Physical movement of electrodes or their leads and variation of pressure on an electrode may cause artefactual potentials. The leads may move in an external electrostatic or magnetic field, movement of electrode jelly may cause fluctuation of electrolyte charge under the electrodes, compression of scalp blood vessels altering local blood flow may cause local potential variations.
This is common in intensive care monitoring. Pulsation of ventilator tubing causes small movements of the head and body causing regular movements of the electrode leads or variations of pressure on an electrode. Some repositioning of head support or supporting the tubing may reduce this mechanical artefact.
Vibration of the body with the heart beat. Normally only visible or significant on low amplitude recordings. This can be difficult to avoid.
Pulsation of a blood vessel in the vicinity of an electrode. Normally cured by moving the electrode to a new site.
Contractions in response to a stimulus such as a galvanic "train of four" used for assessment of neuromuscular block. The cause
is usually easily identified. Some repositioning of head support may reduce this mechanical artefact.
