Shear dependence of the fibrin coagulation kinetics in vitro.

Fibrin thrombus formation, in vivo and in vitro, preferentially occurs in regions of retarded, recirculating flow which promote local variations of the distribution of blood components, e.g. thrombin, and shear rates. To better understand the effects of shear forces on the thrombin induced fibrin coagulation process the time course of fibrin formation in a fibrinogen/thrombin solution was studied for different shear rates gamma (0 s-1 < or = gamma < or = 500 s-1) and thrombin concentrations cthr (0.1 units/ml < or = cthr < or = 1.0 units/ml). The clotting curves at zero shear and the shear induced alterations of these curves could essentially be described in terms of a reaction kinetics defined by two rate coefficients k1, k2 which can be attributed to fibrinogen cleavage by thrombin and fibrin polymerisation, respectively. For cthr > approximately 0.5 units/ml and gamma > approximately 15 s-1 an additional mechanism, presumably fibrin breakage, had to be assumed. The rate coefficient k2 was markedly more affected by cthr and shear forces then was k1. The results fit well to the growth kinetics of fibrin thrombi formed in glass models of an arterial branching.