[Flow characteristics of blood and its therapeutic modification].

Blood viscosity is a major determinant of blood flow. Whole blood is a non-Newtonian fluid, i.e. its viscosity increases with decreasing shear rate (flow rate). Blood viscosity is determined by hematocrit, plasma viscosity, red cell aggregation and red cell deformability. The rheological therapy for high hematocrit is phlebotomy, and for high plasma viscosity and red cell aggregation it is plasmapheresis or hemodilution. Much effort has recently been devoted to influencing red cell deformability, the major determinant for flow in the microcirculation, by pharmacological means. No improvement in red cell deformability, however, has been unequivocally demonstrated for any drug available today.