[Venous hemodynamics of the lower limbs].

Low pressure venous return results from several different pump systems. Blood flow and velocity depend on sympathetic tone and contraction of the veins modulating distensibility. In patients with chronic venous insufficiency, different components including hyperdistensibility, hyperpressure, valve failure, back-flow and stasis, lead to a vicious circle. These elements modify the venous wall and lead to hyperdistension producing modified distensibility and/or formation of varicose veins. Endothelial and smooth muscle cells participate in these changes. Smooth muscle cells play a major role: some hypertrophy and/or lose their contractility, synthesizing and sometimes rapidly destroying tissue. These changes in the circulation, sometimes increased by inflammation and thrombosis, affect microcirculatory haemodynamics with a variable delay. The venous system, even when pathological (as long as it is not totally invaded by fibrosis) responds to a large number of relaxing or constricting pharmacological agents, justifying their therapeutic value.