Interacoustics Eclipse Additional Information page 216

Eclipse Additional Information
 Preamplifier not connected to main unit.
 Preamplifier in IMP mode.
Q: All rejected despite raw EEG of normal size and within limits on raw EEG bar.
A: Interference by a frequency which is so high that it does not show on the raw EEG curve.
 Remedy by rearranging the electrode leads to be as close together as possible.
 Optimize electrode impedance to be as similar as possible.
 Turn out light sources and other possible emitting sources.
 Move test site to another location.
 Lowering the low pass frequency in the general setup may help, but will also influence the fre-
quency content of the waveform.
Q: Recording looks very rough as if too low resolution.
A: Input rejection and gain is set to a too high level. Lower rejection and wait to start the actual recording
until you have assured that the raw EEG is not too high – control this by looking at the raw EEG curve.
It should be possible to achieve 40µV or less.
Q: Why does the raw EEG becomes very small during recording?
A: Patient is getting more relaxed during the recording. That is good. If you think that you would benefit
from a different rejection setting, stop the recording, select the same intensity manually and start
again. After this manual intensity is recorded, the instrument will stop – then start again to complete
the automatic test protocol. The recording which was not good can be deleted.
Q: Is it possible to enter a very fast stimulus rate to check for Multiple Sclerosis?
A: Stimulus rate up to 88.8 stimuli per second is available.
Q: Threshold seems to be at a much higher stimulation level than with other equipment – why?
A: Please note that two different types of accepted calibrations for ABR units exist. One is peSPL and the
other is nHL. Only stimuli in dBnHL are comparable to normal dBHL. For click stimulus the peSPL cali-
bration is 35dB lower than the nHL calibration. So, if your instrument is calibrated to peSPL, you
should realize that for example, a 70dBpeSPL stimulus equals only about 35dBnHL. This means that if
you expect to find threshold at 20dBHL, this intensity will in peSPL be called 55dBpeSPL.
You will find the peSPL or nHL indication in the lower part of the Recording screen and Edit screen as
well as on the printout.
Q: Wave I is not easy to identify even though wave III and wave V are good
A: Wave I is typically far less dominant than wave III and wave V.
Possible Remedies:
a. Reposition the mastoid electrode to be as close as possible to the pinna and horizontally in line
with the meatus so that it is close to the cochlea/auditory nerve, where wave I is generated.
b. Change Display Gain and/or rejection level.
c. Select a higher digital low pass filter in the edit screen.
d. Decrease the stimulus rate and run the tracing again.
e. Try earlobe placement of the electrodes and/or Tiptrodes.
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