Presentation on theme: "Audiometry Dr. Vishal Sharma. Pure Tone Audiometer."— Presentation transcript:
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
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) TypeP.T.A. (dB) Type Normal56 – 70Moderate Severe 16 – 25Minimal71 – 91Severe 26 – 40Mild> 91Profound 41 – 55Moderate
Diagnosis of type of deafness TypeAir Conduction Bone Conduction Air bone gap ConductiveWorsenedNormalPresent Sensori- neural Worsened Absent MixedWorsened 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 Discrimination Hearing lossSpeech understanding 0 – 25 dBNo difficulty with faint speech 26 – 40 dBDifficulty with faint speech only 41 – 55 dBDifficulty with faint + normal speech 56 – 70 dBDifficulty even with loud speech 71 – 91 dBOnly understands amplified speech > 91 dBCan’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 % 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 DecayPathology dBType 0-5AbsentNormal 10-15MildCochlear 20-25ModerateCochlear > 25SevereRetro-Cochlear
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 AdultChild Compliance0.5 – 1.75 ml Middle ear pressure to Deca Pascal + 60 to Deca Pascal External Auditory Canal volume 1.0 – 3.0 ml0.5 – 2.0 ml
Tympanogram Types (Jerger)
Types of Tympanogram TypePressureCompliance Seen in A Normal Normal ME As NormalDecreasedOtosclerosis Ad NormalIncreasedOssicular discontinuity B Nil (flat curve) Fluid in ME, TM perforation C NegativeNormalET obstruction
Type A s
Type A d
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
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
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 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 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 cortex Slow Cortical Response: 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
Normal inter-wave latencies
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 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 ( 70 Hz) originate in brainstem Gives rapid, frequency specific & objective hearing assessment by giving 4 continuous tones to each ear