lecture 3 (introduction to pure tone audio me try)

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Pure Tone Audiometry

Lecture 3



References

• Audiology Diagnosis – Chapter 11 (Pure Tone Tests)

• Lecture Notes



Topics

• Pure tone audiometry

Definition and purposes

•

Audiometer Definition & types

Audiometer components

Calibration of audiometers

Calibration schedules

• Audiogram and audiometric symbols




• Definition:

The procedure by which sensitivity thresholds for each ear areobtained for pure tone stimuli of different frequencies (250,

500, 1000, 2000, 4000 & 8000 Hz)




• Threshold Level:

The lowest intensity level at which the patient is able to respond to the

stimulus 50% of the time

Stimulus: anything that can elicit or evoke a response in an excitable

receptor

i.e. stimulus = signal (pure tone or noise) – excitable receptor = ear /

hearing system

50 % means the patient must respond to two out of four or three out of

six trials




• Purposes:

Results from pure tone audiometry are used to make the initial diagnosis

of hearing impairment (normal/abnormal hearing sensitivity)

In the case of abnormal hearing sensitivity, the results would help in thediagnosis of the type and degree of hearing impairment

It assist in the determination of (re)habilitation services needed to assisthearing impaired persons




• Audiometer

The instrument used in pure tone testing

Electronic instrument used to quantify hearing sensitivity

Have frequencies with a scale based on the octave and half-octave

frequencies of 125, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 6000,

and 8000 Hz.




• Audiometers Types:

Standard Pure Tone and Automatic/Microprocessor Audiometers

Diagnostic Audiometers

Extended High-Frequency Audiometers

Free-Field Equivalent Audiometers



Audiometers Types

• Standard Pure Tone and Automatic/Microprocessor Audiometers:

Used for screening or basic threshold testing

Manual audiometers are operated by the examiner

Automatic audiometers are controlled by a system with a hand held switch

Commonly used for mass screening (i.e. industrial hearing conservationprograms) to save time

Have limited value in testing children and in diagnostic testing



Standards Pure Tone Audiometer

(Manual Screening Audiometer)



Audiometers Types

• Diagnostic Audiometers

Includes a wide variety of features; bone conduction testing, speechtesting through monitored live voice or recorded presentations, maskingstimuli and site of lesion testing

• Extended High-Frequency Audiometers

To measure hearing thresholds from 8000 Hz to 16,000 Hz

Application: to monitor onset of possible high frequency HL from ototoxicmedications



Clinical Diagnostic Audiometers



Audiometers Types

• Free-Field Equivalent Audiometers

Calibrated so the output of the earphones or bone oscillator can beexpressed in terms of equivalent hearing as if the sound was presented at

0 degrees azimuth in the sound field

The output from free field equivalent audiometers is expressed in SPL(sound pressure level)

Good to comparison of performance for hearing aids



Audiometer Components



Calibration Of Audiometers

• Calibration Of Audiometers

Calibration is necessary to ensure that the audiometer is producing a pure

tone at the specified frequency and intensity

The stimulus is present only in the earphone to which it is directed

The stimulus is free from unwanted noise, the interference, and distortion



Calibration Schedules

• Four types of audiometer check/calibration schedules:

Daily listening check

Psychoacoustic (Biological) check

Periodic electronic calibration

Exhaustive electronic calibration



Daily Listening Check

In the morning after warm up (10 min)

Signal is checked at various intensities and at all frequencies

Look for transient clicks or distortion (undesired acoustic signal)

Ensure that signal is delivered to the correct earphone

No cross talk is present (cross talk: when the signal intended for exclusive

routing to one earphone is also routed to the other)



Psychoacoustic (Biological) Check

At least once per month

The output from the audiometer is checked

This process is done either with:

A. Psychoacoustic (biologic) check

OR

A. Electroacoustical calibration check with a sound level meter



A. Psychoacoustic (Biologic) check

• Obtain baseline thresholds on 3-5 normal hearing individuals who will beavailable for comparison testing throughout the year

• If on the monthly check, a threshold difference > 5 dB HL is found for one

of the individuals for any test frequency between 500-6000 Hz, the othersubjects should be checked

• If a shift > 5 dB HL in the same direction is confirmed, an electriccalibration of the audiometer is required

• Monthly results should recorded in a form



B. Electroacoustical Calibration Check

Performed with sound level meter and real-ear coupler

Measurements are obtained directly from the audiometer earphone at afixed attenuator setting and compared with the expected ANSI 1996reference equivalent threshold SPL value

If the difference is > 3 dB, the audiometer would require electroniccalibration

Sound level meter: an electronic instrument designed to measure soundintensity in dB in accordance with an accepted standard

ANSI (American National Standards Institute): association of specialists,manufacturers, and consumers that determines standards for measuringinstruments, including audiometers



Periodic Electronic Calibration

At least one each year

To make sure that the audiometer is meeting the minimum

standards defined by ANSI S3.6-1996



Exhaustive Electronic Calibration

Every 5 years

More comprehensive than the periodic electronic calibration

Includes testing of all settings on the frequency and intensity dials

Replacing switches, cords, earphone drivers and cushions



The Audiogram

Displays data from the audiological evaluation

Frequency (in Hz) is displayed on the horizontal axis

Intensity (in dB HL) is displayed on the vertical axis

Audiogram form either records both right and left ear information on onegraph (ASHA Form) or each ear in different form



The Audiogram



Audiometric Symbols

• Air conduction:

• Response in right ear (red)

unmasked: O

Masked :

• Response in left ear – (Blue)

Unmasked: X

Masked:

• Sound Field (Speakers):

S (sound field) OR F (free

field)



Audiometric Symbols

• After all thresholds are plotted on the audiogram, the symbols are

connected with a:

Solid red line for the right ear

Solid blue line for the left ear



Audiograms Forms

Right ear (RE) & left ear (LE) results plottedon two separate audiograms

Right ear (RE) & left ear (LE) resultsplotted on the same audiogram

lecture 3 (introduction to pure tone audio me try)

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