INVESTIGATION ON ETHANOL AND PROPYLENE GLYCOL AS ENHANCERS FOR SKIN-ELECTRODE CONDUCTIVITY IN BIOELECTRICAL POTENTIAL MEASUREMENT

In bioelectrical potential measurement with restricted skin-electrode contact area, such as in dense array EEG measurement where the electrolyte bridging effect1 is a major concern for signal reliability, an enhanced electrolyte solution is required for the skin-electrode impedance to reach the sufficiently low level within the minimum time interval. In this study, an electrolyte gel with its skin permeation ability enhanced by ethanol or propylene glycol has been investigated. The standard skin-electrode impedance measurement was carried out on the forehead in an area of 6 mm in diameter using standard Ag / AgCl EEG electrodes. The gel solutions with 0%, 7%, 18% and 28% of enhancers by volume are compared. The results show that both ethanol and propylene glycol reduce the permeation barrier of the stratum corneum so that ions in the electrolyte gel can penetrate more readily into the skin, enhancing the skin-electrode conductivity in reaching the steady value at a faster rate. It was further found that for the gel with higher percentage of ethanol, lower minimum skin-electrode impedance value was obtained. However, as the percentage of propylene glycol increased, it fails to attain low steady impedance values in the skin-electrode impedance measurements.

Body Surface Laplacian Mapping of Bioelectrical Activity

A method is described to process and interpret multi-channel bioelectrical signals. The bioelectrical signals were recorded noninvasively over the body surface of human subjects at 120 sites. The body surface Laplacian maps were then constructed from the multi-channel bioelectrical potential measurement. The method was evaluated by means of computer simulations, and applied to imaging cardiac electrical activity. The present investigation suggests body surface Laplacian mapping provides an important means in interpreting bioelectrical signals.