Background: Colloidal fluids, e.g. hydroxyethyl starch (HAES), used as blood plasma substitutes during acute controlled normovolemic hemodilution may cause erythrocyte aggregation. The aim of the presented study was to assess the degree and rate of erythrocyte aggregation in the media containing different concentrations of HAES.
Material/Methods: The experiments were carried out on heparinized venous blood and on erythrocyte suspension in 0.9% NaCl.
Results: Under stationary conditions, an increase of blood and erythrocyte suspension relative electric permitivity (ε), with an increase of HAES concentration in the sample, was observed after HAES supplementation. Sample flow through a measuring chamber resulted in decrease of the εL value (determined for 100 kHz). Stopping the flow led to non-linear increase of εL values in the function of time, where two components – characterized by rapid and slow variability, respectively, could be distinguished. The increase was characterized by τ1 and τ2 relaxation times, which can be related respectively to the process of erythrocyte rouleaux formation and to the formation of 3-D network aggregates.
Conclusions: 1) The values of εL are differentiated by the degree of erythrocyte aggregation due to the presence of HAES, both in whole blood and in erythrocyte suspension in 0.9% NaCl solution,2) The degree of erythrocyte disaggregation due to flow increases with the increase of flow intensity and correlates with decreasing εL value, 3) τ1 and τ2, which characterize the kinetics of erythrocyte aggregation, indicate a difference between aggregation processes taking place in whole blood and after hemodilution with HAES.

Keywords: dielectric spectroscopy, Erythrocyte Aggregation, Hemodilution, hydroxyethyl starch (HAES)