The Influence of Shear Rate and Red Cell Concentration on Platelet Adhesion and Thrombus Formation in Human Blood

The interaction of platelets with subendothelium requires the transport of platelets to the vicinity of the surface, as well as the basic cell-surface reaction. Exposure of subendothelium to human citrated blood flowing in an annular perfusion chamber at wall shear rates (α) of 50-10,000 sec^-1 indicates that a diffusion controlled (DC) transport regime exists below 650 sec- l in which platelet adhesion (C+S) was strongly dependent on α, and thrombus formation (T) was absent . Above 800 sec^-1, an apparently reaction controlled (RC) regime predominates in which C+S was independent of α, and T increased in both extent and size. Variation of hematocrit (H) from 0-701. in the RC regime (2600 sec^-1) lead to a steady increase of C+S with H, and an exponential increase in T as H increased from 30 to 70%. In the DC regime (200 sec^-1) virtually no thrombi were formed for all H, and C+S increased as H increased to 40%; above 40%, C+S became independent of H. Thus, at low α (venous), the platelet-subendothelial reaction is controlled primarily by the arrival rate of platelets at the surface and the red cells increase this transport for H up to 40%. At high α (microcirculatory) , the platelet-vessel wall reactivity becomes more dominant and red cells increase the ability of platelets to attach to the subendothelium.