1. HEARING- 3

2. LEARNING OBJECTIVES LEARNING OBJECTIVES Discuss the principles used in performing tests of hearing Discuss the principles used in performing tests of hearing An introduction to audiometry An introduction to audiometry Clinical significance of Otoacoustic emissions Clinical significance of Otoacoustic emissions Give an introduction to brain stem auditory evoked potentials Give an introduction to brain stem auditory evoked potentials

3. LEARNING OUTCOMES LEARNING OUTCOMES 28-30.10. Briefly explain the principle 28-30.10. Briefly explain the principle involved in tests of hearing in involved in tests of hearing in assessing defects of hearing assessing defects of hearing

4. Conduction of sound waves Air conduction Air conduction Bone conduction Bone conduction APPLIED AUDITORY PHYSIOLOGY

5. Deafness Types: Types: Conductive deafness Conductive deafness Sensorineural/perceptive deafness Sensorineural/perceptive deafness

6. CONDUCTIVE DEAFNESS Caused by… Caused by… Plugging of external auditory canal with excess wax or foreign bodies Plugging of external auditory canal with excess wax or foreign bodies Rupture of tympanic membrane, thickening of tympanic membrane Rupture of tympanic membrane, thickening of tympanic membrane Middle ear infections like Otitis media, Middle ear infections like Otitis media, Otosclerosis – Fixation of foot plate of stapes to oval window Otosclerosis – Fixation of foot plate of stapes to oval window

7. SENSORINEURAL DEAFNESS May be due to… May be due to… Injury to hair cell (due to extereme loud sounds) Injury to hair cell (due to extereme loud sounds) Aminoglycoside antibiotics like streptomicin, gentamicin blocking the mechanosensitive channels in stercocilia or degeneration of hair cells Aminoglycoside antibiotics like streptomicin, gentamicin blocking the mechanosensitive channels in stercocilia or degeneration of hair cells Auditory nerve damage Auditory nerve damage Lesion in auditory cortex Lesion in auditory cortex

8. Damaged Hair Cells due to loud sounds 12O dB ; 24 hrs ROCK MUSIC NORMAL HAIR CELLS

9. Tests for Hearing A) Watch Test A) Watch Test B) Tuning fork Tests B) Tuning fork Tests a) Rinne’s Test b) Weber’s Test a) Rinne’s Test b) Weber’s Test c) Schwabach’s test c) Schwabach’s test C) Audiometry C) Audiometry

10. A) Rinnes’s test A) Rinnes’s test Principle: Compares ossicular conduction (air conduction) and bone conduction on the same side Principle: Compares ossicular conduction (air conduction) and bone conduction on the same side B) Webers’s test B) Webers’s test Principle: Compares bone conduction on both sides Principle: Compares bone conduction on both sides C) Schwabach’s test C) Schwabach’s test Principle: Compares bone conduction of patient and normal subject Principle: Compares bone conduction of patient and normal subject

11. Rinne’s Test

12. Weber’s Test

14. Threshold of hearing The threshold of human ear varies with the pitch of the sound The threshold of human ear varies with the pitch of the sound Greatest sensitivity to frequencies between 1000 to 4000Hz Greatest sensitivity to frequencies between 1000 to 4000Hz

15. Methods to quantify hearing thresholds and degree to which hearing loss are Methods to quantify hearing thresholds and degree to which hearing loss are Audiometry: Audiometry: 1. Pure tone audiometry: subject is presented with pure tones of specific frequencies and the minimal intensity at which each frequency is heard is determined 2. Speech audiometry

16. Audiometry Involves determination of hearing threshold for pure tones in the range of 125- 8000 Hz Involves determination of hearing threshold for pure tones in the range of 125- 8000 Hz Results are plotted graphically- AUDIOGRAM Results are plotted graphically- AUDIOGRAM The threshold of human ear is varies with the pitch of the sound The threshold of human ear is varies with the pitch of the sound Greatest sensitivity to frequencies between 1000 to 4000Hz Greatest sensitivity to frequencies between 1000 to 4000Hz

17. Sound frequency, Hz 125 250 500 1000 2000 4000 8000 80 0 100 40 60 20 HEARING LOSS IN dB NORMAL AUDIOGRAM BONE CONDUCTION AIR CONDUCTION

18. Audiogram of old age type- Nerve deafness

19. Audiogram of air conduction deafness

20. Presbycusis Decrease in hearing ability with advancing age, usually seen after the age of 65 Decrease in hearing ability with advancing age, usually seen after the age of 65 Due to loss of hair cells Due to loss of hair cells Hair cells responding to high frequency sounds are mostly affected Hair cells responding to high frequency sounds are mostly affected

21. Pure tone audiogram: Age related increase in hearing threshold. Condition: This is called presbycusis & is due to loss of hair cells and neurons.

22. Brain stem auditory evoked potentials Stimulus: sound of known frequency and intensity presented with ear phones Stimulus: sound of known frequency and intensity presented with ear phones Recording: from active electrodes in vertex of skull Recording: from active electrodes in vertex of skull Responses: the responses are weak and are therefore averaged to eliminate background noise Responses: the responses are weak and are therefore averaged to eliminate background noise Audiometric threshold: Minimum sound intensity required to obtain a clear waves Audiometric threshold: Minimum sound intensity required to obtain a clear waves Interpretation: Waves I-V indicate excitation of structures up to the brain stem; latency < 10 ms; these are used to test the auditory pathway up to the inferior colliculus Interpretation: Waves I-V indicate excitation of structures up to the brain stem; latency < 10 ms; these are used to test the auditory pathway up to the inferior colliculus

23. Brain stem auditory evoked potentials (BAEP)

24. BAEP tests evaluate how the nervous system, specifically the brainstem, responds to specific sounds. BAEP tests evaluate how the nervous system, specifically the brainstem, responds to specific sounds. BAEP tests are used to evaluate acoustic neuromas, brain stem tumors, hearing disorders, coma, brain death, and demyelinating diseases. BAEP tests are used to evaluate acoustic neuromas, brain stem tumors, hearing disorders, coma, brain death, and demyelinating diseases. To evaluate hearing loss in infants, small children, and other patients who are unable to give voluntary subjective responses to traditional hearing tests To evaluate hearing loss in infants, small children, and other patients who are unable to give voluntary subjective responses to traditional hearing tests

25. Otoacoustic emissions (OAE) The primary purpose of otoacoustic emission (OAE) tests is to determine cochlear status, specifically hair cell function The primary purpose of otoacoustic emission (OAE) tests is to determine cochlear status, specifically hair cell function The normal cochlea does not just receive sound; it also produces low-intensity sounds called OAEs, probably by the cochlear outer hair cells as they expand and contract. The normal cochlea does not just receive sound; it also produces low-intensity sounds called OAEs, probably by the cochlear outer hair cells as they expand and contract. Using extremely sensitive low-noise microphones these sounds can be recorded Using extremely sensitive low-noise microphones these sounds can be recorded

26. Uses of OAE’s Uses of OAE’s (1) Screening hearing (particularly in neonates, infants) (1) Screening hearing (particularly in neonates, infants) (2) Partially estimate hearing sensitivity within a limited range (2) Partially estimate hearing sensitivity within a limited range 3) Differentiate between the sensory and neural components of sensorineural hearing loss 3) Differentiate between the sensory and neural components of sensorineural hearing loss The information can be obtained from patients who are sleeping or even comatose because no behavioral response is required The information can be obtained from patients who are sleeping or even comatose because no behavioral response is required