Rhythmic electrode artifact can be distinguished from an electrographic seizure by recognizing that the activity arises from one electrode derivation, with sparing of neighboring channels. High electrode impedance may result in artifactual findings ranging from isolated electrode “pops” and focal continuous slow-wave activity to rhythmic pseudo-discharges mimicking seizures ( Fig. Most electrode artifacts occur when there is relatively high impedance between the recording electrode and skin. Britton, in Aminoff's Electrodiagnosis in Clinical Neurology (Sixth Edition), 2012 Electrode Artifacts A similar artifact may occur when electrode gel connects the disk electrode and the wire lead, which are usually made of different metals. An interruption in the plating of the electrode may result in battery potentials, which can appear as bizarre, high-amplitude discharges confined to the faulty electrode. Other electrode faults may result in artifact even if the electrode-scalp interface is intact. Again, the observation that the slow activity is confined to one electrode indicates that the electrode, rather than the body, is the source of the potential. Occasionally the electrode impedances change more gradually, mimicking slow activity. If popping persists, the electrode needs to be changed.
When confronted with a popping electrode, the technician should reset the electrode and apply more gel. Pops are due to abrupt changes in impedance and usually indicate either that the electrode is not securely attached or that electrolyte gel is insufficient. They are superimposed on but do not modify ongoing recording. 12-19), usually of positive polarity, that are confined to one electrode. These are abrupt vertical transients ( Fig. Improperly applied electrodes or electrode faults may result in other sorts of artifact.Įlectrode “pops” are the most common electrode artifact. Walczak, Sudhansu Chokroverty, in Sleep Disorders Medicine (Third Edition), 2009 Aberrant Signals from Faulty Electrodes Each electrode then functions both as a PU and a CC electrode. Bioimpedance can also be measured with only two electrodes. This implies a signal transmission from the CC pair to the PU pair. Bioimpedance can be measured with four electrodes: two CC electrodes and two PU electrodes. The biopotential signal is generated by electrical activity in a body organ the source is endogenic. Negligible current flows through the two PU electrodes. The current then flows through the CC electrodes, and they are therefore polarized.Īlso, it takes two pick-up (PU) electrodes to record the biopotential difference between two body contact sites. The applied voltage can be changed so that a current flows. At a certain DC voltage, no current flows, and the electrode pair is in equilibrium. It takes two current-carrying (CC) electrodes to send an electric current through the body: a source and a sink. Sverre Grimnes, Ørjan G Martinsen, in Bioimpedance and Bioelectricity Basics (Third Edition), 2015 7.1 Electrode PairĪn electrode is a unique device, it cannot function alone.
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