Evaluation of hemostasis in flowing blood.

Hemostasis and thrombosis are now increasingly recognized as integrally related to blood rheology and blood flow. Platelets, for example, are known to access the vessel wall in ways which depend upon the small-scale motions of neighboring erythrocytes, and access one another via collisions driven by gradients in blood flow velocity. In this context, flow devices have become a subject of great interest in the clinical assessment of bleeding disorders, especially platelet function defects and von Willebrand disease. While these devices currently lack standardization and outcomes measures which establish clear clinical utility, their promise remains great, particularly in the potential to simulate the microenvironment of arteries vs. veins and in their ability to incorporate such intrinsically flow-dependent phenomena as co-localization of tissue-factor-bearing microparticles with platelets, the weakness of the GPIb-vWF bond at very high shear stresses, and even the hemostatic and antithrombotic function of vascular endothelium. In contrast, currently utilized assays are often performed under static conditions that do not involve flow and therefore are not able to simulate the microenvironment of arteries and veins.