CHAPTER SEVEN
OAE test procedure
66
OAE test procedure
If the position of the Fit Size Indicator corresponds with the age of the
patient and
Checkfit
is displayed on the top of the screen then the probe
fit and the test conditions are adequate for testing. The
Stimulus and Noise
OK indicators (above the screen) should also be illuminated. Select
Start
to continue the test.
If there is a disagreement between the Fit Size Indicator and the ear
canal size expected of your patient, then there may be a problem with the
probe or the probe fit. For example: an indication of a large ear canal in a
neonate may occur if the probe has fallen out of the ear or if the probe is
blocked; an indication of a small ear canal in an adult may occur because
of wax blocking the canal.
7.4.2
Noise level indicator
A Noise Level Indicator is shown on the right of the
Checkfit
screen. The
bar moves in response to changes in noise. For good testing conditions
the bar should be consistently below the Noise Reject Level which is
represented by the horizontal line across the Noise Level Indicator. The bar
is filled red if the level is above the threshold and green if it is below. The
threshold level is displayed numerically above the indicator. Use the up/
down arrow keys to change the Noise Reject Level.
Generally higher noise reject can give faster data collection but poorer
quality data. The best noise reject setting depends on both test conditions
and the strength of the emission being tested. Strong emissions may be
detected in a noisy environment with a high noise reject threshold. Weak
emissions may only be detected in a quiet environment with a low noise
reject threshold.
7.4.3
Checkfit condition information
Highlighted messages are shown when conditions are not optimum for
OAE recording.
Check Probe Fit
is shown if the stimulus level falls outside the accepted
range.
Noisy
appears if the noise level is consistently above the set noise reject
threshold for a period of time.
Ringing
is displayed when there is obvious oscillation within the
Stimulus
Waveform
after the initial expected positive and negative peaks.