[Rheologic particulars of venous flow. Physiopathologic consequences]

Abstract

Hemorheological parameters must be taken into account for a better knowledge of venous flow properties. The postcapillary venules are the region of lowest shear rates and therefore the region of highest whole blood viscosity. Red cell aggregation plays a major role in blood viscosity, especially at low shear rate. This microrheological parameter can be increased in pathological circumstances, including a low capillary flow, venular insufficiency, elevated hematocrit, high levels of acute phase proteins. At the level of the capillaries, microcirculatory stasis leads to a low oxygen supply and consequently to poor metabolic state lowering local ATP levels. As a result, both platelet and white blood cell functions are compromised. Hemorheological studies have shown that both deep venous thrombosis and chronic venous insufficiency are associated with high blood viscosity mainly due to an increased red cell aggregation. This hemorheological vicious circle--stasis promoting hyperviscosity leading to further stasis--could be broken up by therapeutic intervention including hemodilution, fibrinolytic drugs or other specific agents.