PHYSIOLOGY OF HEARING AND RELEVANT TESTS [Autosaved].pptx

Hearing

1. PHYSIOLOGY OF HEARING AND RELEVANT TESTS Done by VIGNESH E

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).

8. TRANSDUCTION Transduction is the conversion of mechanical energy to electrical energy . Round Window Reflex Organ of corti

9. Major steps of transduction

10. ELECTRIC POTENTIAL Endocochlear Potential Cochlear Microphonic (CM) Summating Potential (SP) Compound Action Potential

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. CLINICAL TESTS OF HEARING 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

18. RINNIE TEST

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.

20. WEBER TEST

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

25. AUDIOMETRIC TESTS Pure Tone Audiometry Speech Audiometry Bekesy Audiometry Impedance Audiometry

26. TWO ROOM AUDIOMETRY SETUP

27. SOURCES

28. THANK YOU