Blood rheology: effect of fibrinogen deduced by addition.

where rv is the yield stress and b is a constant. For this reason, data in the low shear region are conveniently plotted with the ordinate scale proportional to the square root of shear stress and the abscissa scale proportional to the square root of shear rate. Nearly straight lines result, the ordinate intercept of which is the yield stress. The yield stress is that value of shear stress below which no flow is possible. These rheological relationships are the result of a reversible "structuring" of blood that occurs between red cells in the presence of fibrinogen. Although plasma proteins other than fibrinogen may play a synergistic role in the presence of fibrinogen, they have no effect in the absence of fibrinogen. Suspensions of red cells in physiological saline solutions of the plasma proteins other than fibrinogen show almost the same rheological characteristics as suspensions of red cells in plain physiological saline; they are almost Newtonian and totally lack yield stress. As shown elsewhere, the yield stress at constant fibrinogen concentration depends strongly on the