THE MOSAIC ELECTRICAL CHARACTERISTICS OF THE SKIN

The goals of this study are: 1) to characterize the structure of the s kin by measuring impedance variations with a suction microelectrode; 2 ) to correlate the observed impedance variations with dc current pathw ays through the skin; 3) to characterize the breakdown phenomenon. We constructed a suction microelectrode with a 200-mum internal diameter and performed several tests on two male subjects. Skin impedance measu red from different locations on the forearm and palm varied considerab ly. We found that the average skin impedance on the forearm was larger than the average impedance on the palm and that the ratio between the maximal and minimal skin impedance is larger for the forearm than for the palm. For both the forearm and the palm the magnitude and varianc e of skin impedance decrease with increasing stimulus frequency. The d ensity of low impedance points observed on the forearm and palm are co nsistent with the density of dc current pathways through the skin as i ndicated by traces left on 1-cm2 Ag electrodes when we passed dc curre nt through the skin. The ratio between the highest and lowest impedanc es decreased as temperature decreased-at low temperatures the skin dis played mostly high impedances. We were not able to break down the skin using the suction microelectrode. The tests with dry and wet electrod es suggest that breakdown is of thermal nature, and that the thermal c apacitance of the saline in the suction microelectrode prevents the te mperature of the underlying skin from increasing very rapidly. In conj unction with the larger impedance values, this would tend to increase the breakdown voltage.