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 o f the veins modulating distensibility. In patients with chronic venous insufficiency, different components including hyperdistensibility, hy perpressure, valve failure, back-flow and stasis, lead to a vicious ci rcle. These elements modify the venous wall and lead to hyperdistensio n producing modified distensibility and/or formation of varicose veins . Endothelial and smooth muscle cells participate in these changes. Sm ooth muscle cells play a major role: some hypertrophy and/or lose thei r contractility, synthesizing and some times rapidly destroying tissue . These changes in the circulation, sometimes increased by inflammatio n and thrombosis, affect microcirculatory haemodynamics with a variabl e delay. The venous system, even when pathological (as long as it is n ot totally invaded by fibrosis) responds to a large number of relaxing or constricting pharmacological agents, justifying their therapeutic value.