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 Average Calculated 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 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 deafness Air Conduction Bone Conduction Air bone gap Conductive Worsened Normal Present Sensori-neural Absent Mixed

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 Discrimination Hearing 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

Interpretation Tone Decay Pathology dB Type 0-5 Absent Normal 10-15 Mild Cochlear 20-25 Moderate > 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 parameters Adult Child Compliance 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 Tympanogram Seen in Type Pressure Compliance A As Ad B C Normal Normal ME As Decreased Otosclerosis Ad Increased Ossicular discontinuity B Nil (flat curve) Fluid in ME, TM perforation C Negative 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 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

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 SP/AP > 30 % Normal 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: Hearing screening in neonates 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

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