Non-newtonian Rheology of Human Blood--effect of Fibrinogen Deduced by "subtraction".

• Blood has been recognized as a non-Newtonian fluid for many years. Only recently' have the rheological properties of blood been studied under shear rates near zero flow. These studies have suggested that the viscosity of blood increases indefinitely as the shear rate approaches zero. The problem of blood rheology under very low shear rates seemed to us worthy of further investigation, because in various vessels, or sequences of vessels, in the human microcirculation it is possible that, from time to time, blood flow may temporarily cease. The cinephotomicrographic studies of Fulton and co-workers on the cheek pouch of the hamster demonstrate that intermittent cessation of flow of blood does in fact occur from time to time in healthy animals. If flow has completely ceased within a given sequence of vessels of the microeirculation, it is the rheological character of blood at zero shear rate that is relevant to the dynamics of re-starting flow. Gabelnick was the first to compare the rheological characteristics of human blood at shear rates near zero flow with the characteristics of a suspension of red cells in Ringer's solution, at equivalent hematocrit levels and under equivalent shear rates. Gabelnick shoAved that the suspension of red cells in Ringer's solution "was lower in viscosity by two orders of magnitude and more nearly Newtonian than blood. He concluded that