Effects of cell adhesion and aggregation on the flow in microvessels

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Fluid-dynamic study has been performed on the effects of adhesion and cohesion of cells on the flow in microvessels. Microscopic models for blood cells have been made to analyze numerically the motion of individual blood cells in microvessels and the flow filed around them. Special emphasis was put on the adhesion of leukocytes on the venular wall and flow of red cells with high concentration which is observed in the upstream of a leukocyte in capillaries. In each case, the resistance to flow has been calculated. It was found that, in the former case, the flow resistance strongly depends on the ratio of cell height to vessel diameter and the number of adherent cells, and its increase is more pronounced in venules with smaller diameters. In the latter case, our model simulation predicted an increase in flow resistance which accounts for an in vivo observation in skeletal muscle microcirculation. Based on this result, a mechanism was proposed whereby the interaction between a leukocyte and red cells in capillaries serves to elevate flow resistance in the capillary network. When a leukocyte is (1)freely floating in microvessels, (2)adherent to the venular wall, and (3)rolling along the wall, the shear stresses acting on the membrane of the leukocyte and vascular endothelial cells exerted by the fluid flow were computed. The results indicate that the shear stress distributions on the leukocyte membrane are nonuniform in all cases. The magnitudes of the fluid stresses in cases (2) and (3) are about ten times larger than in case (1), while their high temporal gradient is significant in case (1).