Qiao Z G, Mørkrid L, Vøllestad N K
Research Institute of Neuropsychiatry, Dikemark Hospital, Solberg, Norway.
Med Biol Eng Comput. 1994 Mar;32(2):161-7. doi: 10.1007/BF02518913.
The Cole-Cole equation can be used to model the electrical admittance of human skin. Using a previously published two-frequency (AC excitation) three-electrode method, the admittance locus plot (ALP) in the low-frequency region (< 1000 Hz) has been shown to be very well approximated by a straight line and can be described with frequency-independent parameters; phase angle alpha pi/2, conductance at extrapolated zero frequency G0 = 1/R0, and ion relaxation time tau. The aim of the paper is to study characteristics of alpha pi/2, G0 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 small (< 2%) even during a heavy physical-exercise period. G0 corresponds well with GDC obtained by the traditional DC method at excitations up to 200 mV (relative differences < or = 5% during baseline registration). Based on these findings, two comparatively simpler methods using only one lock-in amplifier are suggested: either measuring simultaneously with DC and at one frequency with AC excitation, or measuring at two different frequencies successively. The low-frequency part of the ALP can then be determined. G0, alpha and tau estimated by these simplified methods are in good agreement with the simultaneous two-frequency method and should therefore be suited for clinical applications.
科尔-科尔方程可用于模拟人体皮肤的电阻抗。使用先前发表的双频（交流激励）三电极法，已表明在低频区域（<1000 Hz）的导纳轨迹图（ALP）可以很好地用一条直线近似，并且可以用与频率无关的参数来描述；相位角απ/2、外推零频率下的电导G0 = 1/R0以及离子弛豫时间τ。本文的目的是研究人体手掌皮肤低频ALP中απ/2、G0和τ的特性。测量数据在个人计算机上进行离线计算。即使在剧烈体育锻炼期间，απ/2的相对变化也很小（<2%）。在高达200 mV的激励下，G0与通过传统直流方法获得的GDC非常吻合（在基线记录期间相对差异≤5%）。基于这些发现，提出了两种相对更简单的仅使用一个锁相放大器的方法：要么同时用直流和一个频率的交流激励进行测量，要么依次在两个不同频率下进行测量。然后可以确定ALP的低频部分。通过这些简化方法估计的G0、α和τ与同时双频法非常吻合，因此应该适用于临床应用。
