ERYTHROCYTE FLOW AND ELASTICITY OF MICROVESSELS EVALUATED BY MARGINALCELL-FREE LAYER AND FLOW RESISTANCE

Flow dynamics of human erythrocytes was compared in elastic (E) and ha rdened (H) microvessels with inner diameters of 10-40 mu m. The thickn ess of the marginal cell-free layer and the overall flow resistance we re measured with a vascular bed isolated from rabbit mesentery (E vasc ular bed) as well as with a 4% paraformaldehyde-fixed bed (H vascular bed). 1) In both E and H microvessels, the thickness of the cell-free layer increased with increasing inner diameter of the microvessels and with decreasing hematocrit accompanied by an overall decrease in the flow resistance. The hematocrit-dependent change of the cell-free laye r thickness was greater in the E microvessels than in the H microvesse ls. The flow resistance was always greater in the H vascular beds than in the E vascular beds. 2) With decreasing erythrocyte deformability induced by treatment with 2 mM diazenedicarboxylic acid bis(N,N-dimeth ylamide), the thickness of the cell-free layer decreased at a low hema tocrit in the E microvessels at a high hematocrit in the H microvessel s, although the flow resistance increased in both vascular beds. 3) De xtran of 70,400 average molecular weight accelerated the formation of the cell-free layer by inducing erythrocyte aggregation. A drastic inc rease in the cell-free layer thickness at 2-4 g/dl of dextran in the E microvessels and at 1-2 g/dl of dextran in the H microvessels was acc ompanied by a significantly lower increase in the flow resistance. Thi s study concludes that the elasticity of microvessels may play an impo rtant role for reducing the overall flow resistance of a vascular bed, which is modulated by the marginal cell-free layer, itself a function of the rheological properties of the erythrocytes.