Non-Newtonian Viscosity and Dynamic Viscoelasticity of Blood during Coagulation

Abstract

The steady flow viscosity of blood and plasma during the early stage of coagulation was measured by a coaxial cylindrical viscometer in a range of shear rate from 2 to 100sec-1. The relation between stress and shear rate observed for clotting blood was well represented by Casson's equation. The plastic viscosity and yield value increased as the coagulation proceeded appreciably.To measure the dynamic viscoelastic moduli, the blood or plasma was poured into a gap between the two coaxial cylinders, which were connected to two strain gauges respectively. The outer cylinder was vertically oscillated at a frequency of 10c/s and with an amplitude of 60 microns to cause the shear strain to the sample. The alternating stress given to the inner cylinder due to viscoelastic properties of the sample was detected by the strain gauge and dissolved into two components, one with the same phase with strain and the other being 90 degree out of phase with strain. The former gave dynamic elastic modulus E′ and the latter dynamic loss modulus E″.In a few minutes after adding coagulant to the sample, E′ first began to increase, followed by the rise of E′. The earlier increase of E″ would indicate the onset of polymerization of fibrinogen into fibrin. Rapid increase of both E′ and E″ in succession was observed, which suggested the formation of networks of fibrin fibers. The time required for E′ and E″ to reach the saturated values was several hours for whole blood and less than 1 hour for plasma. When the plasma was diluted with water, keeping the hematocrit unchanged, the saturated values of E′ and E″ decreased. The presence of blood cells largely increased the saturated values of E′ and E″ in whole blood.