The Venous Pump in the Legs as a Determinant of Pulmonary Capillary Filling*

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Abstract
Passive motion of the lower extremities in upright normal men decreases the pressure in the saphenous vein at the ankle and increase breathholding diffusing capacity (DLCO). This effect is present in the first 10 seconds of passive leg motion. DLCO does not increase during passive motion of the legs in sitting subjects if the egress of blood from the legs is prevented by the inflation of thigh tourniquets to 250 mm Hg or in supine subjects. This study suggests that a portion of the increase in DLCO that occurs with exercise in an upright position is dependent upon pumping of blood from the exercising part to the lung and is independent of any generalized reflex action. It suggests further that the venous pumping mechanism is one of the determinants of pulmonary capillary filling in upright postures.