The venous footpump: influence on tissue perfusion and prevention of venous thrombosis.

Development of the technique of video phlebo-graphy has enabled the anatomy and physiology of the venous pump in the human foot to be demonstrated.' This hitherto largely unrecog-nised organ consists of the abnormally large venae comites of the lateral plantar artery (fig 1). The plantar venous pump has a stroke volume of between 20 and 30 ml and is activated simply by weight bearing. There are three misconceptions relating to the venous return from the foot which have been disproved by video phlebography. (a) The concept of a peripheral venous pump has always embraced the idea of active muscular contraction ; however, video phlebography shows that this is not true in the foot. Passive weight bearing flattens the plantar arch, stretching the veins longitudinally, causing them to constrict 'neck down' and dislocate the blood with sufficient force to overcome the resistance of a sphygmomanometer cuff inflated to over 100 mm around the calf. This alone is adequate to return blood from the foot to the right atrium in the upright position. The foot pump has been shown to be functional in paraplegic legs.2 The blood returns in a jerky fashion with the venous valves acting as haemodynamic ratchets.2 3 (b) The belief that the plantar veins drain onto the dorsum of the foot is a second fallacy; video phlebography shows that the blood is pumped 5