Complex Microvascular Effects Involving Plasma and Red Cell Movement in Brain Following Alterations of Viscosity

Abstract

The term “viscosity,” when applied to blood, always represents an awkward adaptation to physiology of a concept which in its strict sense can only apply to a Newtonian fluid. The adaptation is awkward because blood is a suspension, not a fluid, and its behavior is not Newtonian. This may provide a partial explanation for the tendency of many workers to accept as understandable, data in which alterations in blood viscosity were purported to have little or no effect on the circulation. Generally speaking, the changes in viscosity were measured on a sample of blood, in vitro, and these changes were related to alterations in blood flow. Much of this literature was reviewed by me in an earlier article [3]. In general, when in vitro viscosity levels are changed and it is concluded that there is little or no effect on circulation, what is really meant is that there has been little change in flow. In fact, the circulatory system has been greatly affected. For example, the diameter of the resistance vessels has been altered to compensate for the altered viscosity, thus maintaining a constant or near constant flow [1, 2].