Pure tone audiometry

1. DR.DHIMAN BHATTACHARYYA. 1 ST YEAR PGT,MS(ENT) IPGME&R & SSKMH,KOLKATA. PURE TONE AUDIOMETRY

2. PURE TONE SOUND When an object vibrates in fixed single frequency, the sound waves will present a sinusoidal wave pattern known as sine-wave. The sound sensation produced by such a sine-wave is called as a pure tone sound. In pure tone audiometry, we test the hearing sensitivity of a subject only for pure tone sounds.

3. AIMS OF PURE TONE AUDIOMETRY Whether the subject has any definite hearing loss. Whether the hearing loss is conductive/sensorineural/mixed type. In sensorineural deafness,wheather the deafness is cochlear or retrocochlear. To note the degree of hearing dysfunction.

4. PURE TONE AUDIOMETER It is the electronic device used for creating pure tone audiogram. It consists of an audio-oscillator which generates pure tone sounds of different frequencies. Each tone can be separately amplified to a maximum of 100 to 110 dB in most frequencies except very low & very high frequencies. Audiometer is connected to standard & specified bone conduction vibrator or earphones through which sound is presented to subject’s ear.

5. THRESHOLD The International Standards Organisation has defined hearing threshold as “the lowest sound pressure level, at which under specified conditions, a person gives a predetermined percentage of correct responses on repeated trails”. For clinical usage, this predetermined percentage is 50%. In pure tone audiometry,we try to obtain thresholds that compare the hearing sensitivity

6. THRESHOLD of a subject in decibels with a fixed ideal or normal hearing level(0 dB). So, in clinical audiometry,it is the relative threshold & not the absolute threshold that is measured. That means, in audiological measurements, the intensity of sound is always measured & expressed in comparison to or in relation to another sound which is ideal normal hearing threshold.

7. DECIBEL & OTHER RELATED TERMS The Decibel is the unit by which the intensity of the sound(or pressure exerted by a sound stimulus) is measured. Average minimum which will produce a sound just audible to a normal ear:- In units of pressure 0.00024 dynes/sq.cm. In units of intensity 1/100000000000000000 watts/sq.cm.

8. DECIBEL & OTHER RELATED TERMS BEL-A ratio expressed in logarithm(with base 10) which tells us how many times the sound we are measuring is stronger or weaker than a reference sound.(0-14) [BEL=log IO/IR] DECIBEL-one tenth of BEL. [DECIBEL(dB)=10 log IO/IR] SPL-signifies that a pressure reference has been used(i.e. reference sound has a pressure level of .00024 dynes/sq.cm.)

9. DECIBEL & OTHER RELATED TERMS HL-In different frequencies the intensity or the pressure of just audible sound is slightly different. Hence for standardisation, different amount of pressure(or intensity) have been separately calculated for each frequency, such that the minimum sound audible by a normal subject in different frequencies may be designated as 0 dB HL , for that particular frequency.

10. SL-This is in reference to the auditory threshold of a particular subject & indicates how much sound sensation that particular subject is actually getting. SL+handicap=HL. DECIBEL & OTHER RELATED TERMS

11. PROCEDURE OF P.T.A. AIR CONDUCTION TESTS(conditions required):- 1.CALIBRATION OF THE INSTRUMENT- ISO-1964 specification. 6 monthly electronic calibration. Air conduction headphones-TDH39/TDH49. Insert ear-phones-ER-3A. Ear conduction head phone cushions-MX 41 AR.

12. PROCEDURE OF P.T.A. 2.REASONABLY NOISELESS TEST ENVIRONMENT- American standards Association(ANSI-53.1-1991) table. ISO/DIS 8253 table. 3.POSITION OF HEADPHONES. 4.INSTRUCTION TO THE PATIENT.

13. PROCEDURE OF P.T.A. TECHNIQUE OF AIR CONDUCTION TESTS:- 1.CONVENTIONAL/ HUGHSON-WESTLAKE(5-up-10-down) technique. 2.American Speech & Hearing Association(ASHA) technique. 3.British Society of Audiology/British association of Otolaryngologists technique. 4.ISO/DIS 8253 technique.

14. PROCEDURE OF P.T.A. BONE CONDUCTION TESTS(conditions required):- 1.Calibration of the instrument-Radio ear B71. 2.Reasonably noiseless test environment. 3.Placement of bone conduction vibrator- a)Mastoid placement- Superior in respect of sensitivity by 10-15 dB. The bone conduction vibrator is placed over the mastoid bone attached to a spring metal headband. The pressure on mastoid is given as 500 gm/sq.cm.

15. PROCEDURE OF P.T.A. Area over which the person can hear the sound loudest is placed. The testing ear is kept uncovered. The other ear is kept covered for masking. The bone conduction vibrator must not touch the pinna or the earphone. b)Frontal placement-Superior in respect of consistency because of less variation of amount of tissue between bone conduction vibrator & the earphone. TECHNIQUES OF BONE CONDUCTION.

16. MASKING In pure tone audiometry, the clinician must ascertain the exact hearing threshold by air & bone conduction for the different frequencies for each of the two ears separately & individually. This can not be taken lightly & needs to be over-emphasised. Contralateral masking means introducing a noise in non-test ear, such that the non-test ear is acoustically blocked & can not participate in the hearing test.

17. MASKING When to mask:- Interaural attenuation(40-45 dB HL for air conduction). Hazard of cross hearing is much more in bone conduction than in air conduction test. Chance of cross-hearing is AC(test ear)-BC(non-test ear)>IA. For bone conduction, the Interaural attenuation may be 0 dBHL.

18. MASKING How much to mask-neither undermask,nor overmask. Minimum masking level: (AC)Air conduction threshold in the test ear-45+(Air conduction threshold in the masked ear-Bone conduction threshold in the masked ear). Maximum masking level: Bone conduction threshold for the test ear+45.

19. MASKING Masking is done by: 1.White noise-consists of sound of all frequencies from high to low. 2.Narrow band noise-more effective for masking, consists of a narrow band of noise 100-200 Hz above/below that frequency. 3.Complex noise-low frequency fundamental+multiples of frequencies up to 4000 Hz. Least efficient for masking.

20. A) QUANTITATIVE INFORMATION- 1.What is the AC threshold? 2.What is the BC threshold? 3.What is the A-B gap? 4.Wheather masking has been done or not? 5.Does it match with clinical findings and tuning fork tests? B)QUALITATIVE INFORMATION. INTERPRETETION OF P.T.A.

21. PTA OF CONDUCTIVE DEAFNESS

22. PTA OF SENSORINEURAL DEAFNESS

23. PTA OF MIXED DEAFNESS

24. CONDUCTIVE DEAFNESS AC threshold>30dB. BC threshold<20 dB. A-B gap>25 dB.

25. SENSORINEURAL DEAFNESS AC threshold>30 dB. BC threshold>20 dB. A-B gap<20 dB.

26. MIXED DEAFNESS AC threshold>45 dB. BC threshold>20 dB. A-B gap>20 dB.

27. CONDUCTIVE DEAFNESS IN OSSICULAR DISCONTINUITY

28. CARHART’S NOTCH(OTOSCLEROSIS)

29. STRIAL PRESBYACUSIS(S.N.D.)

30. S.N.D. D/T ACOUSTIC TRAUMA

31. LIMITATIONS OF P.T.A. 1.AUDIOGRAMS ARE VERY OFTEN INACCURATE. a)Improper technique- masking, placement. b)Improper test condition-RNTE. c)Improper test instrument- calibration. d)Improper examiner. 2.A SUBJECTIVE & TIME-CONSUMING TEST. 3.IT DOES NOT ASSESS ALL FEATURES OF HEARING.

32. LIMITATIONS OF P.T.A. 4.IT DOES NOT IDENTIFY THE NATURE OF THE PATHOLOGY. 5.BONE CONDUCTION TEST DOES NOT ASSESS THE TRUE SENSORINEURAL RESERVE. 6.MANY SOURCES OF VARIANCES IN THE TEST RESULTS THAT ARE NOT RELATED TO HEARING.

33. HAVE A GOOD DAY THANK YOU