Study of the rheological behaviour of human blood using a controlled stress rheometer.

The aim of this work was to investigate the rheological behaviour of human blood, in a controlled stress rheometer, using different cone-plate and parallel plate geometries. Steady-shear (flow curves and kinetics) and oscillatory (strain, frequency and time sweeps) tests were performed at 37°C. The results demonstrated that rheological data are significantly influenced by the measuring geometry and the rheological parameters obtained from rheological models must be analysed with great caution. The Cross model provided a better fit of the flow curves and the Power Law model gave a better concordance between the rheological parameters obtained with the different measuring systems. The oscillatory measurements demonstrated a linear viscoelastic behaviour below a critical frequency and the Friedrich-Braun model described well the frequency sweeps experimental data in that region. The correlation between steady-shear and oscillatory properties (Cox-Merz rule) suggests that the two methods can be complementary and may give important information on red blood cells aggregation and deformability. Results from oscillatory time sweeps confirm a blood aggregation process in two steps.