The review of contemporary ideas about the influence of flow rate on blood clotting

Normal blood clotting is vitally important for mammals. The diffusion-convection transfer of clotting factors plays a key role in blood clot formation. Since the shear rates of blood flow are very high (up to 7000 s −1 ), clot formation critically depends on the flow rate. The methods of study of the flow effect on clotting are indirect and the processes are rather complex; therefore, mathematical models of this process are significant for interpretation of results and understanding of the mechanisms. The review expounds the main experimental data on the effect of flow on the blood clotting cascade, some hypotheses and mathematical models explaining different regimes of the functioning of this system. The review is focused on specific problems encountered by researchers in this field. Some of the experimental works have shown that flow decreases the size of the formed fibrin clot and that the dependence of clot formation period on the flow shear rate is a threshold function. However, there are also experimental evidence that the flow can increase production of clotting factors (factor Xa), which must be expressed in the procoagulant action of the flow. Mathematical models of different aspects of clotting give no unified predictions either. Nevertheless, the combined analysis of results of detailed modeling and experiments, in our opinion, may result in understanding of the mechanisms, which determine the behavior of clotting in a flow.