Pure Tone Audiometry

1. DR.PRASANNA DATTA.

2. PURETONE SOUND

 When an object vibrates in fixed single
frequency, the sound waves will present a
sinusoidal wave pattern knownassine-wave.
 Thesound sensation produced by sucha
sine-wave is called asapure tone sound.
In pure tone audiometry, we test the
hearing sensitivity of asubject only for pure
tone sounds.

4. AIMS OF PURE TONE AUDIOMETRY
 Whether the subject hasany definite hearing
loss.
 Whether the hearing loss is
conductive/sensorineural/mixed type.
 In sensorineural deafness,wheatherthe
deafness is cochlear orretrocochlear.
 Tonote the degree of hearing dysfunction.

5. PURE TONE AUDIOMETER
 It is the electronic deviceused for creating pure
tone audiogram.
 It consists of an audio-oscillator which generates
pure tone soundsof different frequencies.
 Eachtone can be separately amplified to a
maximum of 100to 110dB 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.

7. THRESHOLD
 The International Standards Organisation has
defined hearing threshold as“the lowest sound
pressure level, at which under specified
conditions, aperson gives apredetermined
percentage of correct responses on repeated
trails”.
 For clinical usage, thispredetermined
percentage is50%.
 In pure tone audiometry,we try to obtain
thresholds that compare the hearing sensitivity

8. THRESHOLD
 of asubject in decibels with afixed ideal or
normal hearing level(0dB).
 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 hearingthreshold.

9. DECIBEL & OTHER
RELATED TERMS
 TheDecibel isthe unit by which the intensity
of the sound(or pressure exerted by asound
stimulus) ismeasured.
 Average minimum which will producea
sound just audible to anormal ear:-
 In units of pressure0.00024 dynes/sq.cm.
 In units of intensity 1/100000000000000000
watts/sq.cm.

10. DECIBEL & OTHER
RELATED TERMS
 BEL-Aratio expressedin logarithm(with base
10)which tells ushow many times the sound
we are measuring is stronger or weaker than
areferencesound.(0-14)
[BEL=log IO/IR]
 DECIBEL-one tenth ofBEL.
[DECIBEL(dB)=10 logIO/IR]
 SPL-signifies that apressure reference has
been used(i.e. referencesound has apressure
level of .00024dynes/sq.cm.)

11. DECIBEL & OTHER
RELATED TERMS
 HL-In different frequencies the intensity or
the pressure of just audible sound is slightly
different. Hencefor 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 as0 dB HL, for that particular
frequency.

12.  SL-This is in reference to the auditory
threshold of aparticular subject & indicates
how much sound sensation that particular
subject is actuallygetting.
SL+handicap=HL.
DECIBEL & OTHER
RELATED TERMS

13. PROCEDURE OF P.T.A.
 AIRCONDUCTIONTESTS(conditions
required):-
 1.CALIBRATIONOFTHEINSTRUMENT-
 ISO-1964specification.
 6 monthly electroniccalibration.
 Air conductionheadphones-TDH39/TDH49.
 Insert ear-phones-ER-3A.
 Ear conductionhead phone cushions-MX 41
AR.

17. PROCEDURE OF P.T.A.
 2.REASONABLYNOISELESSTEST
ENVIRONMENT-
 American standardsAssociation(ANSI-53.1-
1991)table.
 ISO/DIS 8253table.
 3.POSITION OFHEADPHONES.
 4.INSTRUCTIONTOTHEPATIENT.

18. PROCEDURE OF P.T.A.
 TECHNIQUEOFAIRCONDUCTIONTESTS:-
 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 8253technique.

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

21. PROCEDURE OF P.T.A.
 Area over which the person canhear the sound
loudest isplaced.
 The testing ear is kept uncovered.The other ear
is kept covered formasking.
 The bone conduction vibrator must not touch
the pinna or the earphone.
 b)Frontal placement-Superior in respect of
consistency because of lessvariation of amount
of tissue between bone conduction vibrator &
the earphone.
 TECHNIQUESOFBONECONDUCTION.

22. 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 beover-emphasised.
 Contralateral masking means introducing a
noisein non-test ear,suchthat the non-test
ear is acoustically blocked & can not
participate in the hearing test.

23. MASKING
 When to mask:-
 Interaural attenuation(40-45 dBHLfor air
conduction).
 Hazard of crosshearing is much more in bone
conduction than in air conduction test.
 Chanceof cross-hearing isAC(testear)-
BC(non-test ear)>IA.
 Forbone conduction, the Interaural
attenuation may be 0 dBHL.

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

25. MASKING
 Masking is doneby:
 1.Whitenoise-consistsof soundof all
frequenciesfrom high to low.
 2.Narrow bandnoise-more effective for
masking, consists of anarrow band of
noise 100-200 Hz above/below that
frequency.
 3.Complex noise-low frequency
fundamental+multiples offrequencies up
to 4000 Hz.Least efficient for masking.

26.  A) QUANTITATIVEINFORMATION-
 1.What is theACthreshold?
 2.What is theBCthreshold?
 3.What is theA-B gap?
 4.Wheather masking hasbeen done or not?
 5.Doesit match with clinical findings and
tuning forktests?
 B)QUALITATIVEINFORMATION.
INTERPRETETION OF P.T.A.

27. PTA OF CONDUCTIVE
DEAFNESS

28. PTA OF SENSORINEURAL
DEAFNESS

29. PTA OF MIXED
DEAFNESS

30. CONDUCTIVE DEAFNESS
ACthreshold>30dB.
BCthreshold<20 dB.
A-B gap>25dB.

31. SENSORINEURAL DEAFNESS
ACthreshold>30 dB.
BCthreshold>20 dB.
A-B gap<20dB.

32. MIXED DEAFNESS
ACthreshold>45 dB.
BCthreshold>20 dB.
A-B gap>20dB.

33. CONDUCTIVE DEAFNESS IN
OSSICULAR
DISCONTINUITY

34. CARHART’S
NOTCH(OTOSCLEROSIS)

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

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

37. LIMITATIONS OF P.T.A.
 1.AUDIOGRAMSAREVERYOFTEN
INACCURATE.
 a)Improper technique- masking,placement.
 b)Improper testcondition-RNTE.
 c)Improper test instrument-calibration.
 d)Improper examiner.
 2.ASUBJECTIVE&TIME-CONSUMINGTEST.
 3.ITDOESNOTASSESSALLFEATURESOF
HEARING.

38. LIMITATIONS OF P.T.A.
 4.ITDOESNOTIDENTIFYTHENATUREOF
THEPATHOLOGY.
 5.BONE CONDUCTIONTESTDOESNOT
ASSESSTHETRUESENSORINEURAL
RESERVE.
 6.MANY SOURCESOFVARIANCESIN THE
TESTRESULTSTHATARENOTRELATEDTO
HEARING.

39. HAVE A GOOD DAY