Effects of cell adhesion and aggregation on the flow in microvessels

本文对细胞的黏附和内聚对微血管内流动的影响进行了流体动力学研究。为了数值分析单个血细胞在微血管中的运动及其周围的流场，建立了血细胞的微观模型。特别强调了白细胞在静脉壁上的粘附和高浓度红细胞的流动，这是在毛细血管中白细胞的上游观察到的。在每种情况下，都计算了流动阻力。结果发现，在前者情况下，流动阻力与细胞高度与血管直径之比和贴壁细胞数量密切相关，且在直径较小的小静脉中流动阻力的增加更为明显。在后一种情况下，我们的模型模拟预测了流动阻力的增加，这说明了骨骼肌微循环的体内观察。基于这一结果，提出了一种机制，即白细胞和毛细血管中的红细胞之间的相互作用有助于提高毛细血管网络中的流动阻力。当白细胞(1)在微血管中自由漂浮，(2)粘附在静脉壁上，(3)沿着壁上滚动时，计算流体流动对白细胞和血管内皮细胞膜施加的剪切应力。结果表明，在所有情况下，白细胞膜上的剪切应力分布是不均匀的。在情形(2)和(3)中流体应力的大小大约是情形(1)的10倍，而在情形(1)中它们的高时间梯度是显著的。

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).