Passive electrical properties of RBC suspensions: changes due to distribution of relaxation times in dependence on the cell volume fraction and medium conductivity

The intra- and extracellular conductivity, kappa(a) and kappa(i) as well as the cell membrane capacitance C-m of RBC suspensions are often calculated using the Pauly and Schwan equations which neglected the parameter cu of th e empirical Cole-Cole function. However, in complex materials such as RBC s uspensions with several overlapping relaxation processes the total electric al response is characterized by a broad distribution of relaxation times yi elding an alpha > 0. The locus diagram in the conductivity-planet (kappa-pl ane) is a depressed semicircle with the center below the real axis. It is s uggested, that a characterizes both the distribution in relaxation times an d the interaction between the relaxing units. Here we focus on the influenc e of interaction on a, Therefore complex conductivity measurements were don e on RBC suspensions with the hematocrit p and the conductivity kappa of th e medium as parameter. The hematocrit was varied from 0.04 to 0.95 while th ree different media (kappa=1.447 S/m, 0.571 S/m, and 0.064 S/m) were chosen . From this we could evaluate the dependence of cu on the interactions of t he cells. The electrical parameters of the suspension were calculated by th e Pauly and Schwan equations and correlated with the hematocrit. The correc t value is obtained at low p when alpha is small (p and alpha < 0.1), becau se the Pauly and Schwan equations are derived under the presumption of low cell concentration. We compared our values with findings from cell rotation experiments. We propose an algorithm to estimate the correct passive elect rical values from measurements carried out at higher p values. (C) 1998 Els evier Science S.A. All rights reserved.