PURE TONE AUDIOMETRY for assesment of hearing

pta is subjective test,term used in pta bone conduction ,air conduction

1. PURE TONE AUDIOMETRY \

2. TERMS USED IN PTA FREQUENCY - Number of cycles per second,measured in Hertz (Hz) PITCH- Subjective sensation produced by frequency of sound INTENSITY - It is strength of sound which determine its loudness measured in DECIBELS LOUDNESS It is subjective sensation of intensity AIR CONDUCTION - When sound given through external ear.e.g headphone,insertphone BONE CONDUCTION When sound given through mastoid process .e.g.bone vibrator

3. HEARING THRESOLD threshold of hearing is defined as the stimulus level giving rise to 50% or more correct detection responses, or a minimum of two out of two, three or four ascending presentations PURE TONES S ound produced by a sine wave at a single frequency. PURE TONE AVERAGE Average of air conduction thresold obtained at 500,1000 and 2000Hz in one ear OCTAVE - Interval between one musical pitch and another with double or half of its frequency

4. AIMS to find out any hearing loss or not degree of hearing dysfunction type of hearing loss conductive/sensorineural/mixed Compare serial audiograms (pre- and post-treatment audiograms) to decide on the appropiate rehabillation device which can be used to minimise hearing disability

5. PURE TONE AUDIOGRAM Result plotted graphically called pure tone audiogram Instrument used to measure is called pure tone audiometer. The range of normal human hearing is 20- 20,000 HZ. The graph plotted in x –axis frequency in hertz are 250,500, 1000,2000,4000 & 8000 (cycles per second ).  In y –axis hearing loss in decibels from -10 to 110 db HL . where 0 dB HL represents the average threshold for otologically normal young individuals at each frequency .

6. COMPONENT OF PTA Oscillator to generate pure tone Masking dial:Oscillator to generate tone(made use for masking) Frequency dial(125-8000Hz) intensity dial(10-120dB) Transducer:changes acoustic to electrical energy bone conduction(single)-BC vibrator Air conduction(two-one for left and one for right):headphone Interrupter switch:switch to give the tone Power switch/on and off switch

7. COMP0NENTS OF AUDIOMETER Oscillator to generate pure tone Masking dial : Oscillator to generate noise(made for masking) Frequency dial (125-8000Hz) Intensity dial (10-120dB) Transducer -change acoustic to electrical energy Interrupter switch -switch to give tone Power switch /On and Off switch

8. TRANSDUCER AIR-CONDUCTION TRANSDUCERS- supra-aural headphone. circum-aural headphone insert earphones BONE-CONDUCTION TRANSDUCERS Radioear B-71 ( bone vibrator )

9. AIR-CONDUCTION TRANSDUCERS supra-aural headphone - rest on the surface of the pinna without enclosing the pinna in their cups . air conduction transudcer first place on better ear . airleaks can occur .

10. circum-aural headphone , encloses the pinna in its cups. prevent leakage of the test signal or ambient noise from the test environment, reduce the amount of physiological noise in the ear

11. INSERT EARPHONE - two probes (right and left) covered by a disposable foam tip that is placed in the ear canals for testing G ive improved attenuation of ambient noise relative to supra-aural headphones, and reduced likelihood of infection transmission as inserts are single use . positioning of the insert reduces the likelihood of the ear canal becoming collapsed in children or elderly ears.

12. reduce vibrotactile stimulation when delivering high-level low-frequency tones. They also have a higher interaural attenuation’ compared to supra- and circum-aural headphones

13. BONE CONDUCTION TRANSDUCER The most commonly used BC transducer for clinical audiometry is the Radioear B-71. The transducer is held at one end of a rigid vertical headband. The opposite end has no transducer attached and serves only as support. Note that the transducer is not touching the hair or pinna

14. The BC transducer is placed first on the mastoid prominence of the worse-hearing ear first . The transducer must be placed so that it is as close as possible to the pinna, without touching it and avoiding the hair . testing is generally done for frequencies between 500 Hz and 6000 Hz.

15. PROCEDURE- AIR CONDUCTION TEST Calibration of instrument A reasonably noiseless test environment.  Position of headphones  Instructions to the patient.  Technique of air conduction test- First is Conventional method Hughson-Westlake technique,ASHA

16.  CALIBRATION OF INSTRUMENTS ISO – 1964 Specifications for calibration  Electronic calibration – atleast once in 6 months  Biological calibration – should be done each day before the audiometer is used. 

17. A REASONABLY NOISELESS TEST ENVIRONMENT  M aximum permissible ambient noise for the different frequencies required for air and bone conduction tests.  Air Conduction - 25 - 30 db ,  Bone Conduction - 10 -15 db The examiner sits outside and the patient inside the audiometric booth.The booth has a window that allows the examiner to see the patient.

18. POSITION OF HEADPHONES Diaphragm of headphone – over the opening of EAC No wax , discharge , cotton in EAC  Collapse of ear canal – supraaural earphones / headphones are placed over ear – Cause small Air- Bone gap.

19. INSTRUCTION TO PATIENT Test needs should be thoroughly explained.  Little time spent in getting acquainted with the patient and his problems prior to the test , helps in establishing a rapport.

20. TECHNIQUES - CONVENTIONAL METHOD (HUGHSON-WESTLAKE ) A detailed clinical history & examination should precede the test. Better ear is tested first , start with 1000 Hz & then 2k,4k,8k,then 500 , 250 Hz. first familiarises the patient with the tone by introducing sound at arbitrarily presumed suprathresold level . if the patient hears the tone then Tones are lowered in 10 d B steps till patient stops hearing .

21. then increased in 5 d B steps till patient hearing thresold obtained ,when one gets atleast 3 out of 5 responses correct Second ear – may start with last frequency used to test the first ear ( no need to start with 1000 Hz )  5-up-10-down ( tones are lowered in 10 db steps and increased in 5 db steps )

22. ASHA METHOD(AMERICAN SPEECH-LANGUAGE HEARING- ASSOCIATION)

23. BONE CONDUCTION COMPRESSIONAL / DISTORTIONAL BONE CONDUCTION Vibratory energy ( Sound ) reaches the cochlea Alternate expansion and compression of cochlear shell (due to flexiblity of round window memb and cochlear equeduct) Movement of cochlear fluid Displacement of basilar membrance Leads to changes that result ultimately in sound being heard

24. INERTIAL BONE CONDUCTION Vibratory energy ( Sound ) strikes the skull Sets the skull into vibration Ossicles in middle ear lag behind & do not move due to inertia of ossicles Sets up relative motion b/w footplate of stapes & cochlear fluid deep to oval window Vibration of cochlear fluid

25. OSSEO-TYMPANIC BONE CONDUCTION Vibratory energy ( Sound ) reaches the skull Skull starts vibrating Sets into vibration the column of air in EAC Partially transmitted to TM Thro’ the ossicles in the middle ear To Cochlear fluid of inner ear ( like air - conducted sound)

26. PROCEDURE - BONE CONDUCTION Calibration of instrument  Reasonably noiseless test environment  Placement of bone conduction vibrator  Instructions to the patient  Technique – same as air conduction. P LACEMENT OF BONE CONDUCTION VIBRATOR M astoid P lacement F rontal P lacement

27. MASKING Noise presented to the non-test ear to prevent it from responding to a signal presented to the test ear WHEN TO MASK All bone conduction When air conduction more than 45 db HL Cross – hearing in air conduction if AC ( test ear ) – BC ( non test ear ) > IA But when we are testing air conduction of test ear we are not aware of BC thresold of non test ear ,so we assumed it normal 0dB

28. CROSS HEARING IN AC CROSS HEARING IN BC

29. Over masking If the masking sound used is so loud thai it crosses over from the non- test ear and obliterates or mask the test signal in test ear , the subject will not hear the test signal in the test ear until it is much above the actual threshold.  Under masking  Undermasking leads to false A-B gaps and is usually the result of operator inexperience or a failure to follow masking rules.

30.  MASKING DILEMMA  In pts with b/l moderate to severe CHL ( large AB Gap ) , the plateau in Hood’s plateau method of masking may be unidentifiable.  Max and Min masking may be equal (or) min masking may become more than max masking

31. SOUNDS USED FOR MASKING WHITE NOISE  Broadband or wideband noise ( equal amt of sound of all frequencies , starting from low to very high frequencies ) NARROW BAND NOISE  Narrow band of noise centered on test tone freq. with 100 – 200 Hz above and below that freq.  COMPLEX NOISE  Low freq. fundamentals plus the multiples of that freq upto 4000Hz

32. INTERPRETATION OF AUDIOGRAM 0-25 db - Normal 26-40 db - Mild deafness 41-55 db - Moderate deafness 56-70 db - Severe deafness 71-90 db - Very severe deafness Above 90 db - Profound deafness

33. AUDIOGRAM Normal hearing BC line in audiogram is above AC line with both bone conduction and air conduction within normal range of hearinG( 0-25dB) with A-B gap 10-15 dB

34. -CONTINUE CONDUCTIVE DEAFNESS The bone conduction is normal and the air bone gap more than 20dB

35. SENSORINEURAL DEAFNESS- the bone conduction is below normal and the air bone gap is 15 dB or less

36. MIXED HEARING LOSS - The bone conduction more than 20dB with air bone gap is more than 20dB

37. conductive deafness showing large air bone gap at higher frequencies in case of otitis media with effusion

38. CARHART’S notch at 2000hz in BC in case of moderate conductive deafness due to otosclerosis

39. Conductive deafness with very large air bone gap (55dB ) in case ossicular discontinuity

40. a flat audiogram in case of sensorineural hearing loss . audiogram called flat if there is less than 10dB increase or decrease in hearing per octave flat audiogram in sensorineural defness suggest atrophy of stria vascularis Strial presbycusis,salicylate poisoning etc.

41. Decending audiogram caused by sensorineural deafness caused by damage in oragan of corti by ototoxic drug

42. sensorineural deafness most marked at 4000Hz in case of acoustic trauma. at 4000 Hz a notch called a acoustic notch

43. Sensorineural deafness moderate degree more marked at lower frequencies in case of early enolymphtic hydrops called rising type of curve

44. Sensorineural deafness moderate degree more marked at higher frequencies in case of late enolymphtic hydrops called falling type of curve

45. Trough shaped curve in case of congenital sensorineural hearing loss(B/L) to be labelled Trough shaped there has to be 20dB or more loss at 1000-2000 Hz ( but not at lower of higher frequencies)

46. MY REFERENCES- SCOTT-BROWN’S CUMMING’S ANIRBAN BISWAS