Audiometry - The Medical Post

Audiometry - The Medical Post

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 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 Type Air

Bone Conduction Conduction Air bone gap Conductive

Worsened Normal Present Sensorineural

Worsened Worsened Absent Mixed

Worsened Worsened Present Low frequency conductive HL

Otitis media with effusion Carharts notch (otosclerosis) High frequency SNHL Presbyacusis, ototoxicity, acoustic neuroma

Low frequency SNHL (Meniere) Deafness in Menieres 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 Cant 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 & retrocochlear 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 Interpretation Tone Decay

Pathology dB Type 0-5

Absent Normal 10-15 Mild

Cochlear 20-25 Moderate Cochlear

Severe Retro-Cochlear > 25 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 0.5 1.75 ml

Middle ear pressure + 100 to - 100 Deca Pascal + 60 to - 100 Deca Pascal

1.0 3.0 ml 0.5 2.0 ml External Auditory Canal volume

Tympanogram Types (Jerger) Types of Tympanogram Type 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 Negative

Normal ET obstruction C 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 / transtympanic 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 Menieres 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: 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

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