The Elastic Constant of Coagulative Viscoelastometry

Abstract

Clot strength is of utmost clinical significance. The elastic constant of the forming clot is a surrogate of its strength. The elastometric assessment of the forming clot, known as thromboelastography, is therefore of utmost clinical importance. Thromboelastography using a rotational viscoelastometer requires a geometric model to couple the shear deformation of a forming blood clot to its viscoelastic properties. Hartert’s original model idealized the complex geometry of the clot as a single cuboid and predicted a maximal effective shear modulus G_max=5000 dyn/cm². Hochleitner et al. recently reviewed this decades-old model, with the aim to refine it by reducing geometric simplifications that made the model more tractable. Hochleitner’s revised model uncouples annular segments and idealizes them as cuboids, thereby obtaining a maximal effective shear modulus of G_max=4466 dyn/cm². Hochleitner’s idealizations, while more accurate that Hartert’s, still produces error of at least 52%. Using the actual formula for annular shear from an applied torque, as derived by Ramberg and Miller, obviates several geometric simplifications assumed for analytical tractability and produces an elastic constant of G=2930 dyn/cm². The clinical importance of precise determination of the formula for transforming clot amplitude to clot strength is underscored by the nonlinear relationship between elastometric amplitude and elastic constant, as the systematic error cannot be linearly rescaled. Thus, clot strength in several clinical scenarios should be based on clot strength as opposed to clot amplitude.