Dielectric spectroscopy of blood

An experimental investigation of complex dielectric spectra of human blood in the frequency range 30 Hz-30 MHz has been carried out for various blood cell concentrations, temperature and environment. Electrode impedances and other distorting effects have been excluded. The average values of the dielectric constant (DC) P. and conductivity gamma of normal heparinized blood for the lowest (epsilon(0), gamma(0)) and the highest frequencies (epsilon(infinity), gamma(infinity)) are: epsilon(0) = 7500; gamma(0) = 4.9 mS/cm; epsilon(infinity) = 160; 9 mS/cm. The characteristic relaxation time r = 0.265 mus with a Cole-Cole distribution around it; only beta-dispersion is observed in normal blood. The DC of resting blood is considerably larger than that of stirred blood; this is associated with the formation of small aggregates of blood cells. The temperature dependence of the static DC shows a maximum at the temperature 37 degreesC. According to Fricke-Pauly-Schwan theory the membrane capacity C,,, of stirred blood at normal concentration is 0.8 muF/cm(2) and depends strongly oil concentration of cells and stirring. Damaged and aged cells manifest, in addition to beta-dispersion, a low-frequency alpha-dispersion, which call be explained as a result of the formation of large aggregates of cells. (C) 2002 Elsevier Science B.V. All rights reserved.