The Influence of Rate of Filling on Apparent Venous Distensibility in Man

Abstract

The influence of the rate of filling on the relation between venous volume and transmural pressure in the human extremity was investigated with two techniques, venous occlusion plethysmography (leg) and infusion into an isolated venous segment (forearm). Both methods revealed a quantitatively important rate-related component in the response of veins to distension; the venous volume was lower at a given transmural pressure when filling was rapid. This component can serve as a local buffering mechanism, minimizing volume changes after sudden changes in postcapillary pressure such as occur with changes of posture or blood flow. Since blood flow and apparent venous distensibility are interrelated, flow changes must be taken into account in the interpretation of studies in which venous distensibility curves determined by plethysmography are used as an index of venous tone.It has also been demonstrated that the limb supported above heart level contains a minimal volume of blood which is not altered by external pressures up to 40 mm Hg.