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Audiometry

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  1. Audiometry Dr. Vishal Sharma

  2. Pure Tone Audiometer

  3. 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.

  4. Symbols used in audiogram

  5. Normal Audiogram

  6. Pure Tone Average Calculated by taking arithmetic mean of air conduction thresholds at 500, 1000 & 2000 Hz (speech frequencies)

  7. Classification of Deafness: Goodmann & Clark

  8. Conductive deafness

  9. Sensori-neural deafness

  10. Mixed deafness

  11. Diagnosis of type of deafness

  12. Low frequency conductive HL Otitis media with effusion

  13. Carhart’s notch (otosclerosis)

  14. High frequency SNHL Presbyacusis, ototoxicity, acoustic neuroma

  15. Low frequency SNHL (Meniere)

  16. Deafness in Meniere’s disease

  17. Acoustic dip (Noise deafness)

  18. 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

  19. 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.):Percentageof phonetically balanced (single syllable) words correctly identified at 40 dB above S.R.T.

  20. 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.

  21. Speech Audiogram

  22. Speech Discrimination

  23. Special Audiological Tests

  24. 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

  25. 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. • 70-100 % in cochlear deafness • 0-20 % in conductive & nerve deafness

  26. 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.

  27. Laddergram in A.B.L.B. test

  28. 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

  29. Interpretation

  30. Impedance Audiometry

  31. Impedance Audiometer Probe A = oscillator (220 Hz). B = air pump C = microphone to pick up reflected sound

  32. 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.

  33. Tympanogram parameters

  34. Tympanogram Types (Jerger)

  35. Types of Tympanogram

  36. Type A

  37. Type As

  38. Type Ad

  39. Type B (fluid in middle ear) EAC volume = 1.8 ml

  40. Type B (T.M. perforation, grommet) EAC volume = 3.2 ml

  41. Type B (E.A.C. obstruction) EAC volume = 0.4 ml

  42. Type C

  43. Acoustic Reflex Loud sound > 70 dB above hearing threshold, causes B/L contraction of stapedius muscles, detected by tympanometry as se in compliance.

  44. 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

  45. B/L reflexes present

  46. Stapedial reflex absent

  47. Acoustic Reflex Decay

  48. 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