[Blood viscosity. Measurement and applications (hyper--and hypoviscosity syndromes) (author's transl)]

Blood has particular rheological properties which partly condition its flow, especially in capillary vessels, and its ability to deliver oxygen. It is not subject to gravitation, pseudoplastic, thixotropic and visco-elastic. Blood viscosity depends upon macroscopic factors, such as erythrocyte aggregation and deformability. Hyperviscosity is observed in cases of increased haematocrit (polycythaemia and relative polycythaemia), increased serum proteins and changes in protein balance (e.g. rise in fibrinogen and immunoglobulins, fall in albumin) as seen in inflammation and dysglobulinaemia, drop in temperature (hypothermia), increased erythrocyte aggregation (shock, fat embolism) or imparied deformability due to various acquired or inherited disorders of red cell membrane or cytoplasma (e.g. sickle cell anaemia, renal failure, hyperlipoproteinaemias, thrombosis, diabetes). The various factors may be combined, as in diabetes. Conversely, hypoviscosity may result from decreased haematocrite, fall in blood proteins and fibrinogen, or hyperthermia. Hyperviscosity can be corrected by acting on its various constituents. Treatments include haemodilution, plasmapheresis, anti-aggregants and drugs improving red cell deformability.