3 Pure Tone Audiometry5 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.
20 Uses of pure tone audiogram 1. To find type of hearing loss2. To find degree of hearing loss3. For prescription of hearing aid4. Predict hearing improvement after ear surgery5. To predict speech reception threshold6. A record for future medico-legal reference
21 Speech AudiometrySpeech 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.
22 Speech Audiometry PB max Score: Maximum SDS at any intensity. Uses of Speech AudiometryDiffer b/w cochlear & retro-cochlear lesions.Volume of hearing aid fixed at PB max scoreIn functional deafness: SRT > + 10 dB of pure tone average.
26 Tests for Recruitment Recruitment is abnormal growth in perception of sound intensity. Tests of recruitment aredone to diagnose a cochlear pathology.Tests used are:1. Short Increment Sensitivity Index (SISI) Test2. Alternate Binaural Loudness Balance (ABLB) Test
27 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.% in cochlear deafness0-20 % in conductive & nerve deafness
28 A.B.L.B. Test (Fowler, 1936)Pure tone is presented alternately to deaf &normal ear. Intensity heard in normal ear isadjusted to match with deaf ear. Test started 20dB above threshold in normal ear & repeated with10 dB raises till loudness is matched in both ears.Initial difference is maintained, decreased &increased in conductive, cochlear & retro-cochlear lesions respectively.
30 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 continuouslyfor 1 min or intensity increment (decay) > 25 dB
31 Interpretation Tone Decay Pathology dB Type 0-5 Absent Normal 10-15 MildCochlear20-25Moderate> 25SevereRetro-Cochlear
33 Impedance Audiometer Probe A = oscillator (220 Hz). B = air pump C = microphone to pick up reflected sound
34 Impedance Audiometry 1. Tympanometry 2. Acoustic reflex (Stapedial reflex)Principles of Tympanometrya. Less compliant T.M. reflects more sound.b. Maximum compliance of T.M. denotes equal pressure in E.A.C. & middle ear.
35 Tympanogram parameters AdultChildCompliance0.5 – 1.75 mlMiddle ear pressure+ 100 to Deca Pascal+ 60 to Deca PascalExternalAuditory Canal volume1.0 – 3.0 ml0.5 – 2.0 ml
37 Types of Tympanogram Seen in Type Pressure Compliance A As Ad B C NormalNormal MEAsDecreasedOtosclerosisAdIncreasedOssicular discontinuityBNil (flat curve)Fluid in ME, TM perforationCNegativeET obstruction
45 Acoustic ReflexLoud sound > 70 dB above hearing threshold, causes B/L contraction of stapedius muscles, detected by tympanometry as se in compliance.
46 Uses of Acoustic Reflex 1. Objective hearing test in infants & malingerers2. Presence of reflex at <60 dB above threshold is seen in cochlear lesion due to recruitment3. Reflex amplitude decay of > 50 % within 10 sec is seen in retro-cochlear lesion4. Absence of reflex seen in facial nerve lesionproximal to stapedius nv & in severe deafness5. I/L reflex present, C/L absent in brainstem lesion
50 Electro-cochleography Measures auditory stimulus related cochlearpotentials by placing an electrode within externalauditory canal / on tympanic membrane / trans-tympanic placement on round window.3 major components:a. Cochlear microphonics: from outer hair cellsb. Summating potential: from inner hair cellsc. Compound Action potential: from auditory nerve
54 Cochlear Microphonics SP/AP > 30 %NormalDistorted CM
55 Otoacoustic Emission (Kemp echoes) Sounds generated within normal cochlea due toactivities of outer hair cells.Types: 1. Spontaneous: absent in > 25 dB HL2. Evoked: transient; distortion productApplications: Objective & non-invasive test for:Hearing screening in neonatesEvaluation of non-organic hearing loss
56 Otoacoustic Emissions (OAE) Spontaneous OAE: Sounds emitted without stimulusTransient evoked OAE: Sounds emitted in response to click stimulus of very short durationDistortion product OAE: Sounds emitted in response to 2 simultaneous tones of different frequencies & intensitiesSustained-frequency OAE: Sounds emitted in response to a continuous tone
66 Auditory Evoked Potentials Auditory Brainstem Response: ms post stimulus; originates in 8th cranial nerve (waves I & II) up to lateral lemniscus & inferior colliculus (wave V)Middle Latency Response (MLR): ms post stimulus; arises in upper brainstem & auditory cortexSlow Cortical Response: ms post stimulus; originating in auditory cortex
67 Brainstem Evoked Response Audiometry (B.E.R.A.) Auditory evoked neuro-electric potentialsrecorded within 10 msec from scalp electrodes.Applications: Objective test1. Hearing threshold for uncooperative pt / malingerer2. Hearing threshold in sleeping / sedated / comatose3. Diagnosis of retro-cochlear pathology4. Diagnosis of C.N.S. maturity in newborns5. Intra-op monitoring of auditory function
73 Cortical Evoked Response Audiometry (CERA) or P1-N1-P2 response good frequency specificity over speech frequency range ( Hz)recorded from higher auditory level than BERA, so less subject to organic neurologic disordersCERA must be done to evaluate accurate hearing threshold in pt with flat audiogram & hearing threshold of > 25 dB at 500 Hz
74 Multiple Auditory Steady-state Evoked Response audiometry Are responses to rapid stimuli where brain response to one stimulus overlaps with responses to other stimuliSlow 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