Effect of Velocity Gradient on the Clotting Time of Blood and on the Consistency of Clots Formed in Vitro

Abstract

Clotting times of human blood and rheology of blood clots have been determined by means of a cone-in-cone viscometer, a ring-in-ring adapter, and a variable-frequency thromboviscometer. The last represents a variable frequency version of the thrombelastograph. The results of clotting time tests on blood samples from 118 donors indicate clearly that clotting time is a function of the velocity gradient at which clotting takes place. Clotting time decreases as the velocity gradient increases. Consistency of blood coagula depends on the velocity gradient at which coagula are formed. Consistency, or viscosity, of coagula decreases when the velocity gradient increases. While the viscosity of clots formed at low rates of shear is of the order of 100 poises, coagula formed at intermediate rates of shear exhibit viscosity of a few decipoises. Viscosity of blood is not significantly altered if coagulation takes place at rates of shear near 400 sec -1 .