TRIPLE-FREQUENCY METHOD FOR MEASURING BLOOD IMPEDANCE

A method was developed for simultaneously measuring plasma resistance, cell interior resistance and cell membrane capacitance of blood. A th ree-element circuit model for simulating the impedance of blood was ev aluated by comparing measured and calculated impedance frequency curve s and was found feasible. The values of the three elements of the mode l could be determined by measuring the impedance amplitudes at three d ifferent frequencies. The cell membrane capacitance (C(m)) was indepen dent of temperature in the range 25-40-degrees-C and was significantly higher for blood with ethylenediaminetetraacetic acid (EDTA) as antic oagulant than that for blood with sodium citrate and acid citrate dext rose (ACD). The C(m) value of blood from patients with high erythrocyt e sedimentation rate (ESR) was found to be significantly higher than t hat of blood from patients with low ESR. This suggests that the membra ne capacitance might be a potential parameter for clinical application s.