Electrical time constants of erythrocytes for confocal and uniform thickness membrane

Abstract

The physical properties of tissues are of practical interest in medical engineering and various fields of medicine. In this study, the electrical time constants of living cells, especially erythrocytes, are discussed. β dispersion is often called as structural relaxation caused by cellular structure of tissues. The shape of cells, the membrane thickness of cells, the conductivity of intracellular fluid and the orientation of the cells affect the time constant of β dispersion. Therefore, we can get a lot of information such as intra- and extra-cellular volumes from β dispersion phenomenon. [1][2][3][4][8][11]. The electrical properties of blood can be analytically calculated by Fricke equation under some assumptions [9]. The most important assumption is that the shape of erythrocyte in blood approximated to the confocal ellipsoidal spheroid (shown in Fig.1). And all erythrocytes orient themselves so as to one of three -rectangular axis is parallel to the electrical field. This model has a single time constant, although the time constant of a real erythrocyte with constant membrane thickness must be distributed. As a result, the difference exists between the admittance locus analytically calculated from Fricke's model and the experimental results obtained from blood. In this study, comparison of the results analytically calculated by Fricke's equation and the results numerically calculated by boundary element method for the model with the uniform membrane thickness were compared. From these results, the error of Fricke's results can be estimated. These results were expected to improve the electrical bio-impedance method. © Springer-Verlag 2007.