NONLINEAR VISCOELASTICITY AND THE THROMBELASTOGRAPH .1. STUDIES ON BOVINE PLASMA CLOTS

To study the possible role of nonlinear viscoelastic effects in the th rombelastograph (TEG), clotting of bovine plasma was studied by both t hrombelastography and with a controlled strain rheometer. Clot theolog y is dominated by elastic effects at frequencies of interest. There is a well-defined regime of linear elasticity for strains less than arou nd 2%, while al larger strains the clots show significant strain harde ning, Oscillatory shear applied during clotting has little effect on t he resulting clot provided that the strain is less than 2%, but leads to substantial weakening of clots formed at larger strains. The TEG op erates within the regime of nonlinear elasticity, significantly obscur ing the interpretation of TEG amplitude in terms of an elastic modulus . Comparing the results of standard TEG experiments with those conduct ed with a modified TEG, having no oscillation during clotting, shows t hat deformation during standard thrombelastography leads to weaker clo ts than are produced under quiescent conditions.