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 three-element circuit model for simulating the impedance of blood was evaluated by comparing measured and calculated impedance frequency curves and was found feasible. The values of the three elements of the model could be determined by measuring the impedance amplitudes at three different frequencies. The cell membrane capacitance (Cm) was independent of temperature in the range 25-40 degrees C and was significantly higher for blood with ethylenediaminetetraacetic acid (EDTA) as anticoagulant than that for blood with sodium citrate and acid citrate dextrose (ACD). The Cm value of blood from patients with high erythrocyte sedimentation rate (ESR) was found to be significantly higher than that of blood from patients with low ESR. This suggests that the membrane capacitance might be a potential parameter for clinical applications.