Electrical impedance and haematocrit of human blood with various anticoagulants.

The relationship between the electrical impedance parameters and the haematocrit of normal human blood has been determined at 37 degrees C in the haematocrit range of 20-60% for four types of anticoagulant: ACD, EDTA, sodium heparin and buffered sodium citrate. For plasma resistance Rp and interior resistance R(i), the measured data could be fitted by both the exponential expression and the Maxwell-Fricke expressions, Rp = a/(1-h) + b and R(i) = a/h + b, where a and b are constants and h is the haematocrit expressed as a decimal. The membrane capacitance Cm was found to be directly proportional to the haematocrit and could be normalized to 100% haematocrit by the Fricke formula, C100 = C(m)/(1-rho p/Rp), where rho p is the resistivity of plasma. Observed differences for Rp and C(m) among samples with various anticoagulants indicate that the type of anticoagulant influences the electrical properties of the red cells and the plasma.