Interacoustics Eclipse Additional Information page 215

Eclipse Additional Information
Q: Sometimes it just seems to block during testing.
A: If the patient is restless or tense, you will run into full rejection. This will be observed as the raw EEG
curve turns yellow or red. Remedy by having the patient relax, providing EEG levels below the rejec-
tion threshold.
Q: What delay in response times should be expected when using the inserts?
(published norm data is often based on headphone use)
A: We have compensated for the delay, so 0 on the time scale equals headphone presentation.
Q: There seems to be too much noise – the EEG cannot come down to 20µV.
A: Grounding through the mains connection is vital as covered elsewhere. Also you may try to connect a
wire between the ground (chassis) of the EP system and the metal parts of the patient's bed or chair.
This connection is available on the EP system through the finger screw located next to the power cord
connection.
Q: Waveforms are of very poor quality.
A: Check that the following is not in place:
 Instrument not properly grounded through the mains supply.
 Electrodes not properly mounted.
 Electrode Impedance too high – check impedance.
 Click Stimulation too low (90dBpeSPL = 55dBnHL)
 Earphones not correctly mounted or connected.
 Pre Amplifier still set to Impedance Check (total rejection).
 Electrode leads broken – check impedance.
 Patient not relaxed.
 Patient not responding normally.
 Also remember that some patients do not display perfect textbook curves.
Q: Can I use notch filtering?
A: No, as the notch filtering has the consequence of waveform latency shift (also amplitude is reduced),
the notch filtering cannot be advised.
To reduce the latency shift effect, often notch filters have a very small attention, but this also means
that the effect of reducing the 50 or 60Hz component is not efficient.
Q: Should I change the filter from 33-100 Instead?
A: Only as a last resource, this will reduce the amplitude of the waveform response, but keep the latency
intact. The common mode rejection ratio (CMRR) of the preamplifer is designed to deal with common
signals and attenuate these low frequencies up to 140dB. You can ensure best CMRR by:
1. Low and balanced electrode impedance.
2. Place the ground electrode closest to the noise source on the test subject. This will to drive the
noise into the preamplifer improving the reduction of the noise artefact.
3. Ensure a dedicated ground is connected to the Eclipse.
4. Ensure that patient bed/chair is connected to ground.
Q: Raw EEG very small before recording is started.
A: Rejection level default setting 20µV is suitable for most ABR applications – perhaps higher with
Bayesian weighting). – remedy by changing rejection level on the arrows by the raw EEG curve.
Electrode leads are short circuited. Make sure that cables are not defect and the surface electrodes
are not overlapping.
Q: The raw EEG is very large.
A: Raw EEG sensitivity is set to a too ambitious level – e.g. 5µ Volts. Remedy by restarting the test by
adjusting the rejection level of the raw EEG with the corresponding arrows.
 One or more electrode not properly connected.
 Impedance too high or uneven between electrodes.
 Patient not relaxed.
 Electrode lead broken.
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