Quantitative evaluation of flow dynamics of erythrocytes in microvessels: influence of erythrocyte aggregation.

Effects of erythrocyte aggregation on the flow dynamics of erythrocytes in microvessels were examined quantitatively by perfusing human erythrocytes suspended in isotonic medium containing various concentrations of dextran (70,400 avg mol wt, Dx-70) into a part of the microvascular bed isolated from rabbit mesentery. Thickness of the marginal cell-free layer was measured with an image analyzer, total flow resistance was determined on the basis of the perfusion pressure-volume flow relationship, and homogeneity of erythrocyte flow was evaluated by the power spectrum obtained by the fast Fourier transform of the light intensity change monitored on single microvessels. With increasing dextran concentration, suspension viscosity of erythrocytes at high shear rates increased linearly and thickness of the cell-free layer increased in a sigmoidal fashion. Flow resistance increased relatively little over the range of dextran concentrations in which the cell-free layer increased most rapidly. Furthermore, the flow pattern of erythrocytes in microvessels became inhomogeneous. In conclusion, the present study shows that Dx-70-induced erythrocyte aggregation results in increased flow resistance in the circulatory system, even through the widening of the cell-free layer tends to reduce the resistance and also results in inhomogeneous flow of erythrocytes in microvessels.