CHARACTERISTICS OF PHASE-ANGLE, EXTRAPOLATED CONDUCTANCE AND ION RELAXATION-TIME IN THE LOW-FREQUENCY ADMITTANCE LOCUS PLOT OF HUMAN PALMARSKIN

The Cole-Cole equation can be used to model the electrical admittance of human skin. Using a previously published two-frequency (AC excitati on) three-electrode method, the admittance locus plot (ALP) in the low -frequency region (<1000 Hz) has been shown to be very well approximat ed by a straight line and can be described with frequency-independent parameters; phase angle alpha pi/2, conductance at extrapolated zero f requency G(0) = 1/R(0), and ion relaxation time tau. The aim of the pa per is to study characteristics of alpha pi/2, G(0) and tau in the low -frequency ALP of human palmar skin. The measured data are calculated off-line on a personal computer. Relative changes in alpha pi/2 are sm all (<2%) even during a heavy physical-exercise period. G(0) correspon ds well with G(DC) obtained by the tradition DC method at excitations up to 200 mV (relative differences less than or equal to 5% during bas eline registration). Based on these findings, two comparatively simple r methods using only one lock-in amplifier are suggested: either measu ring simultaneously with DC and at one frequency with AC excitation or measuring at two different frequencies successively. The low-frequenc y part of the ALP can then be determined. G(0), alpha and tau estimate d by these simplified methods are in good agreement with the simultane ous two-frequency method and should therefore be suited for clinical a pplications.