noise induced hearing loss ika

8/13/2019 Noise Induced Hearing Loss IKA

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IKA YULIARTANTI

BAGIAN ILMU KESEHATAN THT-KL

FAKULTAS KEDOKTERAN UNPAD

BANDUNG


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INTRODUCTION

Sound effects organism as a whole, good and bad Excessive sound is one of the most common cause of hearing

loss in the world from military, industrial, and recreationalsources

Noise is define interms of its duration , frequency spectrum ( Hz), intensity inmeasured sound pressure level ( SPL) and expressed in decibels (dB)

It may be continuous, intermittent, impulsive or explosive,steady-state or fluctuant

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EFFECTS ON SOUND STIMULATION

ADAPTATION/PRE-STIMULATORY FATIGUE

Immediately phenomenon which occurs when a sound is presentedto the ear somewhat elevating the threshold

Greatest adaptation : 80dBSPL (fatiguing sounds)

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TEMPORARY THRESHOLD SHIFTPOST-STIMUL ATORY FATIGUE

Degree of TTS increases progressively with stimulusduration and intensity

A balance not being achieved until abnormal soundintensities are applied

The higher frequency >> TTS TTS recovers within 16 hours TTS greater than 40dB pathological associated with

residual PTS

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NOISE-INDUCED PERMANENT THRESHOLD SHIFT

Irreversible elevation of auditory threshold produced bynoise exposure, associated with permanent pathologicalchanges in the cochlea

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Risk of hearing loss and injury to the ear increaseswith :

1. Noise level2. Duration3. Number of exposures

4. Susceptibility of the individual

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CLASSIFICATION

1. Noise-induced temporary threshold shift

2. Noise-induced permanent threshold shift

3. Acute acoustic trauma

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Noise-induced

Temporary Threshold Shift

High frequency threshold shift

Steep isolated audiometric dipthe acoustic nocth 3kHz, 4kHz, 6kHz

Early stage : temporary thereshold shiftHearing usually return to the normal level if there noise

rest period


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Noise-induced Permanent Threshold Shift

Most encountered hearing loss caused by noise Hearing loss at 4kHz progress rapidly at first With 100dB daily 8-hour exposure Decrease 10-20dB within 1-2 years At lower frequency the loss is least severe & grows

more slowly


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A typical 4-KHz notch found after exposure to noise

Adapted from Scott- Browns, 6th Edition 1997.


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MECHANISM

1. NIHL involves the organ of Corti (the hair cells)

2. The outer hair cells are much more susceptible

to damageStereocilia

Less stiff Poorly responds to

the stimulation

Recovery normal mechanical

Properties and function

TTSTemporaryTresholdShift


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3. Increasing intensity and duration of exposure sufficientto cause NIPTS

MECHANISM

Fusion of adjacentstereocilia in outerhair cell

Loss of stereocilia

Noise Exposure

Hair cellDeath

Replaced by scar

Damage of inner hair cell

& supporting cell in organ of Corti Severe inner hair cell loss Secondary neural degeneration in

auditory nerve& brainstem auditory nuclei

NIPTSNoise InducedPermanentThreshold Shift


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Stereocilial damage associated with TTS,PTS. In the former, a shortening of thesupracuticular rootlet is the mostobvious anatomical change.

In PTS, rootlet fracture is ussualy evident

Schematic diagram of outer hair cell showingvarious organelles.

Adapted from Scott- Browns , 6th Edition

1997.


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Acoustic Trauma

Is the hearing loss produced by acute noise exposure.

History and physical finding

Onset: related to a single incident or to a brief episode exposure to an intense noise with or without

direct trauma to the head or ear. If examined within a few days after onset there

maybe otoscopic evidence of vascular congestion or

in the tympanic membrane.


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Pathophysiology Noise swelling or twisting of the outer hair

cells and pyknosis of their nuclei completeabsence of organon corti and rupture ofreissner membrane


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Audiologic findings Mild sensorineural hearing loss at 4,000Hz to majorlosses at all frequencies above 500Hz.

Some instances total hearing loss (anacusis)

Spontaneous nystagmus maybe present


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Diagnosis and Management

DD/ sudden hearing loss E/ of sudden hearing loss should kept in mind

If accompanied by obvious damage to the TM,

appropriate management of that injury is undertaken Total anacusis

Following acoustic trauma, the patient should strictly avoidnoise exposure while the hearing status is monitored byserial audiograms


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Interactions

A g i n g A middle-aged, noise-exposed worker with elevated HTLsmay be considered to have at least two components to hisor her hearing loss: NIPTS and aging.

Ward suggested that in addition to NIPTS we need toconsider three other factors:presbycus i s nosoacus i s s oc ioacus i s


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Vibration

Iki and co-workers vibration and noise may causegreater hearing loss than noise alone. Because manyindustrial environments combine these two factors, thisinteraction could be important.


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Drugs and Chemicals

Combining a noise exposure and an aminoglycoside drug cause hearing loss.

The ototoxic drug most likely to be combined with

industrial noise exposure is aspir in , but this causes areversible hearing loss.

Carbon monoxide (CO) and toluene sensorineuralhearing loss


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Men often display more hearing loss in noisyoccupations than do women, but this may be due to

different nonoccupational exposures (especiallyshooting) between the genders.

Susceptibility


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Factors possibly increasingsusceptibility to NIHL

Blue eyes,light skin Genetic predispotition Diatebes Cochlear hydrops Iron deficiency Vit. A deficiency

Aminoglycoside therapy

Cisplastinum therapy Older age Arteriosclerosis Smoking Atherogenic diet prematurity


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EVALUATION

Damage Risk Cri teria

Levels below about 80 dBA pose negligible risk to humanhearing over a working lifetime. Above 85 dBA, risk grows

rapidly for the high frequencies and more slowly for the lowfrequencies.


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Nonocc up at ion al Exposu res

The most important cause is gunfire. The impulses fromrifles and shotguns can range up to 170 dB at theshooters ear. The left ear of a right -handed shooter is at

greater risk because the right ear is somewhat protectedby the head shadow.


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Diagnosis of Noise-Induced Hearing Loss

A history of occupational or nonoccupational noiseexposure of hazardous intensity and duration should besought.

Sound-level measurements from the workplace, if

available, are most helpful.

Other etiologies of sensorineural hearing loss (heredity,ototoxicity, head injury, and so on) are primarily excludedby history.


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Physical examination external ear and middle eardisorders and occasionally may detect cranial nerve orbalance abnormalities that suggest an acoustic neuroma

The pure-tone audiogram in early cases usually shows anotch at 3, 4, or 6 kHz); loss becomes more severe andas aging changes are added to NIPTS.


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A series of audiograms

Laboratory and imaging tests indicated to rule out otherdisorders (acoustic neuroma)


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Criteria for diagnosis of occupational noise-inducedhearing loss

The principal characteristics of occupational noise-induced hearing loss are as follows:

1. It is always sensorineural affecting the hair cells in theinner ear.

2. It is almost always bilateral .3. It almost never produces a profound hearing loss.4. Once the exposure to noise is discontinued, there is

no significant further progression of hearing loss as a

result of the noise exposure.5. Previous noise-induced hearing loss does not

make the ear more sensitive to future noise exposure.


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6. The earliest damage to the inner ears reflects a loss at3,000, 4,000, and 6,000 Hz. The greatest loss usuallyoccurs at 4000 Hz.

7. Given stable exposure conditions, losses at 3,000, 4,000,and 6,000 Hz will usually reach a maximal level in about

10 to 15 years.

8. Continuous noise exposure over the years is moredamaging than interrupted exposure to noise, which

permits the ear to have a rest period.

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Handicap and Compensation.

The typical patient with a handicapping degreeof NIHL or presbycusis can hear speechwithout difficulty because of the low-frequency

power in vowel sounds but has difficultydiscriminating among consonants


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ManagementHearing Conservation OSHA)

SOUND LEVEL (dBA) DURATION OF EXPOSURE

90 895 4100 2105 1110 0,5115 0,25

Adapted from : R.F. Canalis and P.R. Lambert, The Ear: AcousticTrauma and Noise induced Hearing Loss.,2000


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The maximum permissible exposure (without hearingprotection) under OSHA regulations is 90 dBA

The essential components of an HCP are as follows: Noise measurements Engineering or administrative controls to reduce exposure Periodic audiometry with follow-up and referral Use of personal hearing protection devices (HPDs) Education, motivation, and counseling

MANAGEMENT


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The most important factors in choosing an HPD areproper fit and acceptance by the worker.

Counseling and motivation are crucial.

Hearing protectors

MANAGEMENT


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Clinical Management

Many physicians have advocated treatments,usually based on vasodilatation or hemorrheologiceffects, for acute acoustic trauma.

Hearing aids are helpful when hearing loss becomeshandicapping, but of course they do not restorenormal hearing.


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Noise-induced permanent threshold shift grows rapidly inthe high frequencies (3 to 6 kHz) and then deceleratesafter about 10 years.

Within the organ of Corti, the outer hair cells are mostsusceptible to noise-induced damage.

The most important nonoccupational cause of noise-induced hearing loss is gunfire.

HIGHLIGHTS


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Diagnosis of noise-induced hearing loss shouldnot be made on the basis of audiometric contouralone, but must include a careful history of

occupational and nonoccupational noiseexposure.

HIGHLIGHTS


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noise induced hearing loss ika

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