Red Cell Deformability and its Relevance to Blood Flow

Abstract

The resistance to blood flow is a function of the rheological properties of blood as well as the geometric features of blood vessels. While circulatory investigations generally aim at studying the functions of the heart and blood vessels, there is an increasing realization that blood rheology can also play a significant role in circulatory regulation in health and disease (10, 11). The principal factors determining blood viscosity are hematocrit, plasma viscos­ ity, cell aggregation, and cell deformability (8). This review focuses on the role of the deformability of the red blood cell (RBC) in circulatory regulation under physiological and pathophysiological conditions. 1 Deformability is a relatively general term that describes the ability of a body (RBCs in this case) to change its shape in response to a deforming force. RBC deformation (or strain) can involve a change in cell curvature, a uniaxial deformation, or area expansion (3, 33). The deforming stress (force per unit area) is usually applied from outside the cell, e.g. by fluid shear stress or local membrane aspiration, but it can also originate from within the cell, e.g. RBC swelling in hypotonic medium or fiber formation in deoxygenated sickle cells. The extent, rate, and mode of deformation depend on the magnitude, rate, and direction of the stress. Therefore, the stress-strain (and stress-strain rate) relationships are complex and cannot be described by a single deformability parameter.