Influence of body position and pneumoperitoneum on respiratory variation of venous return in anesthetized dogs.

Abstract

Blood flow in the vena cava was measured in anesthetized dogs in supine, lateral, or prone position by a catheter velocity probe at four levels, i. e., above and below the veno-atrial junction and above and below the confluence of the renal veins, with the diameter of the vena cava fixed Teflon rings placed around it. Also the influence of pneumoperitoneum at atmospheric pressure on venous return was examined in supine position. In supine position there was an increase of venous return in the thoracic venae cavae and of calculated hepatic outflow during inspiration, whereas flow in the abdominal vena cava showed less and reversed variations as compared with the thoracic inferior caval venous pattern, i.e., a trough during inspiration and a peak during early expiration. Pneumoperitoneum reduced the inspiratory increase of thoracic inferior vena cava flow and of hepatic outflow. Lateral and prone positions induced a decrease or early leveling off of the inspiratory increase of flow in the thoracic inferior vena cava and of hepatic outflow. Superior caval venous flow remained almost unchanged with postural change. In all positions renal outflow did not show any clear-cut relationship with respiration. These variations of pattern of vena cava flow and hepatic outflow were attributed to an increase in the resistance of the vena cava in the infradiaphragmatic part, induced by the change of body position, as shown by an increase of the preinspiratory caval venous pressure difference between thorax and abdomen to 5.3±0.92 cm H2O (mean±S.D.,n=14) in lateral position, and to 6.5±0.81 cm H2O (n=4) in prone position from 2.0±0.85 cm H2O (n=18) in supine position (p<0.001 for the increase from supine position).