Audiometry

Dr. Vishal Sharma

Pure Tone Audiometer

Pure Tone Audiometry • 5 up, 10 down technique used with single

frequency tones to find hearing threshold.

• 2 correct responses out of 3 is acceptable.

• Air conduction measured for 1K, 2K, 4K, 8K,

500, 250 & 125 Hz via head phone.

• Bone conduction measured for 1K, 2K, 4K, 500

& 250 Hz via bone vibrator. Masking of other ear.

• Normal hearing for AC & BC is at 0 dB.

Symbols used in audiogram

Normal Audiogram

Pure Tone AverageCalculated by taking arithmetic mean of air conduction

thresholds at 500, 1000 & 2000 Hz (speech frequencies)

Classification of Deafness: Goodmann & Clark

P.T.A. (dB) Type P.T.A. (dB) Type

0 - 15 Normal 56 – 70 Moderate Severe

16 – 25 Minimal 71 – 91 Severe

26 – 40 Mild > 91 Profound

41 – 55 Moderate

Conductive deafness

Sensori-neural deafness

Mixed deafness

Diagnosis of type of deafnessType Air

ConductionBone

ConductionAir bone

gap

Conductive Worsened Normal Present

Sensori-neural

Worsened Worsened Absent

Mixed Worsened Worsened Present

Low frequency conductive HL

Otitis media with effusion

Carhart’s notch (otosclerosis)

High frequency SNHL

Presbyacusis, ototoxicity, acoustic neuroma

Low frequency SNHL (Meniere)

Deafness in Meniere’s disease

Acoustic dip (Noise deafness)

Uses of pure tone audiogram

1. To find type of hearing loss

2. To find degree of hearing loss

3. For prescription of hearing aid

4. Predict hearing improvement after ear surgery

5. To predict speech reception threshold

6. A record for future medico-legal reference

Speech Audiometry

Speech Reception Threshold (S.R.T.): Minimum

intensity at which 50% of spondee (disyllable with

equal stress) words are correctly identified.

S.R.T. is normally within 10 dB of Pure Tone Average.

Speech Discrimination Score (S.D.S.): Percentage

of phonetically balanced (single syllable) words

correctly identified at 40 dB above S.R.T.

Speech Audiometry

PB max Score: Maximum SDS at any intensity.

Uses of Speech Audiometry

• Differ b/w cochlear & retro-cochlear lesions.

• Volume of hearing aid fixed at PB max score

• In functional deafness: SRT > + 10 dB of pure

tone average.

Speech Audiogram

Speech DiscriminationHearing loss Speech understanding

0 – 25 dB No difficulty with faint speech

26 – 40 dB Difficulty with faint speech only

41 – 55 dB Difficulty with faint + normal speech

56 – 70 dB Difficulty even with loud speech

71 – 91 dB Only understands amplified speech

> 91 dB Can’t understand amplified speech

Special Audiological Tests

Tests for Recruitment

Recruitment is abnormal growth in perception

of sound intensity. Tests of recruitment are

done to diagnose a cochlear pathology.

Tests used are:

1. Short Increment Sensitivity Index (SISI) Test

2. Alternate Binaural Loudness Balance (ABLB) Test

S.I.S.I. Test (Jerger, 1959)• Continuous tone given 20 dB above

hearing threshold & sustained for 2 min.

• Every 5 sec, tone intensity increased by 1

db and 20 such blips are given.

• SISI score = % of blips heard.

• 70-100 % in cochlear deafness

• 0-20 % in conductive & nerve deafness

A.B.L.B. Test (Fowler, 1936)Pure tone is presented alternately to deaf &

normal ear. Intensity heard in normal ear is

adjusted to match with deaf ear. Test started 20

dB above threshold in normal ear & repeated with

10 dB raises till loudness is matched in both ears.

Initial difference is maintained, decreased &

increased in conductive, cochlear & retro-

cochlear lesions respectively.

Laddergram in A.B.L.B. test

Threshold Tone Decay Test

• Olsen & Noffsinger (1974)

• Detects abnormal auditory adaptation due to

nerve fatigue caused by a retro-cochlear lesion.

• Pure tone presented 20 dB above hearing

threshold, continuously for 1 min. If pt stops

hearing earlier, intensity ed by 5 dB & restart.

• Test continued till pt hears tone continuously

for 1 min or intensity increment (decay) > 25 dB

InterpretationTone Decay Pathology

dB Type

0-5 Absent Normal

10-15 Mild Cochlear

20-25 Moderate Cochlear

> 25 Severe Retro-Cochlear

Impedance Audiometry

Impedance Audiometer Probe

A = oscillator (220 Hz). B = air pump C = microphone to pick up reflected sound

Impedance Audiometry

1. Tympanometry

2. Acoustic reflex (Stapedial reflex)

Principles of Tympanometry

a. Less compliant T.M. reflects more sound.

b. Maximum compliance of T.M. denotes equal

pressure in E.A.C. & middle ear.

Tympanogram parametersAdult Child

Compliance 0.5 – 1.75 ml 0.5 – 1.75 ml

Middle ear pressure

+ 100 to - 100 Deca Pascal

+ 60 to - 100 Deca Pascal

External Auditory Canal

volume

1.0 – 3.0 ml 0.5 – 2.0 ml

Tympanogram Types (Jerger)

Types of TympanogramType Pressure Compliance Seen in

A Normal Normal Normal ME

As Normal Decreased Otosclerosis

Ad Normal Increased Ossicular discontinuity

B Nil (flat curve) Nil (flat curve) Fluid in ME, TM perforation

C Negative Normal ET obstruction

Type A

Type As

Type Ad

Type B (fluid in middle ear)

EAC volume = 1.8 ml

Type B (T.M. perforation, grommet)

EAC volume = 3.2 ml

Type B (E.A.C. obstruction)

EAC volume = 0.4 ml

Type C

Acoustic Reflex Loud sound > 70 dB above hearing threshold,

causes B/L contraction of stapedius muscles, detected by tympanometry as se in compliance.

Uses of Acoustic Reflex1. Objective hearing test in infants & malingerers

2. Presence of reflex at <60 dB above threshold is

seen in cochlear lesion due to recruitment

3. Reflex amplitude decay of > 50 % within 10 sec

is seen in retro-cochlear lesion

4. Absence of reflex seen in facial nerve lesion

proximal to stapedius nv & in severe deafness

5. I/L reflex present, C/L absent in brainstem

lesion

B/L reflexes present

Stapedial reflex absent

Acoustic Reflex Decay

Electro-cochleography

Measures auditory stimulus related cochlear

potentials by placing an electrode within external

auditory canal / on tympanic membrane / trans-

tympanic placement on round window.

3 major components:

a. Cochlear microphonics: from outer hair cells

b. Summating potential: from inner hair cells

c. Compound Action potential: from auditory nerve

Trans-tympanic electrode

Electro-cochleography findings in Meniere’s disease

• Summation potential : compound action

potential ratio > 30 %

• Widened waveform

• Distorted cochlear microphonics

SP – AP Waveform

Cochlear Microphonics

Normal

SP/AP > 30 %

Distorted CM

Otoacoustic Emission (Kemp echoes)

Sounds generated within normal cochlea due to

activities of outer hair cells.

Types: 1. Spontaneous: absent in > 25 dB HL

2. Evoked: transient; distortion product

Applications: Objective & non-invasive test for:

1. Hearing screening in neonates

2. Evaluation of non-organic hearing loss

Otoacoustic Emissions (OAE)

• Spontaneous OAE: Sounds emitted without stimulus

• Transient evoked OAE: Sounds emitted in response

to click stimulus of very short

duration

• Distortion product OAE: Sounds emitted in

response to 2 simultaneous tones of

different frequencies & intensities

• Sustained-frequency OAE: Sounds emitted in

response to a continuous tone

Normal Spontaneous OAE

Normal Transient evoked OAE

Normal Transient evoked OAE

Normal Distortion Product OAE

Early detection of N.I.H.L.

Early stage N.I.H.L.

Advanced stage N.I.H.L.

Malingering of N.I.H.L.

Auditory Evoked Potentials

Auditory Evoked Potentials

• Auditory Brainstem Response: 1.5-10 ms post

stimulus; originates in 8th cranial nerve (waves I & II)

up to lateral lemniscus & inferior colliculus (wave V)

• Middle Latency Response (MLR): 25-50 ms post

stimulus; arises in upper brainstem & auditory cortex

• Slow Cortical Response: 50-200 ms post stimulus;

originating in auditory cortex

Brainstem Evoked Response Audiometry (B.E.R.A.)

Auditory evoked neuro-electric potentials

recorded within 10 msec from scalp electrodes.

Applications: Objective test

1. Hearing threshold for uncooperative pt / malingerer

2. Hearing threshold in sleeping / sedated / comatose

3. Diagnosis of retro-cochlear pathology

4. Diagnosis of C.N.S. maturity in newborns

5. Intra-op monitoring of auditory function

Hearing test of comatose pt

Anatomy of B.E.R.A. waves

B.E.R.A. waves

Normal inter-wave latencies

Cortical Evoked Response Audiometry (CERA) or P1-N1-P2 response

• good frequency specificity over speech

frequency range (500-3000 Hz)

• recorded from higher auditory level than BERA,

so less subject to organic neurologic disorders

• CERA must be done to evaluate accurate

hearing threshold in pt with flat audiogram &

hearing threshold of > 25 dB at 500 Hz

Multiple Auditory Steady-state Evoked Response audiometry

• Are responses to rapid stimuli where brain response to

one stimulus overlaps with responses to other stimuli

• Slow rate responses (<20 Hz) arise in cortex & faster

rate responses (>70 Hz) originate in brainstem 

• Gives rapid, frequency specific & objective hearing

assessment by giving 4 continuous tones to each ear

Multiple Auditory Steady-state Evoked Response audiometry

Audio Test Cochlear Retro-cochlear

Speech Audiometry

S.D.S. = 60-80 % < 40 %, Roll over phenomenon

S.I.S.I. Positive (> 70 %) Negative

A.B.L.B. laddergram

Converging Diverging

Tone decay Negative (< 25dB) Positive (> 25dB)

Stapedial reflex Reflex at < 60 db SL; Decay absent

Reflex at > 70 db SL; Decay present

B.E.R.A. (Wave V latency)

< 4.2 msec > 4.2 msec

Thank You