Systemic venous collapse in man

Abstract

HE PHYSICAL conditions and the physiologic consequences of venous collapse have been the subject of various papers.1-21 This phenomenon occurs when a vein descends through a gaseous medium (veins in an elevated arm); in this case the venous cross section is reduced to a minimum, and lateral pressure is zero all along the vein, being equal to that of the surrounding medium. The same phenomenon also appears when a vein passes from a medium of higher to une of lower pressure (systemic venous trunks on entering the thorax). Then the following venous segments can be distinguished: (1) a precollapse segment having a pressure, which, whatever the flow, is practically identical to that of the extrapleural medium having higher pressure; (2) a postcollapse segment having a pressure which is normally similar to that of the pleural medium of lower pressure and (3) an intermediate segment, the cross section of which is more or less reduced according to the flow. A sharp drop of pressure takes place in this portion.