[The present state of haemorheology: methods, findings and significance with regard to physiology and pathology of the blood circulation (author's transl)].

The role of the flow properties of blood in microcirculation dynamics, as well as the significance of microcirculatory disturbances in various pathological states are discussed. The present understanding of the factors responsible for the "anomalous" viscosity of the blood is reviewed, and the methods of measuring apparent blood viscosity are assessed. Normal, rapidly-perfused microcirculation is greatly facilitated by the unusual deformability of the red blood cell, which lowers blood viscosity. Red cell aggregation, which occurs at low flow and increases the blood viscosity, is capable of maintaining and potentiating acute and/or chronic states of hypoperfusion initiated by other haemodynamic abnormalities. While under normal cardiovascular conditions vasomotion regulates and controls peripheral blood flow, in chronic states of hypoperfusion the residual blood flow is limited by the prevailing level of apparent blood viscosity.