Interacoustics Eclipse Additional Information page 228

Eclipse Additional Information
2. Additional corrections apply for some transducers when used in babies. The tiny volume of the newborn
ear canal when occluded by an insert earphone gives rise to an increase in sound level; the small skull
with unfused cranial plates leads to an increase in the effective bone conduction stimulus level. Both of
these mechanism give rise to increases in stimulus levels of clinically significant amounts (up to 20dB)
which decline with maturity. There is little data available on which to base corrections for these effects.
Maximum stimulus intensity is limited to 100dBnHL by the transducers.
This ABR unit has left the factory with nHL calibration, but it can easy be changed to peSPL values.
Cochlear Microphonics (CM): Very early electrical potential generated by the hair cells of the cochlea.
These signals are different from the other signals we measure with an ABR unit, in the fact that their gener-
ated electrical potential mimics the polarity of the stimulus. All other signals measured are nerve generated
positive electrical signals.
Condensation (polarity): The polarity of a sound stimulus indicates which direction the diaphragm of the
transducer moves. Condensation makes the diaphragm move towards the ear, producing a positive pressure
in the ear canal. Considerations of polarity are primarily important for clicks, as a click consists of an acti-
vated movement in one direction only. Waveforms based on Rarefaction stimuli and waveforms based on
Condensation stimuli have slightly different morphology due to the difference in movement of the basilar
membrane and the resulting differences in the generated electrical response. Each stimulus type performs
well for ABR recordings.
Curve: See Waveform.
Digital Filter. A frequency filtering of the EEG signal, carried out while the signal is in the digital domain. For
details see "Filter".
DPOAE: Distortion Product Otoacoustic Emission
ECochG: Electrocochleography. A recording of the very early evoked potentials like Cochlear Microphonics
and ABR Wave I (also known as the whole nerve compound action potential).
EEG: Electroencephalography. A recording of the electrical potentials generated by the brain in their raw
form. In this unit the raw EEG is displayed online. In common with other AEP systems, the term "EEG" is
used by the Eclipse to encompass all unaveraged recorded electrical activity regardless of its origin. In fact
most of what is typically seen when viewing the "EEG" is usually muscle activity. The term is therefore offi-
cially a misnomer but is one that has entered the vocabulary in this subject and is understood to mean all
electrical activity.
FFT: Fast Fourier Transform
Electrical Potentials: The difference in voltage (measured in for example µV) between two measurement
points.
Electrode: The device which, when properly applied ensures the correct electrical contact to the patient.
Several types of electrodes are available. This unit was delivered with single use types, but reusable types
are available also – these require conductive electrode gel for proper contact to the patient.
Electrode Gel: Two types of electrode paste exist: One, which rubs off the outer thin layer of skin and an-
other, which is an electrically conductive paste, used to prepare reusable electrodes. Only the first type can
be used for skin preparation (you can feel the small grains of this type of paste when rubbing it between your
fingers. The paste supplied with the unit is such type of skin preparation paste).
Electrode lead/cable: The electrical wire running from the surface electrode to the Pre Amplifier.
EP: Evoked Potentials. A general term for electrical potentials generated by stimuli like sound, light etc. AEP
is a specialized subdivision of EP.
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