n drtbalus otolaryngology online Introduction Pure tone audiometry is used to measure auditory threshold of an individual The instrument used in this measurement is known as the audiometer This is a subjective investigation the accuracy of which is dependent on the response of the patient ID: 774657
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Pure tone audiometry
Balasubramanian Thiagarajan
drtbalu's otolaryngology online
Slide2Introduction
Pure tone audiometry is used to measure auditory threshold of an individualThe instrument used in this measurement is known as the audiometerThis is a subjective investigation, the accuracy of which is dependent on the response of the patient
drtbalu's otolaryngology online
Slide3Audiometer
This has been defined by International Electrochemical Commission 1976 as an instrument used to measure the acuity of hearing and auditory threshold.
There are two types of audiometers: subjective and objective ones.Pure tone audiometer – subjectiveImpedance / BERA - Objective
drtbalu's otolaryngology online
Slide4Pure tones
Simplest of all soundsSpecific and single frequencyDescribed by their frequency, amplitude, phase and durationPure tone amplitude is quantified in decibelPure tone audiometry provides information about the type of hearing loss and also helps in quantifying frequency specific threshold elevation.Increase in stiffness of middle ear causes low frequency hearing loss, where as increase in mass effect of middle ear causes high frequency hearing loss
drtbalu's otolaryngology online
Slide5Features of an audiometer
It generates pure toneFrequency of the tone generated can be selectedIntensity of the tone generated can be selectedIt has the ability to route tonal stimuli to either earTone generated may be of intermittent / continuous type. This is controlled by the presence of an interrupter switch
drtbalu's otolaryngology online
Slide6Types of pure tone audiometers
Type I audiometer – Full fledged audiometer Type II audiometer – Does not have speakers hence free field audiometry is not possible with this.Type III audiometer – Portable audiometer without speech audiometry facilityType IV audiometer – Basic screening audiometer. Has only ear phones
drtbalu's otolaryngology online
Slide7Type I audiometer
Most comprehensive equipmentIt can measure air conduction thresholds between 125 – 8,000 Hz and bone conduction threshold ranging between 250 – 6000 HzMaximum intensity for air conduction threshold is 120 dB and bone conduction maximum intensity is about 50 dB lower than this value. Bone oscillators produce distortions above this level.
drtbalu's otolaryngology online
Slide8Components of an audiometer
OscillatorInterrupter switchEqualization circuitOutput power amplifierHearing level attenuatorOutput transducers
drtbalu's otolaryngology online
Slide9Oscillator
This generates pure tonesIts accuracy ranges between +/- 3% within the specified frequency rangeFrequencies generated include 125, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 6000, and 8000 Hz.These sounds are electronically generated
drtbalu's otolaryngology online
Slide10Interrupter switch
Tones should be either switched on or off.Continuous tone undergoes decayPatient fatigability should also be consideredIt controls the duration of signal presented to the patientIt is typically in off position when pure tones are presented and can be turned on only on pressing the button.It is typically in on position for speech signal
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otolaryngology online
Slide11Equalization circuit
This contains resistors which help in equalization of sound generatedHuman threshold for various frequencies are variableHuman ear is highly sensitive to 2Khz frequencyIt is insensitive to high and low frequencies.
drtbalu's otolaryngology online
Slide12Output power amplifier
Signals produced by oscillator needs to be amplifiedThis amplifier produces very little distortionIt has a good signal to noise ratio
drtbalu's otolaryngology online
Slide13Hearing level attenuator
It controls the level of signal from the audiometer within 110-120 dBThe intensity can be varied in steps of 5 dBAttenuator steps should be very accurate
drtbalu's otolaryngology online
Slide14Output transducers
Ear phonesBone vibratorLoud speaker
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Slide15Head phones
Used to test pure tone Air conduction thresholds
These are supra-aural ear phonesShould always be calibrated before useThis type of supra aural ear phones are easy to calibrateIt has a flat frequency responseDelivers high output sounds
drtbalu's otolaryngology online
Slide16Bone vibrators
These have a limited dynamic frequency range
At low frequencies vibrators show distortionsPure tone bone conduction thresholds can me measuredPlaced over mastoid process (8-15 dB lower thresholds)
drtbalu's otolaryngology online
Slide17Loud speakers
Used in free field audiometryUsed to test infants and childrenCan be used to perform behavioral audiometry
drtbalu's otolaryngology online
Slide18calibration
Used to define audiometric zeroCalibration involves calibration of audiometer, ear phones and bone vibratorsCan be performed using human volunteers and artificial ears
drtbalu's otolaryngology online
Slide19protocols
Should be tested in sound proof roomClaustrophobic patients should be handled with carePatients with collapsed ear canal should be tested using special ear phonesMalingerer’s should be tested only by an audiologistPt should be seated comfortablyOtoscopy should be done prior to audiometryTest procedure should be fully explained to the patientGlasses / ear rings should be removed
drtbalu's otolaryngology online
Slide20Placement of head phones
Red head phone is placed over right ear
The diaphragm is placed over ear canalIt should fit snuglyHead band should not be tight
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Slide21familiarization
Testing is begun at 1000 Hz and 30 dBAt this frequency the testee is likely to have residual hearing. At this frequency testing retesting response is reliableTesting usually begins with the examinee’s self reported better ear, to decide whether masking is necessary for testing the other earPulsed tone is used
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Slide22Hughson - Westlake ascending technique
Up 5 and down 10 methodTones of short duration is usedBetter ear is tested to decided whether masking is necessaryStarted at 1000 Hz at a level above threshold. This frequency is selected because it is an important frequencyIn pts with profound hearing loss the test should be started with 250 Hz because these patients have residual hearing only in low frequenciesStimulus is started at 0 dB and increased in steps of 10 dB till the patient respondsOn positive response the volume is decreased by 10 dB. If the pt responds it is decreased by 10 dB and repeated till he does not respondOn no response the intensity is increased by 5 dB till the pt confirms hearing the toneThis should be repeated till the pt gives positive response in two out of three attempts at the same dB levelTone presented should last between 1-3 seconds
drtbalu's otolaryngology online
Slide23Plotting
The readings are plotted with red color indicating right side
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Slide24Audiogram chart
chart
Legend
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Slide25Degree of hearing loss
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Slide26Factors affecting reliability
Poor test instructionsImproper headphone placementRhythmic tone presentationClues from examiner
drtbalu's otolaryngology online
Slide27Environmental factors affecting reliability
Excessive background noisePoor ventilationPoor lightingInvalid equipment calibration
drtbalu's otolaryngology online
Slide28Comparison of audiograms
drtbalu's otolaryngology online
Slide29Types of audiogram
drtbalu's otolaryngology online
Slide30Some audiogram types
drtbalu's otolaryngology online
Slide31drtbalu's otolaryngology online
Thank you
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