devices was 93.5

dBA. However, a study by Smith et al 161 reported a much lower average

listening level ( 7 4 dBA) . In this study, noise levels £rom several

nightclubs in different areas of London, England were also measured.

The average sound pressure levels ranged from 85 to 105 dBA, depending

on measurement locations [ 6 ] . Averages weil above 90 dBA were

registered on the dance floor and near the speakers. The lowest noise

levels were recorded in the bar area, with averages anywhere from 75

to 95 dBA, depending on the particular nightclub. Interestingly, noise

levels appeared lowest earlier in the evening (10 pm), reaching a peak

at around midnight with a subsequent slow decrease. Therefore, the

time at which one attends the nightclub is also an important factor in

resultant noise exposure.

2.3 Otitis Media

Reports in the literature describe the additive effects of ear

infections and noise exposures on hearing loss in young adults 1501 .

These additive effects were studied in a population of young adults

reporting exposure to various sources of loud music. Using tonal

automated audiometry, Job et al [SOI measured hearing thresholds in

young males aged 18-24 years. They found that in young men with a

history of otitis media, those using persona1 stereos had thresholds

11 dB HL (SD 2.99) greater than those who did not use persona1

stereos. The effect of persona1 stereo use on hearing thresholds was

statistically significant (p < 0.001) in young men with a history of

otitis media. Conversely, in young men with no history of otitis

media, persona1 stereo use showed no apparent effect on hearing

thresholds [SOI .

Chronic recurrent ear infections may, by themselves, cause hearing

losses. It has been found to be the most commonly associated medical

problem with paediatric sensorineural hearing loss [52]. Statistics

reported by Northern and Doms [3] demonstrate that by the age of 6

years, 90% of children in the United States will have suffered at

least one ear infection. A further 20% with chronic otitis media will

required surgery in order to correct the problem.

A recent study by Margolis and coworkers [53] confirmed previous

reports that children who suffered from chronic otitis media

demonstrated significantly poorer hearing in the extended high

25

frequency range (9-16 kHz) compared to other children. The study

included children aged 9 to 16 years, who had suffered from chronic

otitis media (COM), with a history of myringotomy, aspiration of

middle ear effusion, and insertion of tubes, and a control group, who

did not suffer from COM but had experienced non-chronic otitis media

at least once. The experimental group was further divided in 2 sub-

groups, better hearing (BH) and worse hearing (WH) , according to their

average hearing thresholds in the 0.25-8 kHz range. The lowest hearing

thresholds were obtained for al1 groups at 2 kHz and ranged £rom -1.7

dB HL (control) to 0.2 dB HL (BH) and 3.1 dB HL (WH) . The highest

hearing thresholds were obtained at 8 kHz and ranged £rom 4 . 6 da HL

(control) to 6.9 dB HL (BH) and 11.4 dB HL (WH). Only the WH group

showed any significant high-frequency hearing loss when compared to

both the control group and the BH group (p ~0.001).

2.4 Other Sources of Hearing Loss

2.4.1 Conseciuences of illness

Various diseases such as meningitis, mumps, measles, and jaundice have

also been associated with hearing loss. In most bacterial infections,

damage to the i ~ e r ear results £rom in£ iltration of the organism via

the interna1 meatus (Figure 2 - 1). Viral diseases may cause

histopathological damage to the orgm of Corti, damage or complete

destruction of the stria vascularis and tectorial membrane, and

atrophy or destruction of the neural pathways [ 3 ] . These diseases can

affect children of al1 ages, including fœtuses, newbom and pre-term

infants. Studies on premature babies [54,551, especially those Who

spent time in a neonatal intensive care unit (NiCu) [3,521 , showed an

increased risk of sensorineural hearing loss in these infants compared

to full-term infants. One of the reasons may be that pre-term infants

tend to require more medications and suffer more frequently from

medical conditions such as jaundice, metabolic acidosis, and have

weaker immune systems . As well, noise f rom machines in the NICU may be

contributing to the observed hearing loss.

Materna1 diseases during pregnancy may also pose a risk of auditory

damage to the unborn child. Congenital infections such as syphilis are

known to cause several central nervous system abnormalities but often

result in foetal death and miscarriage E3 1 . A recent study f ound

hearing defects in children born of mothers who had suffered from

symptomatic rubella during their pregnancy [56] . This study measured

transmission rates of 87.5% in symptomatic rubella from rnother to

fœtus during the first three months of pregnancy.

Several medications have also received much attention in terms of

potential harmful effects on hearing. Drugs such as salicylates,

aminoglycoside antibiotics and loop diuretics have long been known to

adversely affect hearing 1571 . A recent study of the effects of

salicylates on outer hair cells by Lue and Brownell [58] supported the

theories that salicylates, at therapeutic levels, diminish

electromotile responses in outer hair cells and also produce hearing

27

loss and tinnitus in human subjects. These effects, however, are

reversible upon discontinuation of salicylate therapy.

Dxugs can also have a positive effect, or protective effect, on

heâring. In Canada, there are approximately 2 million people, aged 12

years and older, who suffer from asthma 1593 . Medications used for prophylaxis of this disease include anti-inflamatory steroids such as

prednisolone and inhaled bronchodilators such as the glocucoxticoids.

It has been shown [18] that inflammatory tissue alterations (elicited

by cellular damage, tissue hypoxia and ischemia) occur in various

structures of the cochlea following noise exposure . In addition, Lamm

et al [60] cite various studies that identified glucocorticoid

receptors in many cochlear and vestibular tissues. They then studied

the possible protective effects of diclofenac (a non-steroidal anti-

inf lammatory agent) , Hl blockers (antihistamines) , prednisolone and

glucocorticoids on noise-exposed guinea pig cochleae. Their study

revealed that progressive sensorineural hearing loss (SNHL) could be

successfully treated with glucocorticoids through direct cellular

effects in the cochlea (not taking into account blood flow and

oxygenation) . In non-exposed animals, prednisolone and diclofenac

induced a significant decline in partial oxygen pressure in the

perilymph but did not cause any changes in the cochlear microphonic,

compound action potentials in the auditory nerve or in auditory

brainstern responses. The Hl blockers did not produce any effects in

the noise-exposed animals.

2.4.3 Phvsical barriers

Hearing loss rnay also be associated with a build-up of ear wax in the

external auditory meatus. Ear wax is produced by the apocrine and

sebaceous glands of the ear canal and is normally removed from the

canal by migratory movements of the epithelium. However, some people

may produce excessive ear wax or have an inadequate cleaning

mechanism. Such accumulation of wax blocks the ear canal and can,

subsequently, cause hearing loss [3 ] .

2.4.4 Age

Ageing rernains the most important risk factor for hearing loss. A

gradua1 increase of hearing thresholds with age has been well

demonstrated and is known as presbyacusis. Although the existence of

the relationship between hearing loss and agei~g has been demonstrated

convincingly and conclusively, very little is understood about the

precise nature of the effect of the ageing process on hearing. It is

also important to note that in older subjects, it often proves

difficult to distinguish between PTS-related hearing loss (see section

2.1.2) and age-related hearing loss since their differences are not

yet well understood [l8,23] .

2.4.5 Gender

There are gender differences in hearing, with respect to both

presbyacusis and noise exposure. Numerous studies have showri

29

di ff erences in hearing thresholds of adult males and females with

thresholds in males increasing more rapidly with age 1511. Studies

including data on xecreat ional noise exposures in teenagers have

revealed that males tend to experience significantly higher levels of

noise exposure than females [6] . Nevertheless, there is some

controversy over whether males and females demonstrate different

ïevels of TTS in different frequency regions [17,61]. These results

seem to indicate that leisure noise exposures, such as loud music, may

be affecting hearing thresholds differently for males and females.

Because music varies greatly in frequency and type of sound (i.e. more

or less high frequency components, more or less pure tones), makes any

gender-specific effect more difficult to interpret.

2.4.6 Low birth weight

Low birth weight has also been associated with hearing loss in

children 131. Other factors influencing birth weight may also directly

contribute to hearing loss, including drinking and smoking by the

mother during pregnancy. A recent study of infants of smoking mothers

showed an increase in arousal thresholds (i.e. the level of sound

necessary to awake the infant) of those children with smoking mothers

compared to those of non-smoking mothers [62].

2.4.7 Genetics

There is also a genetic component to hearing loss. Genes have been

linked with susceptibility to noise-induced hearing loss and as

30

completion of the human genome project approaches. more and more of

these genes are being identif ied C631 .

2.5 Sumrnarv

The information available to date regarding the state of hearing in

young adults and teenagers is highly suggestive of a steady decline in

hearing acuity. However. the precise aetiology of the observed

increase in hearing thresholds remains difficult to ascertain. The

presence of numerous factors acting in concert are making

questionnaires an indispensable tool for studying hearing acuity in a

normal hearing population. In tems of noise exposure, t remains

apparent that by the age of 18 years most people have been exposed to

many hours of noise. whether it be £rom their own volition as children

and teenagers, or through their mothers while still in the womb.

Studies conducted in animal models off er evidence of deleterious

effects of noise on the fœtus. Although caution must be applied in

interpretation of these animal findings, they are indicative of

possible hearing damage to the human fœtus, cauçed by the mother's

exposure to high level recreational or work-related noise, exceeding

safe limits (>85 dBA). Further studies are needed to elucidate the

possible effects of noise, including fœtal noise exposures, on hearing

in young adults.

FIGURE 2 -1 THE HUlMAN AUDITORY APPARATUS

Stapes lncus

I' / Acoustio

membrane \ \

Modified f rom Willems (631 Figure 1 : Drawing of o u t e r , inner, and

middle ear.

FIGURE 2 - 2 CROSS-SECTION OF THE COCHLEA

From Willems [63] Figure 2 : T h e Cochlea.

FIGURE 2 - 3 MAMMALIAN AUDITORY HAIR CELL STRUCTURE

INNER HAlR CELL

Modified From P i c k l e s [12] F i g u r e 3.5

and Willems 1631 F i a u r e 3 : O u t e r hair

OUTER HAIR CELL

34

FIGURE 2 - 4 SUPPORTING CELLS IN THE ORGAN OF CORTI

From Gray's Anatomy [64] FIG. 932 - Schematic of the reticular lamina

and subjacent structures. Key: A - internal rod of Corti, with a , its

plate; B - external rod; C - tunnel of Corti; D - basilar membrane. E

- inner hair cells; 1, 1' - internal and external borders of the

reticular lamina; 2, 2' , 2" - the three rows of circular holes; 3 -

first row of phalanges; 4, 4', 4" - second, third , and fourth rows of

phalanges; 6, 6', 6" - the three rows of outer haix cells; 7 , 7', 7" -

cells of Deiters; 8 - cells of Hensen and Claudius. (Testut)

FIGURE 2 - 5 AFFERENT INNERVATION IN THE ORGAN OF CORTI

From Pickles 1121 Figure 3.6, p . 3 5 . K e y : OHC - outer hair ceil;

IHC - inner hair cell; SG - sipral ganglia.

FIGURE 2 - 6 THE AUDITORY PATEWAYS IN THE BRAINSTEM

AFFERENT EFFERENT

Lateral Lemniseus

Cochlcar Nucleus

Midbrain

Modified from Harrison [65] Figures 1 and 10. Schematic

representations of the auditory pathways in the mammal. Key: DCN -

dorsal cochlear nucleus; AVCN - antero-ventral cochlear nucleus; PVCN

- postero-ventral cochlear nucleus; MTB - medial nucleus of the

trapezoid body; MSO - media1 nucleus of the superior olive; LSO -

lateral nucleus of the superior olive; DLPO - dorso-lateral

periolivary nucleus; DMPO - dorso-medial periolovary nucleus; COCB -

crossed olivocochlear bundle; UOCB - uncrossed olivocochlear bundle.

3.1 Studv Desien

To assemble a group of adolescents 14-16 years of age, the Toronto

District and Catholic School Boards were asked to review the study

protocol and subsequently agreed to provide access to local schools.

Six schools were contacted and a letter, addressed to the principal,

briefly explained the purpose of the study and al1 the procedures

involved (Appendix 1) . Subsequently, teachers identified as liaison

personnel (by the principals at each school) were approached about the

study. They were given screening questionnaires (Appendix II) to

distribute to al1 grades 9 and 10 students. This ensured that subjects

would be within the desired age range (14-16 years) for this study.

Those students interested in participating in the study were asked to

return the completed screening questionnaire to their teachers.

Because the study was concerned with hearing status in normal hearing

adolescents, the exclusion criteria included a history of ear

infections with subsequent surgery, head trauma and a family history

of genetic hearing disorders. These conditions are al1 known to be

associated with hearing 109s. Mothers and students meeting the

selection criteria were later contacted by telephone and told that a

detailed questionnaire (Appendix II 1 ) and consent fonn (Appendix IV)

would be mailed to them, provided parents agreed to allow the

prospect ive candidates to have their hearing tested.

One week following the initial contact, a second telephone cal1 was

made to set up an appointment for the hearing tests. Approxirnately two

days before the scheduled test day, subjects were called to check on

their state of health. Those subjects with colds, infections, or

taking medications which could alter test results were re-scheduled.

Upon arriva1 at the testing facility, each subject returned the

detailed questiomaire that had been completed by his/her mother, as

well as the consent form signed by both the parent and participant.

Hearing threshold measurements were then made on each ear for 9 pure-

tone frequencies, from 0.25 to 10 kHz. A consonant discrimination test

- the Four Alternative Auditory Feature ( F m ) test [66] - was then

performed in quiet at a comfortable sound level of 75 dB SPL. This

test was repeated in a background of speech-spectrum noise, with a

signal-to-noise ratio of -5 dB SPL. The level of the speech was

maintained at 75 dB SPL. The level of the noise was at 80 dB SPL. The

consonant discrimination test was conducted to allow an assessment of

the effect of hearing on speech understanding [67]. The datasheets

used for the two tests, as well as one of the five alternative

versions of the FAAF test are included in Appendixes V I and VI

respectively.

3.2 Survevs

The screening questionnaire was designed to identify those individuals

with conditions which might prevent them £rom having 'normal' hearing.

As well, it served as a reliability check for repeat questions in the

39

detailed questionnaire. The purpose of the detailed questionnaire was

to provide further in-depth information.

Much of the information collected by the detailed questionnaire

concerned the student's lifetime history of exposure to noise.

Detailed information regarding the motherfs occupation during

pregnancy was collected, including job title (with a brief description

of her job), sources of occupational noise exposure, and amount of

time exposed to these sources. Information was also collected on the

motherf s non-occupational noise exposures i . e. , leisure activities) ,

the subjectfs own leisure activities, and medications taken by the

mother (during pregnancy) and sub j ect (lifetime) .

To assess the possible effects of genetic hearing impairments, a

family medical history regarding hearing difficulties was assessed.

Any hearing problems experienced by any of the subject's first order

relatives (i-e. grandparents, parents and siblings) was noted and

checked against k n o w n inherited hearing disorders. Smoking and alcohol

intake during pregnancy are known to have deleterious effects on the

fœtus. Therefore, mothers were asked about the number of cigarettes

and drinks taken during their pregnancy.

3.3 A D D ~ ~ ~ ~ u s

The apparatus used in collecting the data has been described

previously [68] . Each subject was tested individually in a semi-

reverberant (double-walled) IAC booth measuring 3 .4Sm x 2 .74m x 2 .2 9m

40

that conformed to ANS1 Standard (ANSI S3.1-1991) for headphone

testing. A Hewlett Packard multifuxiction synthesizer (HP 8904A) was

used to generate the pure-tone stimuli required by the experiment. The

selection of input signals and fine adjustrnent of stimulus level,

duration and envelope shaping were controlled by a Coulbourn

Instruments modular system. The speech test was commercially available

on two-track audio cassette and played using a Yamaha cassette deck

(Model: KX-W900/U). The output was fed to a pair of Hewlett Packard

manual range attenuators (Model 350D) and Rote1 integrated stereo

amplifier (Mode1 RA-1412) for presentation to the subject over a

Telephonics matched headset (TDH-49P). A Bruel & Kjaer artificial ear

(Type 4153) was used to calibrate the stimulus intensity (dB SPL) at

the earphone. Based on ANSI S3.6-1996, the reference equivalent levels

for O dB HL at 0.25, 0.50, 1, 2, 3, 4, 6, and 8 kHz are 27, 13.5, 7.5,

9.0, 11.5, 12.0, 16.0, and 15.5 dB SPL, respectively. No value is

given for 10 kHz. The audio system was controlled via an AST Prernium

286 personal computer (Model 140X) through the use of IEEE-488,

Lablinc, RS-232 interfaces, and digital 1/0 lines.

3.4 Audiometric Testing

3.4.1 Hearing Thresholds

Pure-tone thresholds were measured once in each ear using a modified

Békésy tracking procedure [68] . On each trial, a pure tone was pulsed at a rate of 2.5 pulses per second. The pulse duration was 250 msec,

including a rise/decay time of 50 msec. Subjects were instructed to

41

depress a button when the sound first became audible and to release

when the s o m d had completely disappeared. Consecutive pulses were

increased by I dB until the subject depressed the switch, after which,

pulses began to decrease by 1 dB until the switch was released.

Termination of this tracking trial occurred after a minimum of eight

alternating excursions of 4 to 20 dB. The subject's hearing threshold

was defined as the average sound level of the 8 final peaks and

valleys and was determined once for each frequency.

Consonant Discrimination

Consonant discrimination was evaluated by means of the closed set pre-

recorded FAAF test. The subject was given a typed list of 80 sets of

four monosyllabic words (consonant -vowel -consonant) . The f irst set of

40 were presented in quiet, while the second set of 40 were presented

with a background of speech-spectrum noise. For each set of 40, there

were 18 initial consonant contrasts and 22 final consonant contrasts.

One item £ r o m each set, enclosed in the phrase 'Can you

hear clearly?", was presented binaurally over the headset and the

subject was required to circle one of the possible alternatives. The

f ive available pre -recorded versions of the test were counterbalanced

across subjects.

3.5 hmroach to Data Reduction and Statistical Analvsis

Al1 data were first hand-written on data collection sheets and then

typed into Microsoft ~xcel@ spreadsheets . For threshold measurements ,

42

the hand-written values were double checked with the computer's

printer output before being entered into an Excel spreadsheet. Four

different spreadsheets were used: Threshold Data, Consonant

Discrimination Data (or FAAF Data), Screening Questionriaire Data, and

Detailed Questionnaire Data. The four spreadsheets are presented in

Appendix VII. The data outlay in these spreadsheets was modified to

accommodate SAS" software before being imported directly into SAS

(using PROC IMPORT) . Data from the detailed questionnaires were merged with that from both thresholds and FAAF scores for correlation

analysis. Once imported, these tables were stored permanently in a SAÇ

directory (SASUSER). The SAS software, running under the Windows98 8

operating system, was used for al1 statistical analyses f691.

The first step entailed examination of the data distributions and

calculation of descriptive statistics. Statistical summaries including

frequency distributions, histogxams, means, proportions and their

standard errors were obtained for al1 numeric variables. This was

achieved in SAS by using PROC UNIVARIATE with NORMAL option to test

the normality of al1 data and the FREQ procedure was used to obtain

questionnaire variable proportions.

For al1 statistical tests, significance was established as a

probability of 5% or less (a = 0.05) . The principle outcome variables were the hearing thresholds, measured in decibels sound pressure level

(dB SPL) , and the score in consonant discrimination testing, expressed

as a percentage of correct answers.

43

Repeated measures analysis of variance, using the SAS General Linear

Models procedure (PROC GLM), was used to compare means between

conditions within the group of sub j ects . For threshold measurements ,

this included difierences in thresholds between left and right ears as

well as between the nine frequency ranges tested (centred at 0.25,

0.50, 1, 2 , 3 , 4 , 6, 8, and 10 kHz). To assess the effect of

background noise on hearing, overall FAAF scores were compared between

quiet and noise conditions for each consonant position separately.

Similarly, separate analyses were performed in quiet and in noise to

assess the effect of consonant position on hearing. Al1 significant

f indings were scrutinized using the GLM options MEANS and LSMEANS to

produce Tukey' s LSD for analysis of significant interaction terms .

Because of the many possible sources of hearing loss encountered in

everyday life, and also based on questionnaire responses, factors

judged to hold greatest importance were included in the analyses.

According to the responses provided by each subject in the detailed

questionnaire, previous occurrence of ear infections was included as a

categorical (or binary) variable with 2 categories, YES or NO. Other

such categorical variables included Full term delivery , required stay

in NICU, previous occurrence of jaundice, measles, family history of

hearing problems, smoking during pregnancy, alcohol consumption duxing

pregnancy, working during pregnancy, drugs taken during pregnancy, any

medications taken by subject, any noisy leisure activities during

mother's pregnancy. Pearson correlation analysis was performed using

PROC CORR between a l 1 ratio and/or interval scale variables, including

those obtained from the detailed questionnaires. FROC FREQ was used to

44

produce 2x2 contingency tables and compute Chi-Square and Fisher's

Exact test for the analysis of categorical questionnaire variables

between each other and with 2 categories created for FAAF scores (in

noise only) by whether subjects scored above or below the group's

median. Finally, the relationship between questionnaire responses

considered as ordinal scale data (e .g . , number of alcoholic beverages consumed per week during pregriancy) and the outcome measures (interval

and ratio scale) were analyzed using Spearman correlation.

CHAPTER 4: RESULTS

Prospective subjects were al1 grade 9 and 10 students £rom six public

and private Toronto area high schools. Schools varied in location,

size of classes, and ratio of male to female students. Figure 4 - 1

shows location within the greater Toronto area, as well as type of

institution and gender-specificity. Approximately 250 screening

questionnaires were distributed at each of Parkdale Collegiate,

Loretto Abbey, Vaughn Road Academy, and St-Joseph's College. Bloor

Collegiate and Jarvis Collegiate received 297 and 500 screening

questionnaires, respectively. Of the nearly 1790 screening

questionnaires distributed, a total of 148 were returned (8%). The

response rate varied greatly across schools, with Loretto Abbey and

St-Joseph's College providing the highest number, and Bloor and Jarvis

Collegiate

4-1, along

school .

the lowest number. This information is presented in Table

with the number of students ultimately included f rom each

TABLE 4 - 1 STATISTICS ON SCHOOL PARTICIPATION

Bloor CoHegiate Jawis Collegiate Loretto Abbey Parkdale Collegiate St-Joseph's College Vaughn Road Academy

Total Returned Screening

Questionnaires N

Willingness to Participate n (% of total)

Number Admissible for study

n (% of total)

4.2.1 Screening Questionnaire

The results of the screening questionnaire will be presented under t w o

sections. One section will be devoted to information about mothers and

will include work and workplace noise exposures during pregnancy, as

well as leisure noise during pregnancy. The other section will cover

information about the students, including health status (e.g. history

of otitis media, ear surgery and head trauma), year of birth, and

gender .

d FIGURE 4 -1 LOCATION, TYPE OF INSTITUTION AND GENDER-SPECIFICITY OF THE 6 GREATER TORONTO AREA HIGH SCHOOLS SteeIes Av.

4.2.1.1 Information about Motbers

Based on the 148 screening questionnaires that were returned, it was

found that a total of 102 (69% of mothers) worked during their

pregnancy. Of these, 75% were mother of students at Bloor Collegiate,

33% at Jarvis Collegiate, 84% at Loretto Abbey, 56% at Parkdale

Collegiate, 65% at St-Joseph's College, and 58% at Vaughn Road

Academy. Workplaces, with the highest representation were office

(54%) , factory (16%) , and hospital (6%) . Six mothers (6%) terminated

their jobs after the lst trimester of pregnancy and 13 (13%) terminated

aftex the 2nd trimester. Eighty-three (81%) of the 102 mothers worked

up to and during the 3rd trimester. These data are presented in Table

4 - 2.

TABLE 4 - 2 WORKZNC STANS OF MOTHERS DURING PRECNANCY ACROSS SCHOOLS

From a total of 102 working mothers, 38 (37%) reported having been

exposed to noise at work. However, only 20 (20%) of working mothers

were considered to have been exposed to workplace noise, based on the

description of the immediate work environrnent. By school, the number

of students with occupationally exposed mothers varied as shown in

Table 4 - 3 .

TABLE 4 - 3 WORKPLACE NOISE EXPOSURES ACROSS SCHOOLS

Jarvis Loretto Collegiate Abbey

School

Parkdde Collegiate

StJoseph's College

TOTAL Vaughan Road

Academy

Noise at Work: YES NO

Not Working

I

"Considerd Occupationally

Exposed" to Noise: YES NO

Collegiate

Noisy Leisure Activities:

YES NO

Did not Answer

Total

Table 4 - 4 lists al1 of the workplace noise sources reported by 38

mothers. Among the 20 mothers who were "considered exposed to

workplace noise", 4 (21%) reported sewing machine noise, 3 (17%)

compressor-like machine

machinery noise. A total

mothers) worked until the

noise, and 2 (10%) reported assembly-line

of 1 6 (out of t he 20 occupationally exposed

3rd trimester. One mother left her employment

after the lSt trimester, and 3 mothers left their employment after the

2nd trimester. Table 4 - 5 shows which work environment had the highest number of mothers reporting noise at work.

TABLE 4 - 4 REPORTED WORKPLACE NOISE SOURCES

WORKPLACE NOISE SOURCES:

Assembly line machinery Boilers

Cornpressor Macbines Fabric Cutting Machine (ski11 saw)

Agricultural Water Guns Industrial Vacuum Cleaner

Weaving Macbines Power Tools

Pressurized Air Guns Puncbing Machines

Sewing Machines Very Loud Music

Water Pumps

Typical Noises (typewriters, printers, talking, telephones, copy machines, restaurant kitchen

noises like dishwashers, hospital patient monitors such as heart monitors, children talking in the

classroom, etc.)

% of Mothers Reporting Noise

Source

Factory Warehouse

Office Laboratory

RestauraatfHotel Outside

Jewellery Shop Hospital

Clothing Store House

Shopping Mall Grocery Store

Photo Studio Gymnasium

Number of motbers reporting noise at work

Fifty-six of the 148 mothers (38%) reported being exposed to

recreational (or leisure) noise sources during their pregnancies.

Mothers reporting recreational noise made up 13% of al1 respondents

£rom Bloor Collegiate, 33% of a l 1 respondents from Jarvis Collegiate,

31% of al1 respondents from Loretto Abbey, 56% of al1 respondents from

Parkdale Collegiate, 44% of al1 respondents from St-Joseph's College,

and 36% of al1 respondents from Vaughn Road Academy. Table 4 - 6 lists

al1 the reported sources of leisure noise during pregnancy. It is

important to note that each mother could report numerous sources of

leisure noise. Hence the percentages do not add up to 100 across ail

categories (sources) . The amount of tirne mothers reported having been

exposed to recreational noise sources are shown in Table 4 - 7. It is

interesting to note that 21 out of 102 working mothers (21%) reported

both workplace noise and recreational noise. Twelve (60%) of the 20

mothers "considered occupationally exposed to noise" also reported

engaging in noisy recreational activities.

SOURCES OF LEISURE NOISE DURING PREGNANCY

Auto Racing Disco/Dance Bars

Guns Use of Headphones

Music andfor Concerts Motorized Vebicles

Musical Instruments Power Tools

Sewing Machine Typical Noises (Television, talking,

bingo, city traffic, etc.) Not Specified

% of Mothers Reporting Leisure

Noise Source (N=59)

2% 29% 3% 17% 42% 17% 3% 17% 2% 11%

2%

TABLE 4 - 7 TIME EXPOSED TO REPORTED LEISURE NOISE SOURCES

AMOUNT OF TIME EXPOSED TO LEISURE NOISE DURXNG PREGNANCY

O to 5 Hours per Week 6 to 10 Hours per Week

11 to 20 Hours per Week 21 to 30 Hours per Week

More than 30 Hours per Week

% of Mothers Reporting Leisure

Noise Source (N=59)

4.2.1.2 Information About the Students

Across schools, 87% of al1 student respondents were fernale, This was

because two of the six schools only enrolled fernales. In the four

mixed-gender schools, 41% of respondents, on average, were female.

Gender distribution among schools is shown in Table 4 - 8.

ABLE 4 - 8 STUDENT GENDER DlSTRIBllTION AMONG SCHOOLS

I I SCHOOL:

Unspecified Gender

Bloor Collegiate Jarvis Collegiate

Loretto Abbey School Parkdale Collegiate St-Joseph's College

Vaughan Road Academy

Total Nurnber of

Respondents

Number of Female

Respondents

Student health information is shown in Table 4 - 9. Thirteen (9%) of

148 students were born prematurely. Bloor Collegiate and St - Joseph's

College accounted for the highest proportion of premature births, with

25% of respondents from Bloor Collegiate and 13% of respondents from

St-Joseph's College. Thirty-four students (23%) of 148 had had otitis

media during childhood. An additional 8% had had ear surgery. One

student, from St-Joseph's College, reported having experienced head

trauma.

Number of Male

Respondents

3 1

38 3

78 5

5 2 O 5 O 6

I F5ALTH INFORMATION

Bloor Collegiate

Premature Birth: YES NO

No Answer

Ear Surgery:

No Answer

2 6 O

Ear Infection History :

YES NO

No Answer

Head Trauma: YES NO

No Answer

1 7 O

Total 18

Jarvis Collegiate

Loretto Abbey School

--

ParMale Collegiate

- -

StJoscph's Vaugban TOTAL College Road

Academy

According to school, the number of subjects included in this study

ranged from 1 to 14 (see Table 4 - 1) . Out of the 20 mothers

'considered exposed to workplace noise", only 10 were willing to

participate in the study and 5 initially met the selection criteria

and were tested.

4.2.2 Detailed Ouestionnaire

In the detailed questio~aire, answers from both mothers and subjects

are presented together as they more accurately represent the lifetime

risk for hearing loss in adolescents i . , from the onset of

pregnancy). Answers were classified according to the nature of the

risk factor such as noise, dnigs (including alcohol and tobacco) , and

the general health of subjects and mothers during their pregnancies .

Noise was furthex subdivided in two sections, namely, workplace noise

reported by the mothers and al1 recreational noise sources for both

subjects and mothers. Health information includes age of subjects at

testing, age of mothers at parturition, subject's gender, premature

birth, birth weight, number of siblings. It also includes subject's

illnesses such as ear infections , ear surgery, j aundice, measles,

meningitis, and rnother's illnesses during pregnancy such as rubella

and herpes, as well as family history of hearing problems and head

trauma.

4.2.2.1 Health Information

The 26 subjects included in the study ranged in age from 14 to 16

years , with an average age of 14.7 years (SD = 0.79) . Half were 14

years of age, while 31% were 15 years, and the remaining 19% were 16

years of age at testing. Neither age nor gender were considered as

covariates in the analysis of the objective test outcornes (i.e.,

hearing threshold and consonant discrimination). Figure 4 - 2 shows

the age and gender distribution of these 26 subjects.

FIGURE 4 - 2 SUBJECT GENDER AND AGE DISTRIBUTION (Ne26)

Fernale Male

GENDER

58

Al1 but two of the subjects' mothers were between 25 and 35 years of

age at parturition. The remaining two were 39 and 40 years of age. Al1

subjects, with the exception of two, were full term births. Those born

prematurely were 5 and 6 weeks early. Birth weights ranged from 3

pounds to approximately 9% pounds, with 85% of subjects situated

between 5 and 9 pounds. Figure 4 - 3 shows the birth weight

distributions for both full term and prernaturely born subjects. Two

subjects reported having spent time in a neonatal intensive care unit

(NICU) .

FIGURE 4 - 3 SUBJECT BIRTH INFORMATION (Nt26)

hrth Weight: = 7 LBS

, Blrth Wight: s 6 Lm

&th Weight: 2 8 LBS

None of the mothers reported having had rubella or herpes during their

pregnancy. Approximately half of the subjects (n = 13) reported having

suffered from otitis media at least once. None of the subjects ever

contracted bacterial meningitis or had mumps. However, two subjects

did report having had jaundice while another reported having had

measles.

Sometimes ear infections will occur in many members of the same

family. In this study, 23 subjects (i-e., 89%) said that they had

siblings. A total of 4 out of these 23, reported that one or more of

their siblings had experienced otitis media. Interestingly, these 4

subjects had not, themselves, ever suffered from otitis media.

Two subjects, from the 26 subjects, reported hearing difficulties in

one or both of their paternal grandparents, while six subjects

reported hearing difficulties in one or both of their maternai

grandparents . Most of these problems were either age or work-related.

Four subjects reported that their fathers had hearing difficulties,

rnostly due to occasional otitis media, although one was work-related.

The only subject who reported that her mother experienced otitis media

had, herself, experienced otitis media. The data for otitis media

history and family history of ear problems are presented in Table 4 -

10.

TABLE 4 - 10 SUBJECT HEALTH INFORMATION FROM DETAILRD QUESTIONNAI^ R E S m N S m

SUBJECT HEALTH INFORMATION FROM DETALLED QUESTIONNAIRE

OTITIS MEDIA EIISTORY: YES NO

- -

FAhLILY HEARLNG PROBLEMS: None

Mother Fathe r

Materna1 Grandparents Paternal Grandparents

Sibüngs

4.2.2.2 Mother's Workplace Noise

A total of 18 (69%) of 26 mothers worked during their pregnancies. Al1

of them worked during their first trimester, with 2 (11%) and 5 (28%)

leaving their employment after the first and second trimesters,

respectively. Therefore, only 62% of al1 working mothers remained at

their jobs throughout the third trimester. Out of the 18 working

mothers, a total of 10 reported having been exposed to noise at work

as is shown in Table 4 - 11. However, based on the description of the

woxk environment, only 3 out of these 10 mothers were 'considered

occupationally exposed to noise". Table 4 - 11 also shows the amount

of time mothers reported having been exposed to noise at work as well

as the loudness of the noise.

TABLE 4 - II MOTHER'S WORKPLACE AND WORKPLACE NOISE

WORK AND NOISE DURING PREGNANCY

. - --

WORKING WHILE PREGNANT: NO

Office Hospital Fac tory Ou tside

Restaurant

WORK AREA REPORTED AS NOISY?: YES NO

AMOUNT OF TIME WORK -A WAS 1 NOISY (al1 mothers reporting noise at work):

SELDOM (>1/4 of time) SOMETIMES (1/2 of time)

OFI'EN (>3/4 of time)

REPORTED LOUDNESS OF NOISE AT WORK (al1 mothers reporting noise at work):

LOW/MILD MEDIUMIMODERATE

HIGHISEVERE

MOTHERS CONSIDERED OCCUPATIONALLY EXPOSED:

YES NO

% of Total N W=W

Mothers who were 'considered occupationally exposed to noise" reported

moderate to severe noise levels. Two of the 3 mothers 'considered

occupationally exposed to noise" worked in the textile industry and

reported a factory-setting immediate work environment. One of thern

63

worked as a 'cutter" on a floor with many sewing machines and spent

hours at a time using a fabric cutting machine, which she reported to

be very noisy. A second mother worked in a factory that made service

uniforms and reported working at the presses where thcre were

compressor-like noises. She reported being exposed to noise at work 35

of the time (sometimes), while the 'cutter" reported being exposed

more than X of the time (often) . The third woman worked on a farm in India. In addition to farm machinery, she reported noise cxposures

frorn frequent aircraft (helicopters) and military weapons (guns), as a

war was being fought. She reported being exposed about half of the

time to al1 these noises when at work and perceived the loudness to be

severe . Two of these three noise-exposed mothers worked throughout

their 3rd trimester of pregnancy, while the third (the one who worked

as a "cutter") terminated her job after her second trimester.

TABLE 4 - 12 OCCUPATIONALLY EXPOSED MOTHERS

Exposed Textile Factory mother #1

Exposed Textile Factory mother #2

Exposed Outside (Farm) mother #3

Noise Sources

i) Fabric cutting machine ii) Sewing machines

i) Compressor-like machine ii) Sewing machines

i) Farm machinery ii) Heticopters iii) Guns

Time exposed to noise sources

more than 3/4 of the time

!4 of the time

!4 of the time

Perceived Loudness

Moderate

Moderate

Severe

The remaining 7 mothers reporting noise described more "cornmon" noise

sources at work. Such common noise sources may be described as sources

often encountered in everyday life and not regarded as being hazardous

to the worker due to the low noise levels i . . , below 85 dBA) . Even

though these sources do not constitute "occupational noise", they may

have had some other type of physiological effect on the mothers

reporting them (i.e. increased stress levels, elevated blood pressure,

etc.). Four of the 7 mothers reported that the noise occurred less

than X of the time (seldom) and perceived the loudness to be mild with

the exception of one mother reporting moderate noise levels. The

remaining 3 out of 7 stated that their workplace was noisy more than 34

of the time (often) at moderate levels with the exception of one

mother who perceived the loudness to be mild. When taking into account

al1 10 mothers who reported noise at work, Fisher's exact test did not

reveal any statistically significant association between perceived

loudness of noise at work and type of workplace noise (i.e.

"occupational" versus ncommonm ) . Nei ther were there any s tatistically

significant associations between amount of time a work area was noisy

and the perceived noise loudness. In other words, loud noises were

just as likely to have lasted for short time periods as they were to

have lasted for long time periods.

65

TABLE 4 - 13 MOTHERS REPORTINC NOISE AT WORK (WHO WERE NOT "CONSIDERED OCCUPATIONALLY EXPosED TO NOISE?

Mother

1

2

3

4

5

6

7

Hospital

Hospital

Hospital

Hospi ta1

Office

Office

Office

Reported workplace noise sources

i) paging/loud speakers ii) people shouting iii) moving tiuniture/heavy equipment

i) people shouting ii) moving fiirriitureheavy equipment iii) fans

i) people shouting ii) noisy medical equipment

(e-g. ECG monitors)

i) moving furnitureheavy equipment ii) fire alanns

i) people shouting ii) moving fumiture/heavy equipment

i) crowds talking

i) typewriter noises

Amount of time exposed

more than % of the tirne

less than '/s of the time

more than ?4 of the time

less than Yi of the time

more than ?4 of the time

less than !4 of the time

less than !Li of the time

Perceived Loudness

moderate

moderate

mild

mild

moderate

mild

4.2.2.3 Recreational Noise Sources

Eighteen of the 26 subjects (69%) reported being exposed to noise £rom

recreational activities. A t o t a l of 8 sources of leisure noise were

reported and are listed in Table 4 - 14. Of these subjects, 78%

reported being exposed to at least 1 or 2 of the listed sources. Three

subjects (18%) reported exposures £rom up to 3 and 5 sources of

leisure noise, while one subject was exposed to 7 recreational noise

sources. Al1 but 2 of the listed sources involved various forms of

music (e .g., amplif ied, voice, instrumental) . Furthemore, 62% of a l1

66

subjects reported listening to amplified music with stereo headphones.

Table 4 - 15 shows al1 the listed noisy recreational activities

reported by the subjects' mothers in the detailed questionnaire.

LBLE 4 - 14 SuBJECiS' NOISY HOBBIES

SUBJECT INFORMATION 1 FROM QUESTIONNAIRE

RESPONSES

PLAYING MUSIC IN A BAND: YES NO

ATTENDED ROCK CONCERTS: YES NO

USE STEREO HEADPHONES: YES NO

OTHER NOISY HOBBIES: Don't Know

Noue Loud music on Hi-Fi or Cornputer

Choir Singing Playing the Piano

Aircraft (air cadets) 'Skateboarding'

% of Total N

A total of 7 mothers reported having been exposed to recreational

noise sources during their pregnancies. Four of them reported having

been exposed, concurrently, to 3 different sources of leisure noise-

Additionally, 2 of them reported having engaged in these activities

67

from 6 to 10 hours per week. One mother reported engaging in her noisy

hobbies from 11 to 20 hours per week, while another mother reported

having been exposed to her noisy leisure activities for more than 30

hours per week. The remaining mothers, on the other hand, only

reported one noisy hobby. Two of these mothers reported engaging in

their recreational activity for less than 5 hours per week, while the

other mother reported engaging in her activity £rom 6 to 10 hours per

week. The leisure noise sources most often reported were soft (non-

rock) music and power tools, as represented in Table 4 - 15.

TABLE 4 - 15 REPORTED NOISY RECREATIONAL A(TIVITIES OF MOTHERS DURING PREGNANCY

NOISY LEISURE ACTIVITIES DURING PREGNANCY

NOISY LEISURE ACTIVITIES DURING PREGNANCY:

YES NO

TYPES OF NOISY HOBBIES: Rock Music

Other Music Disco/Dance Bars

Power Tools Motorcycles

Guns Other

AMOUNT OF TIME EXPOSED TO LEISURE: NOISE SOURCES:

0-5 hrs/week 6-1 0 hrslweek

11-20 hrdweek More than 30 hrs/week

% of Total N

w=2a

27% 73%

8% 12% 4% 12% 8% 4% 12%

8% 12% 4% 4%

4.2.2.4 Drum. Alcobol, and Tobacco Consum~tion

Seventeen out of twenty-six subjects (65%) reported having been

prescribed various medications. Table 4 - 16 shows which drug classes

were prescribed to these subjects . Antibiotics (various families)

comprised 64% of al1 prescription medication taken by subjects. Five

mothers also reported taking drugs during their pregnancy. Two of

these mothers reported having been prescribed antibiotics during their

pregnancy and one reported having been prescribed antiemetics (for

morning sickness). The remaining 2 reports of medication concerned

over- the -couriter (OC) drugs . One mother reported having taken various

analgesics, while another could not remember precisely which OC

medication she might have taken during her pregnancy.

None of the reported drugs were known ototoxic agents, except for the

over-the-counter pain killer , acetylsalicylic acid, which in high

doses is known to cause tinnitus. However, such doses were not

suspected here. Additionally, other non-ototoxic pain killers, such as

acetaminophen, were often pref erxed .

TABLE 4 - 16 DRUGS REPORTED BY SUBJECïS AND MOTHERS DURING PRECNANN

DRUCS REPORTED BY MOTHERS AND SUBJECTS:

DRUGS TAKEN BY MOTHER DURING PREGNANCY:

None An tibio tics

Antiemetics (for morning sickness) Analgesics Unknown

PRESCRIPTION DRUGS TAKEN BY SUBJECT:

None Penicillins

Tetracyclines Corticosteroids

P-Agonists An tic holinergics

Antibiotics (unknown names) NSAïDS

Isotretinoin

% of Total N

A total of 2 mothers reported having smoked tobacco during their

pregnancy, while 5 mothers reported having consumed alcohol during

their pregnancy. However, there were no mothers who reported both

tobacco and alcoho1 intake during pregnancy. The highest reported

amount of alcohol intake w a s approximately one dink per day, while

none of the mothers reported smoking more than a pack pew day (about

10 cigarettes). Figure 4 - 4 shows alcohol intake during pregnancy for

al1 26 mothers.

FIGURE 4 - 4 ALCOHOL INTAKE DURING PREGNANCY (N=26)

Nurnber of Mothers

week

Number of Drinks

4.3 Psvchoacoustic Results

4.3.1 Hearing Thresholds

The results of the audiometric testing are presented in Table 4 - 17.

Mean hearing thresholds are given in dB SPL for the nine frequencies

tested and in dB HL for eight of the nine tested frequencies (i-e.,

from 0.25 to 8 kHz) . The conversion from dB SPL to dB HL was

detemined using reference equivalent values given in ANS1 standard

S3.6-1996 for the Telephonics (TDH-49P) headset [681 .

TAULE 4 - 17 PURE-TON€ HEARINC THRESHOLDS (dB SPL) AND CORRESPONDING HEARlNC LEVELS (dB m) OBTAINED WITH THE TDH49P HEADSET IN N=26 TEENAGERS

Frequency

250 500 1 O00 2000 3000 4000 6000 8000 10000

5 4 3 O -2 -3 -2 -1

NIA

Right Ear Thresholds Hearing Level Mean (SD) Conversion (dB SPL) [a HL]

4 O O -2 -3 -1 -2 2

NIA

Left Ear Thresholds Hearing Level Mean (SD) Conversion [dB SPL] (dB HL]

Threshold differences between ears, across individuals, varied from O

to 31 dB SPL. For some frequencies, although the ear difference may

have been more than zero, no ear was worse (overall) then the other

72

(e-g., if 6 individuals had a 12 dB difference between their ears at a

particular frequency with 3 of them have worse hearing in the left ear

and 3 in the right ear, no ear was worse overall). The results are

shown for each tested frequency in Table 4 - 18.

TABLE 4 - 18 THRESHOLD DIFFERENCES BETWEEN EARS (LEFT - RIGHT) ACROSS INDIVlDUALS AT EACH OF THE TESTED FREQUENCIES

Frequency (az)

Minimum Ear Difference

(dB SPL)

Maximum Ear Differeoce

(dB SPL)

Worse Ear

Overall

Right Right Right Lef? None None Left Le fi

Right

Figure 4 - 5 shows a plot of mean hearing thresholds as a function of

frequency for the left and right ears. A repeated-measures ANOVA was

applied to the data to test the effects of ear and frequency on

hearing thresholds [69]. The results are shown in Table 4 - 19. There

w e r e statistically significant effects of ear and frequency, as well

as significant effects of frequency by ear.

FIGURE 4 - 5 MEAN HEARING THRESHOLDS AS A FUNCTION OF FREQUENCY FOR RIG HT AND LEFT EARS (IN 26 SUBJECTS)

L E F T €AR 1

- + - RlGHT EAR

TABLE 4 - 19 REPEATED MEASUMS ANOVA ON THRESHOLD DATA

Pairwise cornparison of means for combination of levels in the

interaction term were performed using the Tukey-Kramer adjustment.

Statistically significant differences in threshold between frequencies

in the right ear included the 250 Hz thresholds versus al1 other

thresholds. Differences between the 250 Hz frequency ranged £rom 13 dB

SPL with the 8000 Hz (p < 0,0001) frequency to 23 dB SPL with the 1000

and 2000 Hz frequencies (both p c 0.0001).

Source of Variation

Ear

Frequency

Frequency*Ear

Error

Pairwise cornparisons of thresholds for each ear by frequency revealed

statistically significant differences at the 500, 1000, 8000, and

10000 Hz frequencies. Differences in hearing thresholds between ears

are presentcd in Table 4 - 20. For al1 cases, in the right ear,

thresholds were higher ( e t hearing was worse) than the left ear,

with the exception of the 8000 Hz frequency for which the left ear

thresholds were higher than the right ear thresholds.

DF Type 1 SS Mean Square F P

1 1 19.84 1 19.84 4.06 0.0446

8 20950.20 26 18.78 88.63 < 0.001

8 734.79 9 1.85 3.1 1 0.002

424 12527.91 29.55

TABLE 4 - f 0 STATISTICALLY SICNIFICANT HEARINC THRESHOLD DlFFERENCES BETWEEN EARS FOR SPECIFIC FREQUENCIES

4.3.2 Consonant Discrimination

Frequency (Hz)

Table 4 - 21 shows results from the consonant discrimination test in

quiet and in a noisy background, presented separately for final and

initial consonant positions. The FAAF scores are expressed as the

percentage of correct answers.

TABLE 4 - 21 CONSONANT DISCRIMINATION (FAAF TEST) RESULTS FOR N=26 SUBJECTS

Difference (Left-Right) between mean thresholds (dB SPL)

Listening Condition L NOISE

P

Initial Consonant Score (%) Final Consonant Scores (%)

Mean (SD) Min Max Mean (SD) Min Max

Total Score

97.4% (1.9)

72.5% (6.0)

A repeated-measures ANûVA was applied to the results of the FAAF test.

Outcornes are presented in Table 4 - 22. The analysis revealed

statistically significant efiects of listening condition (quiet versus

noise) and consonant position, as well as effects of listening

condition by consonant position.

TABLE 4 - 22 REPEATED MEASURES ANOVA ON FAAF SCORES

Source of Variation

Listening condition

Consonant position

Listening condition*Consonant position

Error

DF Type 1 Mean F P SS Square

1

Pairwise analysis (using the Tukey-Kramer adjustment) of the

interaction term revealed a sigriificant difierence in scores according

to consonant position for the speech-spectrum noise background. In

noise, the ability to correctly identify final consonants was 10% îess

than the ability to correctly identify initial consonants (p É

0.0001). However, no statistical difierence between consonant

recognition scores was found in quiet (p = 0.7324) . Additionally, a statistically significant difference in scores between listening

conditions for both initial and final consonant positions were found.

The ability to discern final consonants decreased by 28% (p c 0.0001)

77

in a noisy background, while the ability to discern initial consonants

decreased by 21% (p < 0.0001) in a noisy background. Figure 4 - 6

shows a plot of FAAF scores as a function of consonant position, for

quiet and noisy listening conditions.

FIGURE 4 - 6 MEAN INITIAL AND FINAL CONSONANT SCORES IN QUIET A N D IN SPEECH-SPECTRUM NOISE (IN 26 SUBJECTS)

CONSONANT POSKION

4.3.3 Correlations

4.3.3.1 FAAF and Threshold Correlations

The relationship between FAAF scores in noise, for both initial and

final consonant positions, and hearing thresholds was assessed using

Pearson correlation analysis. Correlations were performed with hearing

thresholds at O -5, 1, 2, 3, and 4 kHz for both left and right ears

separately. The only statistically significant correlation coefficient

was that for the 3000 Hz hearing threshold in the left ear and the

initial consonant discrimination score in noise (r = -0.40, p = 0 . O 4 ) .

The poorer the hearing, the lower the percent correct.

4.3.32 FAAF and Ouestionnaire Data Correlations

Depending on the nature of the questionnaire variables, either

Spearman correlation (ordinal data) or Fisher's exact test

(categorical data) were performed with initial and final FAAF scores

in noise. Two-by-two contingency tables were constructed with

categorical questionnaire data and FAAF scores in noise. The initial

and final FAAF scores were categorized according to whether the

subject scored above or below the group median. Those with scores

equal to the median value were considered to have scored above the

median. The contingency tables for selected categorical questionnaire

data are presented in Tables 4 - 23 to 4 - 28. Those questionnaire

variables with highly uneven numbers of subjects (e.g. 2 categories

with 3 subjects in one category and 23 in the other) were not

analyzed.

TABLE 4 - 23 CONTWGENCY TABLE FOR OTtTtS MEDIA HISORY AND FAAF SCORES LN NOISE

OTITES MEDIA HISTORY

Initial Consonant Score

Below Above Median (a) Median (n)

YES NO

STATISTIC: 1 Fisher = 0.3 1 Fisher = 0.3

Final Consonant Score

Below Above Mediaa (a) Mediao (a)

TOTAL (N)

1 NaS. 1 N.S.

Total k 5 8 5 8

TABLE 4 - 24 CONTCNGENCY TABLE FOR MOTHER'S WORK DURlNC PREGNANCY AND SUBJECT'S F u SCORES

10 16

IN NOISE

4 5 8

9 17 lm

WORK DURING PREGNANCY

YES NO

TOTAL (N)

STATISTIC: F

1 : : I

Fisher = 0.2 N.S.

Total r Initial Consonant Score

Below Above Mediaa (n) Median (n)

6 12 4 4

10 16

Fisher = 0.3 N.S.

Final Consonant Score

Below Above Median (n) Median (n)

6 12 3 5

9 17

81

TABLE 4 - 25 CONTINCENCY TABLE FOR NOISE AT MOTMER'S WORK AND StiRfECT'S F A N SCORES IN NOISE

For N=18 Workin~; Mothers Reported ooise at work?

TOTAL (N)

7 STATISTIC:

Initial Consonant Score

Below Above Median (n) Median (n)

Fisher = 0.3 N.S.

Median (n) Median (n)

3 7 3 5

Fisher = 0.4 *.S. 1

TABLE 4 - 26 CONTINCENCY TABLE FOR MOTHER'S NOISY HOBBIES DURING PREGNANCY AND SUWECT'S FAAF SCORES IN NOISE

II NOISY HOBBIES DURING PREGNANCY

YES NO

TOTAL (N)

STATISTIC: II

Initia1 Consonant Score

Below Above Median (n) Median (n)

Final Consonant Score Total

Below Above Median (n) Median (n)

3 4 6 13

Fisher = 0.3 Fisher = 0.3 NS. NoSm

TABLE 4 - 27 CONTINCENCY TABLE FOR SUBJEClS PLAYING MUSIC IN A BAND AND FAAF SCORES IN NOlSE

SUBJECT PLAYS MUSIC IN A BAND

YES NO

TOTAL (N)

Fisher = 0.3 N.S.

STATISTIC:

ABLE 4 - 28 CONTINGENCY TABLE FOR SUBJECîS LISTENING TO MUSIC WlTH EARPHONES AND F l NOISE

I I

Initial Consonant Score Below Above

Median (a) Median (O)

3 5 7 11

10 16

Fisher = 0.3 N.S.

Initial Consonant Score SUBJECT LISTENS Below Above TO MUSIC WITH Median (n) Median (O) EARPHONES

Final Consonant Score Total Below Above

Median (n) Median (n)

3 5 6 12

9 17

mm Final Consonant Score

Below Above Median (O) Median (n)

TOTAL (N) 10 16 9 17

I STATISTIC: Fisher = 0.3 1 N.S.

Fisher = 0.3 l N.S.

Total

10

When looking at ordinal questionnaire data (i.e. where responses

represented a 'grading" f rom least bad to worse) , Spearman correlation

was performed .

83

Al1 the rnothers who either did not work or did not report noise at the

workplace were included in the "I=Neverm category for the amount of

time exposed to workplace noise. The results were not significant

(Initial: x = 0.0, p = 0.9, Final: -0.3, p = 0.2). Similarly non-

working mothers and mothers not reporting noise at work were included

in the "l=Not Noisy" category for the grading of loudness for noise at

work. There were no significant findings ( Initial r = -0.1, p = 0.5,

Final: r = -0.2, p = 0.2). However, when including only those mothers

who reported noise at work (i .e. rernoving al1 the non-working mothers

and those not reporting noise at work) there were only 10 mothers.

Performing a Spearman correlation revealed a significant correlation

between final FAAF scores in noise and perceived loudness of noise at

work ( r = -0.8, p = 0.002). Among the 10 subjects with mothers who

reported noise at work, only one reported workplace noise loudness as

'severe' . This particular subject obtained the lowest score (45.5%)

for final consonant discrimination and the second lowest score (66.7%)

for initial consonant discrimination in noise. Even with the removal

of this subject, there was still a strong association of the "loudness

of noise at workf variable with final consonant discrimination scores

in noise (r = -0.702, p c 0.03).

4.3.4 Effects of otitis media on hearine thresholds and FAAF scores in noise

Initially, subjects were divided in 2 groups according to history of

otitis media (n = 13) and included in a 2-way ANOVA (by otitis media

group) with repeated-measures on 2 factors (ear and frequency) .

Results from the analysis are pxesented in Table 4 - 29. As in the

repeated-measures ANOVA (Table 4 - 19), there were statistically

signif icant ef f ects of otitis media history (p = 0.011) , ear (p <

0. OS), frequency (p c 0.0001) , and a signif icant interaction of ear

and frequency (p = 0 -002) . However, there were no significant

interactions with otitis media.

TABLE 4 - 29 SIGNIFICANT MlXED DESIGN REPEATED-MEASURES ANOVA RESULTS FOR HEARLNG THRESHOLDS, ACCORDLNG TO OTlTlS MEDIA HISTORY

Source of Variation

Otitis Media Ear Ear* Otitis Media Frequency Frequency* Otitis Media Frequency*Ear Frequency*Ear* Otitis Media Error

Type 1 SS

There were no significant differences in FAAF scores according to

otitis media history . There were also no signif icant interactions

between otitis media and listening condition nor consonant position.

CHAPTER 5: DISCUSSION

5.1 Hearine levels

According to Yantis [701 and Niskar et al [41 , normal hearing in

teenagers and young adults is defined as hearing thresholds within the

range of -10 to 15 dB HL. Slight hearing loss is defined as thresholds

within the range of 16 to 25 dB HL and mild hearing loss is defined as

thresholds within the range of 26 to 40 dB HL. In the present study,

group hearing levels did not exceed 15 dB HL at any frequency.

However, unilateral hearing levels in excess of 15 dB HL were observed

at 0.25, 0.5, 6, and 8 kHz in £ive individuals (19%). Two subjects

(8%) had a slight hearing loss at the individual frequencies of 0.25,

C . 5 , and 6 kHz. One subject had a slight loss at 0.25 kHz in the worse

ear, another at O. 5 M z in the worse ear, while another had a slight

loss at 6 kHz in the worse ear. Finally, two subjects (8%) had a mild

hearing loss (both 26 dB HL) at 8 kHz in the worse ear.

Hearing in young subjects, between the ages of 9 and 16 years, was

also measured in a study by Margolis et al [53 1 . Thresholds from 0.25

to 8 kHz were measured in dB HL. However, the 10 kHz thxesholds were

measured in dB SPL. Thresholds are compared between the Margolis [531

studyfs control group and better hearing sub-group (chapter 2, section

2.3) with those of the present study in Table 5 - 1. Al1 thresholds

represent the average hearing threshold for both ears. Threshold

dif ferences ranged from 2.4 to 3.5 dB and thus cannot be considered

clinically significant (i-e., too small for "true" difference) 1711.

TABLE 5 - 1 COMPAREON OF HEARiNG THRESHOLDS EN dB BETWEEN THIS STUDY (2000) AND THE MARGOLIS !XUDY (2000) (53) AVERAGED ACROSS LEiW AND RIGHT EARS

Frequency

0.25 0.5 1 2 4 8

Margolis et al (53) (2000)

Better Hearing Group Mean (SD)

Presea t S tudy (2000)

Mean (SD)

Margolis et al (53) (2000)

Control Group Mean (SD)

2.5 (2.6) 4.2 (3.6) 4.2 (1 -9)

-1.7 (3.9) 0.4 (4.5) 4.6 (8.4)

Lopponen and coworkers [72] also studied hearing in £ive different age

Il

groups of males and females. Hearing thresholds (in dB SPL) fxom the

15 year old female group (N = 14) in the Lopponen study [72] are

10

compared to thresholds from females in the present study (N = 22) in

15. 1 (9.3) dB SPL . -

Table 5 - 2. Al1 threshold values represent the average from both

1 7.5 (9.2) dB SPL

ears .

TABLE S - 2 COMPARISON OF HEARlNC THRESHOLDS IN dB SPL BETWEEN FEMALES FROM THE PRESENT STUDY (2000) AND THE LOPPONEN STUDY (1991) [721 FEMALE CROUP, AVERAGED ACROSS LEFT AND WGHT EARS.

Frequency (Hz)

Current Study (2000) Mean Thresholds (dB SPL)

Lopponen et al (1991) (721 Mean Thresholds (dB SPL)

Results are similar for the 0.5 to 4 kHz frequencies but begin to

diverge from 6 kEIz onwards - Although the difference is not clinically

relevant [71] at 6 M z , it becornes more important at 8 and 10 M z with

differences of 12 and 14 dB respectively. Nevertheless, differences

between thresholds in the Lepphen study [72j and the present study

may be explained by variations in equipment and testing methods

between the Lbpponen study [72] and the current study. The Lopponen

study [72] included 14 female subjects while the present study counted

a total of 22 female subjects. This difference in number of subjects

may also account for some of the observed threshold differences.

Heaxing thresholds from this study were also compared to thresholds

£rom the Burén study [78] in Table 5 - 4. The Burén study group was

very similar to the present study group. Burén tested 94 teenagers

with the same age range as the present study and had a similar mean

age (Burén 14.6 years, present study 14.7 years) . Subj ects with ear

wax were also excluded from their analysis. Burén inspected al1 the

ears for signs of a pathologie otoscopy rather than ask for ear

disease history in a questionnaire, as was done in the present study.

They considered answers to this question would be unreliable in this

age group. However, in the present study, the mothers filled out the

questionriaires and thus information regarding the subject's history of

ear disease was expected to be reliable. Al1 values £rom 0.25 to 8 kHz

in Table 5 - 4 are given in dB HL, while the values for 10 kHz

frequency are given in dB SPL. Each value represents the average

threshold of both ears.

88

TABLE 5 - 4 COMPARJSON OF HEARlNG THRESHOLDS lN dB HL BETWEEN THIS STUDY (2000) AND THE BURÉN !SïUDY (1992) (781 AVERACED ACROSS LEET AND RlCHT EARS

10000 1 29.4 (1 0.5) dB SPL 1 S. 1 (9.3) dB SPL

Frequency (Hz)

None of the threshold differences in the standard audiometric

frequency range (0.25 to 8 kHz) can be considered clinically

significant. The 10 H z thresholds were 14.3 dB lower in the present

study. However, such variation could be explained by different

equipment (e . g . , type of earphones , audiometer) and test ing procedures

between the Burén study and the present study.

Burén et al (1992) [78] Study (2000) MEAN (SD) N+4 MEAN (SD) N=26

According to our criteria for "normal hearingw, thresholds for the

present study and those by Margolis [53] , Lepphen [72] , and Burén

[ 7 8 ] do not indicate any hearing loss, on average, in young teenage

subjects. Comparison of results from these three studies, as expected,

did not reveal any clinically significant deviations [721 from results

in the present study.

5.1.1 Hearing in teenagers corn~ared to hearing in Young adults

Hearing acuity and sound localization are known to deteriorate with

increasing age [75] . Hearing acuity decreases initially in the high frequencies and then progresses to affect the lower frequencies [731 . Children have better hearing acuity in the high frequencies,

especially in the extended high-frequencies [79]. From the early fœtal

stages (see chapter 2 ) , hearing acuity starts to increase and reaches

a maximum, after which it gradually begins to deteriorate. Trehub et

al [74] used sound localization to determine absolute auditory

sensitivity (acuity and localization) in children and adults. Their

hearing thresholds were equal to the intensity of the test signal that

would produce a 65% correct localization score. This 'absolute

sensitivity" reached a maximum by the age of 10 years for stimuli from

0.4 to 1 kHz, and at the age of 8 years for stimuli at 2 and 4 kHz. No

change was noted at 10 kHz after the age of 4 or 5 years. For stimuli

at 20 kHz, the maximum sensitivity was reached at 6 to 8 years,

followed by a progressive decline in sensitivity to levels measured in

adults. It is important to note that these tests were actually dealing

with sound localization and that auditory sensitivity may have

reflected the age-related changes in encoding binaural and spectral

cues [75] rather than age-related hearing acuity.

Hallmo et al [76] found an increase in thresholds for the high-

frequencies (8-16 kHz) £rom adolescence to adulthood. They noted

significant difierences in thresholds £rom 13 to 20 kHz between their

8-14 year old group and their 18-24 year old group. However,

thresholds at 10 kHz did not difier between these 2 groups.

In Table 5 - 5, results from the present study are compared to those

of a study by Abel et al [73] which used the same testing facility and

protocols for measuring hearing thresholds in subjects aged 20 to 39

years. The only clinically relevant [71] threshold difierence is found

at 10 kHz in the left ear only. However, comparison of results from

the Abel study [73] and the present study provides no evidence to

support any significant decline in hearing from adolescence to

adulthood at 0.25 to 10 kHz.

TABLE S - S COMPARISON OF HEARING THRESHOLDS (IN dB SPL) BEîWEEN THE PRESENT m D Y (IV=%) f AND THE ABEL m D Y (731 (N=2O) ACCORDINC TO EAR.

'f' N=2S for ngbt ear at 10 kEIz

Frequency (Hz)

250 500 1 O00 2000 3000 4000 6000 8000 1 O000

Right Ear -

Present Study Abel el al [73] (2000) (2000)

Mean (SD) Mean (SD)

32 (5) 25 (4) 17 (4) 12 (5) 11 (5 ) 7 (6) 9 (5) 9 (5 ) 9 (5) 13 (6) 9 ( 9 13 ( 5 )

14 (6) 17 (8) 14 (5) 20 (1 1) 17 (9) 22 (10)

Left Ear II Present Study Abel et al [73]

(20W (2000) Mean (SD) Mean (SD)

91

To eliminate any variation from measurements on different individuals,

Lindeman et al 1771 studied a group of male subjects over a period of

6 years and measured their hearing thresholds ( 0 . 5 to 8 kHz

frequencies) every 3 years, at the ages of 17, 20, and 23 years, to

test whether hearing deteriorates during late adolescence. Their

results did not reveal any absolute hearing loss among male

adolescents, but a slight frequency-related deterioration at 1 and 2

kHz between the ages of 17 and 23 years. These changes, although

statistically signif icant , were not clinically relevant [71] . The

conclusion that there is no significant decline in hearing between

adolescence and early adulthood is also supported by Burén et al [78]

and Sakamoto et al 1791. The Sakamoto study [79] did note, however, an

increase in thresholds in their 30-39 year old group.

5.2 S~eech understandine in noise

The major handicap that derives from a hearing loss is a communication

def icit [3,4,46,80,66] . Thus, tests of speech understanding in noise provide an appropriate tool for assessing the severity of a hearing

loss .

Most children and adults recognize the ambiguous, sometimes even

distorted, acoustic cues provided in everyday conversation with

rernarkable ease [3]. While therc are multiple cues for recognizing

speech sounds, our knowledge of the language is essential. Therefore,

speech recognition depends partially on the acoustic signal and

partially on the listener's language experience. Presentation in noise

makes speech discrimination more difficult. This effect is even more

pronounced in hearing-impaired listeners [66,73,81].

The present study used the FAAF test presented at a listening level of

75 dB SPL presented in quiet and in speech-spectrum noise with a

signal-to-noise ratio of -5 dB. In other words, the speech-spectrum

noise was 5 dB greater in intensity than the speech. Abel and

coworkers [73] used the FAAF test presented at a listening level of 70

dB SPL in quiet and in speech-spectrum noise with a signal-to-noise

ratio of -10 dB. Both the present study and the Abel study [731

cornpared results of the FAAF test acxoss listening conditions (i.e.,

quiet and noise). In the present study of adolescents with normal

hearing, scores observed for speech discrimination in quiet and in

noise were relatively high, as were those of the Abel study [73]. In

the present study, the effect of speech-spectrum noise was a 20%

decline in the total consonant recognition score. Similarly, the

effect of speech-spectrum noise in the group of young adult subjects

(20-39 years) with normal hearing frorn the Abel study [73] showed a

20% decline in the total consonant discrimination score. In the

present study, mean consonant discrimination scores showed a 28%

decline for final consonant discrimination in noise and a 21% decline

for initial consonant discrimination in noise. Similarly, in the Abel

study [73] , mean consonant discrimination scores showed a 25% decline

for final consonant discrimination in noise and a 14% decline for

initial consonant discrimination in noise. Although the present study

showed poorer initial consonant discrimination (by 6%) than the Abel

study [73], the difference is not large enough to suspect hearing

impairment in subjects from the present study. This difference may be

93

attributable to attention deficits in the younger teenage subjects in

the present study compared to the older (20 to 39 year old) group in

the Abel study [731 .

5.3 Potential Sources of Hearine Loss in Teenagers and Young Adults

As many previous studies [ 4 , 5 , 6 , 4 7 , 4 9 , 5 0 ] have pointed out, noise

exposure can be considered a major factor influencing the hearing of

adolescents and young adults.

5.3.1 In utero and earlv childhood noise exDosUres

The high correlation found between mothers reporting noise at work and

hearing thresholds may be related to stress brought on by the

annoyance of the reported noise sources rather than the physical

characteristics of the noise sources themselves (e-g., intensity,

frequency) . There were only three subjects considered potentially at

risk for fatal NIHL and lack of information on their mother's

particular workplace made it difficult to ascertain true exposures.

However, the types of noise reported by the mothers were consistent

with known noisy industry (e.g., textiles).

It remains difficult to gauge the effects of occupational noise on the

fatus, especially since al1 three subjects in this study also reported

other sources of noise exposure (e .g. , al1 three subjects reported the

use of personal listening devices). The only subject who might be

considered at the limit of a slight average high-frequency hearing

94

loss (15 dB HL) had a mother that was occupationally exposed to noise

and to recreational fixearm use during pregnancy. Exposure to

occupational noise and gunfire are well docurnented as causing hearing

loss in adults. Perhaps such exposures may also have detrimental

effects on the fœtal auditory apparatus. However, there was not enough

data to explore this possibility.

5.3.2 Noisy teenage hobbies

Noise sources axe a potential hazard to hearing. However, the nature

and the types of sources that can cause noise-induced hearing loss are

still anibiguous. This is especially true with regards to leisure

noise, where the response may Vary in level and duration. In this

study, al1 subjects had thresholds that £el1 within "normal limits".

Thus, there appears to be no effect of noisy hobbies on hearing. This

outcome could be related to the age of the individuals studied. The

14-16 year olds may not be participating in the noisy leisure

activities they reported on a regular basis. There is no doubt that

more study is needed to elucidate whether noisy recreational

activities are related to the decline in hearing thresholds observed

in a number of studies [5,6] involving young adults in their late

teens and twenties.

5.3.3 Long-terrn effects of otitis media

The repeated-measures ANOVA in the present study found a statistically

significant effect of otitis media history on heaxing thresholds

95

whereby subjects that reported a history of otitis media had

consistently higher thresholds (1 to 3 dB higher) than those with no

history. This was true for both ears at al1 frequencies, with the

exception of the 4 kHz frequency in the right ear. In this case,

thresholds were 3 dB higher for the gxoup with no reported history of

otitis media. The greatest observed threshold difference was not large

in absolute sense (3 d ~ ) . Consequently the effect of otitis media

history is not considered to be clinically relevant [71].

5.4 Hearine Threshold Asvmmetw: The 'Ear' Effect

Numerous studies [82,83,84,85] have found asymmetries in hearing

thresholds in non-military populations. The left ear showed the

highest hearing thresholds in the high frequencies (above 2 kHz) but

had lower hearing thresholds than the right ear in the lower

frequencies (especially the 250 and 500 Hz frequencies). An

association had been found between noise exposure and left ear

thresholds in these studies.

In the present study, one-way repeated-measures ANOVA also revealed a

left-right asymmetry in hearing thresholds- Although the ear

differences were statistically significant, they were not clinically

significant [71] . The greatest ear difference was observed at 10 kHz,

where the left ear thresholds were 4.6 dB higher than the right ear

thresholds. Pirilà and coworkers [841 showed that between the aqes of

5 and 10 years, the left ear has better hearing thresholds than the

right ear for al1 audiometric frequencies in the standard range (i.e.

96

from 0 . 2 5 to 8 kHz) - In older subjects (15-50 years), however, there

was a left ear inferiority at the higher frequencies (most marked at

3-6 k H z ) . They examined whether this left ear inferiority, at high-

frequencies, is associated with noise damage or presbyacusis in a

random population divided into three age groups (5-10 years, 15-50

years, and over 50 years of age). They found that the left ear

inferiority at 4 kHz was present only in the 15-50 year old group and

not in the over 50 year old group. They then concluded that the

observed left ear inferiority at 4 lcHz must be attributable to noise

damage rather than presbyacusis. In retrospect, it should be expected

that with either intense noise exposure or age (and hence more noise

exposures of al1 kinds) one should observe a decline in hearing

predominantly in the left ear at the higher frequencies (since these

are the frequencies predominantly involved in NIHL) . On the other

hand, results by Merluzzi et al [SI showed statistically significant

effects of loud music on hearing thresholds for the right ear at al1

frequencies. Their only noted significant effects of loud music on

hearing thxesholds in the left ear were observed for the 500 Hz

frequency.

5.5 Limitations and Weaknesses of the Studv

5.5.1 Studvdesign

Initially, a cohort design was proposed to study the effects of in

utero occupational noise exposure on hearing in teenagers. Because of

the low response rate and small number of occupationally exposed

pregnant mothers, absolute hearing in adolescents relative to data

presented for similar age groups, older teenagers and young adults in

published studies was investigated.

Many other factors, besides the various sources of noise exposures,

are potential confounders. Therefore, a subtle effect of any of these

may well have been difficult or impossible to identify in this study.

Several common selection biases have been described in relation to

prospective, cohort studies [86]. For example, certain schools were

selected based on contact teachers who were familiar with the

laboratory where the study was conducted, subjects with hearing

difficulties in the farnily may have been more interested in

participating in the study than others. A gender bias was introduced

because the schools with the highest participation rate were private

schools with female-only enrolment.

The small sample size was the greatest limitation to the statistical

power and generalization of findings. In addition to this obvious

limiting factor, some questionnaire responses introduced data

collection biases. Given the ototoxicity of various drugs, subjects

were asked about any current medications they were taking before being

scheduled for testing. Any drugs taken in the past may have long term

effects. Consequently, they were noted in the detailed questionnaire.

However, due to the length of time and difficulty in recalling al1

previous medications adequately, a potential recall bias may have been

introduced. Numerous mothers could not remember the names of the

antibiotics their child took or the names of the drugs they took

during their pregnancy. Most of these drugs were over-the-counter

drugs, including NSAIDs like the salicylates. Their documented

ototoxic effects occur only at high doses and are reversible upon

discontinuation. The overall findings of this study are not likely to

have been influenced by the inclusion of these subjects. Nevertheless,

the effects of such drugs on the fœtal auditory apparatus remain

unknown. Additionally, the amount of time the mother's workplace was

noisy, as well as the various workplace noise sources, the sources of

leisure noise sources and the amount of time exposed to these leisure

noise sources are al1 potential recall biases. These questions

concerned the time when the mother was pregnant with the subject,

which was 14 to 16 years earlier, making it more difficult to recall

events accurately.

CHAPTER CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusions

No overall clinically significant hearing loss was observed in a group

of teenagers 14 to 16 years of age. No correlation was found between

hearing thresholds in the speech range (500 to 4000 Hz) and results

from the FAAF test in noise. Subjects with a history of otitis media

tended to have higher hearing thresholds, although none of the

findings were clinically significant. There was no evidence of an

effect of otitis media history on consonant discrimination in noise.

Recreational noise and drug exposures did not appear to be associated

with the measured outcomes. However, the exposure assessments were

based on crude questionnaire data, limiting the interpretation of

these findings, At individual frequencies, some subjects were found to

have hearing levels in excess of 16 dB HL and up to 26 dB HL, which

can be considered as 'slight' and 'mild* hearing loss [70]. Although

there were not enough subjects with in utero occupational noise

exposures , poorer-than-average FAAF test results (in noise) for these

3 subjects might suggest a harmful effect on hearing.

Although the present study was not successful in demonstrating a

clinically significant hearing loss in a group of otologically normal

teenagers, some studies [5,61 have found a significant decline in

hearing for young adults (18 to 25 years old) compared to standards

1 O0

and previously published studies. The question remains: Are we exposed

to more damaging sources and at younger ages than in the past?

6.2 Recommendations for Further Studv

The state of hearing in adolescents and young adults should be of

interest to physicians and occupational health care workers,

especially if hearing in young employees is already damaged when

starting a vocational career.

It would be interesting to re-test these same subjects 5 to 10 years

£rom now and collect information relative to potential sources of

hearing loss to see whethex there is a clinically significant hearing

loss from the age of 15 to 20 years.

Studies have shown that the left cochlea is more susceptible to noise

damage than the right cochlea. It would be interesting to see whether

the effects of occupational noise on the fœtus also produce hearing

loss predominantly in the left ear at the higher frequencies.

A prospective cohort study would allow more adequate identification

of in utero occupational noise. If periodic noise measurements could

be taken of pregnant mothers at their workplace, in utero occupational

noise exposures could be determined more accurately and without the

need for questionnaire-based estimations. However, questionnaires

would still be indispensable to eliminate the possible confounding of

non-occupational noise exposures from mothers' recreational activities

during pregnancy and sub j ect' s recreational activities f rom early

childhood to adolescence. It should also include information about

handedness to assess asymmetries in hearing threshold levels among

left and right-handed persons, more detailed information about otitis

media histories, and family history of hearing difficulties. Subject's

age range should be kept narrow and below 18 years. When comparing

other studies and standards to groups of younger teenage subjects,

signs of hearing loss that may possibly have arisen from recreational

noise do not seem to be present in the younger groups.

The creation of a nation-wide database for hearing would also help to

measure the development of hearing loss. It could include multiple

audiograms taken from the same individual, at 5 year intervals, from

early adolescence into adulthood. The lack of information about

hearing in teenagers makes it more difficult to assess possible risk

factors (other than occupational noise) to auditory health. Perhaps

the inclusion of a group of otologically normal 15-20 year olds should

form the basis of a standard, including thresholds in the extended

f requency range (8 to 20 kHz) .

APPENDLX 1

LETTER TO PARENTS AND STUDENTS

GAGE OCCUPATIONAL & ENVIRONMENTAL HEALTH UNIT Department of Public Health Sciences

Faculty of Medicine UN/VERS/TY OF TORONTO

223 College Street Toronto, ON, Canada

M5T 1 R4 Current Date,

Dear Grade 9/ 10 Student and Parents:

We are conducting a study to examine whether exposure to noise during pregnancy may cause a hearing impairnent in adolescent offspnng. With the agreement of the Toronto District School Board and your Principal (princival's name), we are approaching al1 grade 9 and 10 students at yow school to ask if you would be willing to participate in our study.

Participation in the study would first involve completing the enclosed screening questionnaire. We will select students, some whose mothers had industrial noise exposure during their pregnancy and others whose mothers did not have industrial noise exposure during pregnancy. These students would then be asked to visit the Hearing Research Laboratory at Mt. Sinai Hospital for one test session, after school, at a mutually agreeable time for hearing tests. These tests are completely non invasive and present no risk or h m . Students who complete this study will receive $15 for their time. The student's mother would also be asked to complete a more detailed questionnaire.

While we would be grateful for your help, your participation is voluntary. Your answers will be confidential and the study results will be reported in a manner that will not allow individuals to be identified. Participation in this study will not affect attendance in class or evaluation by the school. If you have any questions regarding the study, please feel fiee to contact either one of us. Please complete the questionnaire and return to your teacher sealed in the envelope provided within the next 10 days. Those who are selected will be contacted via phone by Ms-Valerie Phelan.

Thank you very much for your consideration.

Yours sincerely,

Andrea Sass-Kortsak, PhD Associate Professor & Co-Principal Investigator

Sharon M. Abel, PhD Pro fessor &

Co-Principal Investigator

APPENDIX II

SCREENING OUESTIONNAIRE

(Modified to fit thesis format)

GAGE OCCUPATIONAL & ENVIRONMENTAL HEALTH UNIT Department of Public Health Sciences

Faculty of Medicine UNIVERSITY OF TORONTO

223 College Street Toronto, ON, Canada

MST 1R4

OCCUPATIONAL NOISE EXPOSURE DURIP

SCREENING QUESTIONNAIRE (To be filled out by Mother)

Student's LAST NAME: FiRST NAME:

Date of Birth Year: Month: Day :

Mother's LAST NAME: FIRST NAME:

Address: Street: Apt:

City: Province: Postal Code:

Tele~hone: Day: Evening :

FOR LAB USE: DO NOT FLL

SUBJECT NUMBER /////

FOR LAB USE: DO NOT FILL

SubjectNumbed / / / /

Al. Were you working outside

O Yes

if yes P

the home

0 No

while pregnant with your child

If no skip to question B 1

(the subject)?

M. During which months of your pregnancy were you workùig: (check each that applies)

O 1 to 3 months O 4 to 6 months 7 to 9 months

Please describe your job and the employer you worked for during your pregnancy:

A3. Job title

A4. Job description

AS. What did your employer (company) do or make:

A6. How would you describe your immediate work environment, during that job?

Factory/Plant floor O Laboratory Vehicle Outside Warehouse floor Construction Site LI Restaurant/Hotel

17 OfficelClassroom/School OOther, please describe:

A7. Were you exposed to noise in your workplace? O Yes

If yes * Please describe the source and nature of the noise (e.g. Cornpressor machine, loud and intermittent 'thurnping' noise)

FOR CAB USE: DO NOT FILL

SubjectNumberl / / / !

BI. While pregnant with the above child did you engage in non work related activities where you were exposed to noise?

O Yes O No

If yes* B2 Which of the following sources of loud sound applied to you in your leisure activities (i.e. when you were not at work)?

Rock music/Concerts Cl Guns DiscolDance bars Snowmobiles Persona1 headphones Other: (please list) Motorcycles

O Power tools

B3. M a t is the approximate total amount of time (houdweek) you were exposed to al1 of the leisure activities that you indicated in the question above?

O Oto5hours O 6tolOhours O 1 1 to 20 hours O 21 to 30 hours a More than 30 hours

CI. Was your child bom prematurely?

O Yes

C2. Does your child have a history of :

Ear infections O Yes O No Ear surgery OYes O No Head trauma O Yes O No

FOR LAB USE: DO NOT FILL

Subject Number / / / / /

If you and your child are selected for inclusion in the study, would you be willing to:

a) to provide us with more detailed infoxmation related to the period during your pregnancy (Le. regarding noise exposures, therapeutic drug use, smoking and alcohol consurnption, family history of hearing loss)

O Yes O No

b) to allow your child to go to the Hearing Research Laboratory at Mt. Sinai Hospital to have hisher hearing acuity tested using procedures that are NOT invasive, harmful or stressful

O Yes O No

D2. Would you prefer more information (we will gladly discuss the study in more detail)?

O Yes O No

Please indicate the best day/time and the appropnate phone number for us to reach you:

Daytime Between the hours of:

Phone number:

Evening W Between the hours of:

Phone number:

THANK YOU VERY MUCH for taking the time to fil1 out this questionnaire.

Your participation is greatly appreciated.

APPENDIX III

DETAJLED OUESTIONNAIRE

(Modified to fit thesis format)

GAGE OCCUPATIONAL & ENVIRONMENTAL HEALTH UNIT Department of Public Health Sciences

Faculty of Medicine UNIVERSITY OF TORONTO

223 College Street Toronto, ON, Canada

M5T IR4

OCCUPATIONAL NOISE EXPOSURE DURING PREGNANCY

QUESTIONNAIRE

(To be filled out by Mother)

Name of Student:

Mothers name:

A. GENERAL INFORMATION

A 1 Year of Birth (mother) 19-

A2. How many children have you had? (including stillbirths and miscarriages) For each child, please indicate the sex and year of birth or whether miscarriage or stillbirth:

year of birth Child 1: Child 2: Child 3: Child 4: Child 5: Child 6:

Subject

A3. Are you aware of any difficulties that your child may have with respect to hisiher hearing?

O Yes O No

If yes please describe:

A4. Has your child ever had:

Ear infections O Yes Ear Surgery O Yes Bacterial Meningitis O Yes Mumps O Yes Measles O Yes Jaundice O Yes

AS. At birth, was your child full tenn: O Yes

If no QF how many weeks early:

What was the approximate birth weight of your child?

Cljlbs or Cllkg

Did your child spend time in a neonatal intensive care unit (NICU)?

O Yes O No

Please list al1 the medications, including antibiotics, your child has taken [since birth] (exciuding aspirin, tylenol, and common cold/cough medications):

Ag. Do any of the student's imrnediate relatives have a history of any problems with their ears or hearing?

Mother (you) O Yes O No Father O Yes O No Materna1 grandparents O Yes O No Patemal grandparents O Yes O No Sisters/brothers O Yes O No

If yes * please describe:

A1 0. During your pregnancy did you smoke cigarettes?

O Yes O No

If yes 0- approximately how many cigarettes per day did you smoke?

approximately 10 cigarettes per day (% pack) 0 approximately 20 cigarettes per day (one pack)

more than one pack per day

A l 1. During your pregnancy, did you drink alcoholic beverages?

O Yes O No

If yes approximately how much did you drink

less than 1 dnnk per week 0 1 drink per week

1 drink per day O more than 1 drink per day

A12. Durhg your pregnancy, did you take any medications/drugs (Le. over-the-counter dmgs, prescription drugs)?

O Yes O No

Ifyes what kinds, please describe:

A1 3. During your pregnancy did you have:

Rubella O Yes O No Herpes O Yes O No

O Don't know O Don't know

B. WORK HISTORY

BI. Were you working outside the home while pregnant with the above student?

O Yes

If yes * Please describe your job and detail as you can:

skip to question C 1

the employer you worked for in as much

B2. Job title

B3. Job description

B4. Narne of Employer: (we wiii not contact employers, but knowing the empIoyer will help us identiw workplace conditions of interes't to our study)

BS. What did your employer (company) do or make:

B6. How would you descnbe your imrnediate work environment?

FactoryPlant floor O Laboratory Vehicle Outside O Warehouse floor O Construction Site Restaurant/Hotel rn Office/classroom/school CIOther,please describe:

B7. Were you exposed to noise in your workplace? O Yes O No

I f y e s e B7.1 Wasyourworkareanoisy?

Very rarely (never) less than !4 of the time (seldom) about K of the time (sometimes) more than -Xi of the time (O ften)

0 Always

B7.2 On average, how loud was the noise in your opinion?

0 Not noisy Low/mild Medium/moderate Highlsevere Extremely high

B7.3 Did you Wear hearing protection at work?

Never less than !4 ofthe tirne

O about % of the time more than % of the time Always

B7.4 If so, what kind of protectors?

Ear Plugs O Ear Muffs

Plugs and muffs together

B7.5 Please describe the source and nature of the noise (e.g. Compressor machine, loud and intermittent 'thumping' noise)

B8. Where you exposed to solvents in your workplace, during your pregnanc y?

O Yes O No O Don't know

If yes * B8.1 Which solvents (please list all)?

88.2 How ofien were you exposed to these solvents ?

Daily O Weelûy

Monthly, or less

B8.3 To what level were you exposed?

Low/mild O Mediundmoderate

Highkevere Extremely high

01 Don't Know

B8.4 Did you Wear respiratory equipment?

O Never less than !4 of the t h e

Cl about '/z of the time O more than 34 of the time

Always

B8.5 I f so, what kind of protection?

O Dust Masks Organic Vapour cartridge respirator Other, Please describe :

C. NON-OCCUPATIONAL NOISE

C l . While pregnant with the above student did you engage in non work related (leisure) activities where you were exposed to noise?

O Yes O No If no * skip to question Dl

rf yes 9

C2. WIiile pregnant, which of the following sources of loud sound applied to you in your Ieisure activities (Le. when you were not at work)?

0 Rock music Cl Guns Disco/Dance bars Ci Snowmobiles/Jet skis

O Power tools 17 Other: (please list) O Motorcycles

Persona1 headphones

C3. What is the approximate total arnount of time (hours/week) you were exposed to al1 the leisure activities that you indicated in the question above?

O to 5 hours 6 t o 10hows 1 1 to 20 hours 21to30hours More than 30 hours

D. ABOUT YOUR CHILD

Dl. Does you child:

Play music in a band 0 Yes O No O Don't know Go to rock concerts O Yes O No O Don't know Wear stereo headphones O Yes O No O Don't know Have any noisy hobbies O Yes O No O Don't know

If yes * Please describe:

Thank you very much for your help

APPENDEX IV

CONSENT FORM

(actual fom on Mt. Sinai Hospital letterhead)

It has been explained to me that this study, conducted by Drs. Andrea Sass-Kortsak and Sharon Abel, is concemed with the effects of materna1 noise exposure during pregnancy on hearing in adolescent offspring. This study has the support of the Toronto District School Board.

Based on the screening questionnaire distributed at my school and completed by my mother, 1 have been invited to participate. 1 will be assigned to a group of students whose mothers either (1) were exposed to industrial noise during pregnancy, or (2) were not exposed to industrial noise.

As a participant, 1 will be asked to visit the Hearing Research Laboratory at Mt. Sinai Hospital for one session, lasting approximately 1 hour. First, my hearing will be tested in each ear at ten different sound frequencies. Then, my ability to understand words presented in quiet or against a moderately noisy background will be assessed* For both of these tests 1 will be seated in a sound proof booth and the sounds will be presented to me over earphones. The measurements do not constitute a medical evaluation of hearing; however, if 1 wish, a copy of the results will be sent to my family physician."

The procedures are in no way invasive, harmfbl or stressful. The study will follow the ethical standards for research of both the University of Toronto and the Toronto District School Board. If, for any reason, 1 am uncornfortable with the procedures, 1 may withdraw form the study at any tirne. If 1 complete the study, 1 will be paid the amount of $1 5 for my time. Participation in this study will not affect my attendance in class or rny evaluation by the school. Al1 my results will be held in strict confidence and will be reported only as part of group trends, without identimng me personally. If 1 have any concems or questions relating to the study, 1 may contact either Dr. Abel (4 16-597-3422 ext. 3928) or Dr. Sass-Kortsak (4 16-978-6239).

1 agree to participate in this study:

Name of S tudent/Subject Signature of Student/Subject Date

1 agree to allow my soddaughter to participate:

Name of Mother Signature of Mother Date

*If you would like the results of the tests to be forwarded to your family physician, please provide hif ier name and address:

APPENDYiC V

DATASHEETS

THRESHOLD TRACKING DATA SHEET

DATE:

PARAMETERS : Room: SEMI-REVERBERANT Mode: TDH -49P (Monaural) Stimulus type: PURE TONE Background: QUIET

PI: 150 ms WD: 50 ms Stimulus Duration: 250 ms Number of Frequencies: 9 Programmable Attenuation: 30 dB

EAR: Rinht FREQ (Hz)

-

Manual Track Att (dB) Att (dB)

- -

Total Thres ho ld An (dB) (dB SPL)

EAR: Lefi FREQ (Hz)

Manual Track Total Threshold Att (dB) Att (dB) An (dB) (dB SPL)

FREQ (Hz) 125 250 500 1000 2000 3000 4000 6000 8000 10000 EAR Dm!: R-L (dB) .-. - - - - - - - - -

- - -

COMMENTS:

FAAF DATA SHEET

NAME : ID: DATE:

PARAMETERS : Room: SEMI-REVERBERANT Presentation: TDH 4 9 P (BinauraI) Speech Level: 75 dB SPL Noise Level: 80 dB SPL Signal-to-Noise ratio ( S N ) : -5 dB

MONOPHONIC ROTEL: O dB Programmable Attenuation: O dB

BACKGROUND: QUIET

Speech Intensity: 75 dB SPL

Promammable Aît: O dB SPL

Att A: 29 dB SPL

FAAF List:

Raw Score %Correct

Total: 140

initial: 11 8

Final: 122

BACKGROUND: Speech Svectrum Noise FAAF List:

Raw Score %Correct

Speech htensitv: 75 dB SPL Total : 140

Programmable Att: O dB SPL

Att A: 23 dB SPL

Noise Intensity: 80 dB SPL

Programmable Att: O dB SPL

Initiai: 118

Final: /22

Att B: 25 dB SPL

SAMPLE FAAF TEST

D a t e : Condition: .------.---- ----- -.--

FAAF II: T e s t B: Practice

hold

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s tone

s tream

what

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scxeam

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cold

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man

dab

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ham

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some

boast

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rose

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van

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b a i l

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mas s

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tab

r i d s

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how

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FAAF II: Test B t Paqa 3

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REFERENCES

1 Berglund B., Lindvall T., (1995). Communitv Noise, VoIurne 2 ( l) , Center for Sensory Research, Stockholm.

2 Jarvelin M-R., Maki-Torkko E., S o m M.J., (1997). Effect of hearing impairment on educational outcomes and employment up to the age of 25 years in northern Finland , Brit J Audiol 3 1, 165-175.

3 Northem J.L., Downs M.P., (1991). Aearine in Children, 4" ed , Williams & Wilkins, Baltimore.

4 Niskar A.S., Kiesz;ik SM., Holmes A., Esteban E., Rubin C., Brody D.J., (1998). Prevalence of hearing loss among children 6-19 years of age: The 3rd national health and nutrition examination survey, JAMA 279 (14), 1071-1075.

5 Merluzzi F., Arpini A., Carnerino D., Barducci M., Marazzi P., (1997). La soglia uditiva in giovani Italiani di 1û-19 anni, Med Lav 88 (3), 183-195.

6 Smith P.A., Davis A., Ferguson M., Lutman M.E., (2000). The prevalence and type of social noise exposure in young adults in England, Noise & Health 6,4146.

7 ISO 389 (1991). Specification for standard reference zero for the calibration of pure tone air conduction audiometers, International Organization for Standardization, Geneva.

8 ISO 7029 (1984). Thresholds of hearing by air conduction as a function of age and sex for otologically normal persons, intemational Organization for Standardization, Geneva.

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