Blood rheological properties and methods of their measurement

Abstract

From the physical point of view, blood is a multi-phase and multi-component system; plasma is the dispersion medium and the morphotic elements are the dispersed phase. Flow rate analysis is essential to determine the correct rheological properties of blood. Slow blood flow can lead to increased erythrocyte aggregation, which is due to fibrinogen and globulins. The deformability of red blood cells is also important, especially during flow through the capillaries, where they must adapt to the smaller diameter of the vessels. Viscosity is defined as the internal resistance to flow; if we consider blood as a component of two parallel layers, then viscosity is described by the friction of two adjacent layers. The liquid layers move at different velocities parallel to each other, and a velocity gradient is created. To create it, a force is needed to move the layers, which is referred to as shear stress. Erythrocyte aggregates are observed physiologically as well as in the course of some diseases such as ischemic heart disease, myocardial infarction and atherosclerosis. There are two types of factors inducing the formation of aggregates: the external factors include the plasma protein concentration, hematocrit and shear forces; the internal factors are the shape and deformability of the erythrocytes in addition to the properties of the cell membrane. Also in hyperfibrinogenemia, erythrocyte aggregation, plasma viscosity and microvascular resistance increase. The laser-assisted optical rotational cell analyzer (LORCA) is used to test the deformability and aggregation of erythrocytes. It combines the techniques of syllectometry with ektacytometry. The formation of a three-dimensional structure of red blood cells has a significant impact on the measurement of blood viscosity and low shear rate blood flow.

Keywords

• rheology
• blood viscosity
• erythrocyte aggregation
• erythrocyte deformability