Dielectric spectroscopy of human blood.

Impedance measurement is an established technique for studying the passive electric properties of cell membranes. Dispersions can be detected by studying the electric properties (capacitance and conductance) in the radio-frequency range (kHz-mHz). The theoretical interpretation is based on the Maxwell-Wagner effect at the interface between the cytoplasm and the cell membrane. The specific electric variables of the membrane, the cytoplasm, as well as the surrounding plasma (medium) are estimated by non-linear regression fitting and appropriate equations. Using a four-electrode technique, we have measured the impedance with a commercial instrument working in the frequency range of 0.2-10 mHz interfaced to a computer. Differences were found in conductivity and capacitance of blood from 1) persons exposed to organic solvents, 2) patients with metal exposure, and 3) patients with cardiovascular disease. The effects of plasma components and haematocrit are crucial when undertaking measurements on whole blood. The results are difficult to interpret but we consider perturbations in the erythrocyte membrane to be involved. Potential clinical applications will be promoted by the development of the software.