Shear rate-dependent impairment of thrombus growth on collagen in nonanticoagulated blood from patients with von Willebrand disease and hemophilia A.

Thrombus formation on collagen fibrils was quantified at venous (100/s) and arterial (650/s and 2,600/s) wall shear rates in blood from patients with various subtypes of von Willebrand disease (vWD) and with hemophilia A (HA). Nonanticoagulated blood was drawn directly from an antecubital vein over purified type III collagen fibrils exposed in parallel-plate perfusion chambers. Blood-collagen interactions were differentiated and quantified by morphometry as platelet adhesion, thrombus height, thrombus volume, and deposition of fibrin strands. Sixteen patients with vWD, including four type III, six type I, four type IIA, and two type IIB, were compared with 26 normal subjects and nine patients with HA, including six severe HA and three mild HA. Platelet adhesion and thrombus formation at 2,600/s were significantly decreased in blood from patients with vWD type III, IIA, and IIB, but not in blood from patients with type I and in HA. The abnormal thrombus formation was apparently not related to the decreased levels of factor VIII (F.VIII), because thrombus height and volume were normal in severe and mild HA. Thrombus formation at 650/s was also significantly decreased in patients with vWD type III, IIA, and IIB and slightly reduced in type I. Significant reduction in thrombus volume and height was also observed in blood from patients with severe HA, but not in mild HA. Thrombus dimensions were not affected at 100/s in the vWD subtypes. However, significantly decreased thrombus height and virtually absent fibrin deposition were observed in blood from patients with severe HA. Apparently, F.VIII supports thrombus formation at low and intermediate shear conditions, presumably through the generation of thrombin. In contrast, von Willebrand factor (vWF) mediates not only platelet adhesion, but also thrombus formation at intermediate and high shear rates. Thus, the relative contribution of coagulation (F.VIII) and platelet function (vWF) in thrombus formation appears to be shear rate dependent, but having optimal effects at different shear conditions.