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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.

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audiometry

Audiometry

Dr. Vishal Sharma

pure tone audiometry
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.
pure tone average
Pure Tone Average

Calculated by taking arithmetic mean of air conduction

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

low frequency conductive hl
Low frequency conductive HL

Otitis media with effusion

high frequency snhl
High frequency SNHL

Presbyacusis, ototoxicity, acoustic neuroma

uses of pure tone audiogram
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 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.):Percentageof phonetically balanced (single syllable) words correctly identified at 40 dB above S.R.T.

speech audiometry22
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.
tests for recruitment
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
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
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.

threshold tone decay 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

impedance audiometer probe
Impedance Audiometer Probe

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

impedance audiometry34
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.

type b fluid in middle ear
Type B (fluid in middle ear)

EAC volume = 1.8 ml

type b e a c obstruction
Type B (E.A.C. obstruction)

EAC volume = 0.4 ml

acoustic reflex
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 reflex
Uses of Acoustic Reflex

1. 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

electro cochleography
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

electro cochleography findings in meniere s disease
Electro-cochleography findings in Meniere’s disease
  • Summation potential : compound action potential ratio > 30 %
  • Widened waveform
  • Distorted cochlear microphonics
cochlear microphonics
Cochlear Microphonics

SP/AP > 30 %

Normal

Distorted CM

otoacoustic emission kemp echoes
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:

  • Hearing screening in neonates
  • Evaluation of non-organic hearing loss
otoacoustic emissions oae
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
auditory evoked potentials66
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
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

cortical evoked response audiometry cera or p1 n1 p2 response
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
m ultiple a uditory st eady state e voked r esponse audiometry
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