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) ε and conductivity γ of normal heparinized blood for the lowest (ε0,γ0) and the highest frequencies (ε∞,γ∞) are: ε0=7500; γ0=4.9 mS/cm; ε∞=160; γ∞=9 mS/cm. The characteristic relaxation time τ=0.265 μs 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 °C. According to Fricke–Pauly–Schwan theory the membrane capacity Cm of stirred blood at normal concentration is 0.8 μF/cm2 and depends strongly on concentration of cells and stirring. Damaged and aged cells manifest, in addition to beta-dispersion, a low-frequency alpha-dispersion, which can be explained as a result of the formation of large aggregates of cells.