Inflow to a segment of deep vein is through intake valves from perforating veins as well as from the deep vein segment below. Outflow is through an outflow valve to the deep vein segment above. Squeezing of the vein segment occurs when muscle contraction increases the pressure within a fascial muscle compartment. Just like a sphygmomanometer, the calf muscle pump can achieve pumping pressures of several hundred mm Hg before valve failure occurs. Venous Pathology Venous pathology develops when venous return is impaired for any reason.
Venous pathology can be deep, superficial, or mixed.
Immediately after ambulation, the normal pressure within the veins of the lower extremity is extremely low because both the superficial and deep venous systems have been emptied by a normally functioning muscle pump. Normal inflow to the lower extremity veins is purely via arterial inflow, thus the normal venous system will be more or less refilled after 3 to 5 minutes of standing. When the entire venous system is filled, the valves float open and venous pressure rises to a maximum exactly equal to the height of the standing column of venous blood from head to foot. This condition triggers an urge to move the legs, activating the muscle pumps and re-emptying the legs. The immediate postambulatory venous pressure will be nearly as high as the pressure after prolonged standing.