2. HOW IS SOUND WAVES
PRODUCED?????
Any vibrating object causes waves of compression and rarefaction is capable
of producing sound
Sound travels faster in liquids and solids than in air
When sound waves move from air to liquid 99 percent of waves get reflected due to
impedance offered by liquid
3. Physiology of
hearing
Pinna External auditory canal Tympanic membrane
Stapes footplate Pressure changes in labyrinth fluid
Movement of basilar membrane Stimulates hair cells of
organ of corti IHC of cochlea acts as transducers
4. CONDUCTION OF SOUND
PINNA
Pinna serves following functions because of its shape and location. It increases sound pressure
by 6 dB.
Collection
Localization
Concentration
External Auditory Canal
External Auditory Canal Along with pinna it can increase sound pressure at the tympanic
membrane by 15–22 db.
5. Impedance Matching
Mechanism
Middle ear converts sound of greater amplitude, but lesser force, to that of lesser amplitude and
greater force. This function of the middle ear is called impedance matching.
Hydraulic Action of Tympanic Membrane
Curved Membrane Effect
Lever Action of the Ossicles
6. Phase Differential
Between Oval and Round
Window
Acoustic Separation of Two Windows:
The sound should not reach both oval and round windows simultaneously.
This acoustic separation of two windows is provided by the tympanic membrane and a cushion of air in
the middle ear around the round window.
Aeration: Patent eustachian tube provides aeration to the middle ear.
7. Natural Resonance of
External and Middle Ear
Natural resonances of the external and middle ear allow certain frequencies of
sound to pass more easily to the inner ear.
The greatest sensitivity of the sound transmission is between 500 and 3000 Hz
(speech frequencies).
11. ASSESSMENT OF
HEARING
Hearing tests are done to assess hearing loss. It is of three types:
Conductive Hearing Loss.
Sensorineural (SN) Hearing Loss.
Mixed Hearing Loss
12. Hearing of an individual can be tested by clinical and audiometric tests.
A.CLINICAL TESTS OF HEARING
1. Finger friction test
2. Watch test
3. Speech tests
4. Tuning fork tests
13. Finger Friction Test
It is a rough but quick method of screening and consists of rubbing or
snapping the thumb and a finger close to patient’s ear.
14. Watch Test
Clicking watch is brought close to the ear and the distance at which it is
heard is measured. It had been popular as a screening test before the
audiometric era but is practically obsolete now. Clicking watches are also
obsolete
15. Speech (Voice) Tests
A person hears conversational voice at 12 m and whisper at 6 m
The patient stands with his test ear towards the examiner at a distance of 6m.
The examiner uses words or numbers with letters and gradually walks towards the patient.
DISADVANTAGE: Speech tests is lack of standardization in intensity and pitch of voice used for
testing and the ambient noise of the testing place.
16. TUNING FORK TESTS
These tests are performed with tuning forks of different frequencies such as 128, 256, 512, 1024,
2048 and 4096 Hz.
Tuning fork of 512 Hz is ideal.
A tuning fork is activated by striking it gently against the examiner’s elbow, heel of hand or the
rubber heel of the shoe.
17. RINNIE TEST
A vibrating tuning fork is placed on the patient’s mastoid and when he stops
hearing, it is brought beside the meatus.
Rinne test is called positive when AC is longer or louder than BC.
Eg: Seen patients having in sensorineural deafness
A negative Rinne (BC > AC) is seen in conductive deafness
19. WEBER TEST
In this test, a vibrating tuning fork is placed in the middle of the forehead or the
vertex and the patient is asked in which ear the sound is heard.
Normally, it is heard equally in both ears.
It is lateralized to the worse ear in conductive deafness and to the better ear in
sensorineural deafness.
21. Absolute Bone
Conduction (ABC) Test
Bone conduction is a measure of cochlear function. In ABC test, patient’s bone
conduction is compared with that of the examiner.
External auditory meatus of both the patient and examiner should be occluded to
prevent ambient noise.
In conductive deafness, the patient and the examiner hear the fork for the same
duration of time.
In sensorineural deafness, the patient hears the fork for a shorter duration.
22. SCHWABACH TEST
Here again Bone conduction of patient is compared with that of the normal
hearing person (examiner) but meatus is not occluded.
It has the same significance as absolute bone conduction test.
Schwabach is reduced in sensorineural deafness and lengthened in conductive
deafness
23. BING TEST
A vibrating tuning fork is placed on the mastoid while the examiner alternately
closes and opens the ear canal by pressing on the tragus inwards.
A normal person or one with sensorineural hearing loss hears louder when ear
canal is occluded and softer when the canal is open (Bing positive).
A patient with conductive hearing loss will appreciate no change (Bing negative)
24. GELLE TEST
Gelle’s test is performed by placing a vibrating fork on the mastoid while changes in air
pressure in the ear canal are brought about by Siegel’s speculum.
When air pressure is increased in the ear canal, causes immobility of basilar membrane
and decreased hearing when ossicular chain is fixed.
Gelle’s test is positive in normal persons and in those with sensorineural hearing loss.
It is negative when ossicular chain is fixed or disconnected.
It was a popular test to find out stapes fixation in otosclerosis
