On biomedical electrode technology : with special reference to long-term properties and movement-induced noise in surface electrodes

Abstract: The aim of the present investigation was to improve the quality of surface electrode measurements. Long-term properties of commercially available ECG-electrodes were studied by investigating polarization potentials, electrode impedance, adhesion and skin reactions during a period of 7 days. The most stable polarization potentials were obtained for Ag/AgC1-electrodes and stable electrode impedance were obtained for disposable electrodes with stable adhesion and equipped with an electrode capsule. Unchanged adhesion and mechanical strength were shown by disposable electrodes with large self-adhesive collars.Movement-induced potentials of streaming potential type were studied in various electrode configurations. The geometric design of the electrode was important for reduction of noise generated by the movement of gel. Potential and impedance variations were measured for electrode movements in electrolytes relative to the skin. The impedance variations were small and streaming potentials with a magnitude of up to 10μV were recorded. The deformation potentials generated in the skin dominate the disturbance pattern in surface electrode recordings. Potential and impedance variations studied with varying mechanical stress upon skin showed that the impedance variations did not bring about the potential variations. The size of potential variations in skin and related mechanical stress possess a non-linear relationship which varies between individuals. A non-linear character of the time sequence of stretch potentials was found.The spread of deformation potentials was studied in the skin area around and beneath surface electrodes. When stretching a rectangular skin zone between two plates fixed to the skin the highest potentials were obtained in the zone. The magnitude of the potentials decreased with the distance to the zone. Stretch potentials could be reduced but not geometrically limited by fixing the skin to a rigid electrode collar. The potential spread is a consequence of successively decreasing deformation.