Quantitative Aspects of the Collapse Factor in Relation to Venous Return

Abstract

Fifty two dogs were used in expts. to study the effect of the collapse factor on the venous return of blood to the heart. It was found that as long as the venous pressure in the thoracic veins was greater than the intra-abdominal pressure, it was this thoracic venous pressure which was the major determinant of venous pressures in the lower part of the body, but, when the intra-abdominal pressure was greater than the thoracic venous pressure, it was the intra-abdominal pressure which was more important as a determinant of venous pressure in the lower part of the body. Quantitative data illustrate that the vena cava, except in the region of the liver, collapses immediately and essentially completely when there is slight elevation of intra-abdominal pressure above the inferior vena caval pressure. When negative pressure in the veins of the thorax, as measured in an open chest expt., reaches a critical value of approx. -5.3 mm. Hg, a still further increase in the negative pressure fails to cause additional increase in venous return.