Micromechanical methods to determine haemorheological parameters.

SUMMARI The fluidity of blood in microcirculation is mainly determined by the micromechanical properties of its corpuscular components and its fluid, the plasma. Disorders in their rheological abilities lead to diminished perfusion of the microcir culation and cause a decrease in its nutritive function. Numerous measuring systems have been developed for diagnosing changed flow properties and especially for detecting the responsible rheological parameters. An essential condition is the reliability and reproducibility of each method. The viscosity or fluidity of blood is described by the law of HAGEN-POISEUILLE: ~ blood = ~Pj X blood The responsible microrheological parameter and some of the most suitable methods for determination as follows: 1. Hematocrit 2. Temperature 3. Plasma viscosity (capillary viscometer) 3. Platelet aggregation 4. Leucozyte flexibility 5. Erythrocyte deformability (filtration systems, e.g.: Filtrometer MF 4, Single Erythrocyte Rigidometer and 6. Erythrocyte aggregation (Miniaggregometer, rheoscope). Additionally it is necessary to get information about some hematological and biochemical parameters of the blood, e.g.: plasma proteins, pH-values, osmolarity, blood gases and electrolytes. All methods should be performed under defined conditions to achieve highly reproducible and reliable results. For a long time the flow behavior of the formed elements of the blood has frequently been neglected in respect to cardiovascular control of healthy and diseased. Blood perfusion in the arteries down to the metarterioles and in the venous system is mainly regu lated by the action of the driving pressure (heart function) and the smooth muscles of the vessel wall. But there is no explanation by the same mechanism for the arterial and venous capillaries, which diverge as thin-walled, nonmuscular channels. While, previously, only diameter changes and pressure abnormalities were considered we now have to accept that in the mammalian circulatory and res piratory system, not only the transport of the blood in arteries and veins but even more so the distribution of the blood into, and its passage through the terminal ramification of the vasculature is greatly influenced by the rheological behavior of the blood cells, primarily the erythrocytes, but also the granulocytes.' The exceptional fluidity of the red blood cells (RBC) is demons trated on Fig. I. It shows the unique adaptation of RBC in their typical slipper or bullet shape to flow within narrow capillaries. This shape change from biconcave to slipper shape is important for their unhindered passage through the narrow gaps of the microcir culation. From the fluid dynamic point of view, …