EW. Influence of flow properties of blood upon viscosity-hematocrit relationships

The influence of the red cell concentration (per cent hematocrit) upon blood viscosity is well known. Some physiology texts (1) portray this relationship by means of a diagram in which rela-tive or apparent viscosity is plotted against the per cent hematocrit (Figure 1). It has been demon-strated that besides the effect of cell concentration the viscosity of blood varies both as a function of the shearing stresses developed within the fluid and the rate at which these forces are distributed be-tween the adjacent fluid elements during flow (2-4). The relationship or ratio of shear stress to the gradient of velocity, or shear rate, defines the viscosity of the fluid in the absolute dimensions of dyne-seconds-cm', or poise. In his original defi