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 variat ions of the distribution of blood components, e. g. thrombin, and shea r rates. To better understand the effects of shear forces on the throm bin induced fibrin coagulation process the time course of fibrin forma tion in a fibrinogen/thrombin solution was studied for different shear rates gamma (0 s(-1) less than or equal to gamma less than or equal t o 500 s(-1)) and thrombin concentrations c(thr) (0.1 units/ml less tha n or equal to c(thr)1.0 units/ml). The clotting curves at zero shear a nd the shear induced alterations of these curves could essentially be described in terms of a reaction kinetics defined by two rate coeffici ents k(1), k(2) which can be attributed to fibrinogen cleavage by thro mbin and fibrin polymerisation, respectively. For c(thr)>approximate t o 0.5 units/ml and gamma>approximate to 15s(-1) an additional mechanis m, presumably fibrin breakage, had to be assumed. The rate coefficient k(2) was markedly more affected by c(thr) and shear forces then was k (1). The results fit well to the growth kinetics of fibrin thrombi for med in glas models of an arterial branching.