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.
Dr. Vishal Sharma
Calculated by taking arithmetic mean of air conduction
thresholds at 500, 1000 & 2000 Hz (speech frequencies)
Otitis media with effusion
Presbyacusis, ototoxicity, acoustic neuroma
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 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.
PB max Score:Maximum SDS at any intensity.
Uses of Speech Audiometry
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
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.
for 1 min or intensity increment (decay) > 25 dB
A = oscillator (220 Hz). B = air pump C = microphone to pick up reflected sound
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.
EAC volume = 1.8 ml
EAC volume = 3.2 ml
EAC volume = 0.4 ml
Loud sound > 70 dB above hearing threshold, causes B/L contraction of stapedius muscles, detected by tympanometry as se in compliance.
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
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
SP/AP > 30 %
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:
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