The “After-Drop” in Venous Occlusion Plethysmograms

Venous occlusion plethysmograms from the dependent foot showed an “after-drop” in volume not seen with the foot at heart level. Factors affecting the development of this after-drop were studied. Blood flow was measured during the after-drop and corresponding changes in venous pressure recorded. The evidence obtained does not support the existing explanation that the after-drop is due to a reflex vasoconstriction. It is suggested that this phenomenon is due to a shifting of blood in the underlying vessels by the venous occlusion cuff.