Dynamic structure of blood flow in microvessels.

The present article summarizes the author's perennial research on the flow of red blood cells in microvessels, the major determinant of rheological properties of blood in the microcirculation. Two main patterns of blood flow structure in microvessels, in the smallest arteries and veins and in the capillaries are described. The red cell concentration (hematocrit) in the blood flowing in microvessels undergoes regular alterations with changes of blood flow rate and vessel diameter in the microvascular beds. Further, the red blood cell concentration and flow velocity gradients are found in the cross-section of microvessels that should considerably affect the blood rheological properties in the microcirculation. In addition, radial displacements and blood velocity fluctuations of red cells in the flow are discovered in the larger microvessels during ischemic decrease of blood flow rate. The main factor disturbing the normal blood flow structure, and hence the normal rheological properties of blood, is the intravascular aggregation of red blood cells, which is to be diagnosed and eliminated in patients with blood rheological disturbances.