THE RELATIONSHIP BETWEEN RESPIRATION, PRESSURE AND FLOW DISTRIBUTION IN THE VENA-CAVA AND PORTAL AND HEPATIC VEINS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 151  (6) , 753-763
Abstract
Factors affecting blood movement in the main vessels of the venous system and the changes in pressure and flow values in the vena cava and portal and hepatic veins were simultaneously recorded and related to the phases of the respiratory cycle. The experiments were done in rabbits subjected to nembutal anesthesia with open abdomen, closed chest and spontaneous respiration. An asymmetric pressure gradient in the vena cava centered around the diaphragm with larger pressure differences in the thoracic segment are indicated; no pressure gradient in the portal vein and a sharp gradient of possible functional significance at the caval end of the hepatic veins was shown. Portal, hepatic and abdominal caval pressures were positive, but above the diaphragm, vena cava pressure values were predominantly negative. Flow was continuous, unequally distributed throughout the components and fluctuating alternatively during 1 respiratory cycle. Maximal pressure and flow values in the portal and hepatic veins were concomitant with the lowest values in the vena cava and closely related to respiration. The distribution of opposite pressure and flow values within the components and their integration during 1 respiratory cycle suggest that, in the process of venous return, each component and each segment fulfills simultaneously different functions co-ordinated by respiration and cardiac activity.

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