The rheology of red blood cell aggregates

Abstract

The aggregation and disaggregation of red blood cells is a critical variable in the rheology of blood in both physiologic and pathologic conditions. A direct visualizing viscometer (Rheoscope) was used to analyze the formation, dispersion, and flow behavior of aggregates under quantified flow conditions. Pathologic aggregates differed from normals in that they were considerably more resistant to shear and settled more rapidly. Red cells from acutely ill patients formed typical aggregates in serum indicating that serum proteins rather than fibrinogen alone are involved in the development of aggregates in pathological conditions. The elasticity and flow behavior of the aggregates were altered by osmotic swelling and crenation of the cells, which had profound effects upon aggregate formation and deformation. Their resistance to shear was not affected. These studies indicate that while red cell aggregation is a physiologic process, there are qualitative as well as quantitative differences between normal and pathologic aggregation, and that these differences are related to changes in red cell size and shape, plasma proteins, and the ambient flow (shear) forces within the circulation.