Rheological hysteresis of blood at low shear rate 1

A Couette type servo-controlled microviscometer associated with a low frequency generator modulating the rotational speed of the viscometer outer cylinder has been used to plot the rheological hysteresis curves of blood. It has been shown that the shape of these curves largely depends on the values of the parameters α and t_m characterizing the linear variation of the rate of shear with time: γ ˙ = α t for 0 < t < t m and γ ˙ = α ( 2 t m − t ) for t m < t < 2 t m . Two sets of α and t_m have been selected in order to obtain rheograms showing preferentially the viscoelastic or the thixotropic behaviour of blood. This technic is used to compare normal human bloods with bloods submitted to various physical or chemical treatments, or with different pathological bloods. Some interpretations are proposed from considerations on changes in the deformability or aggregability of blood cells.