Fluid dynamics in the hepatoperitoneal system

Abstract

A study was made of arterial pressure, portal pressure, inferior vena caval pressure, hepatic interstitial pressure (implanted capsule technique), prenodal lymph flow, and the protein concentration in plasma and lymph in the anesthetized dog under normal conditions and during graded venous hypertension resulting from inferior vena caval occlusion. Under control conditions, portal, interstitial, and inferior vena caval pressures were 7.0, 5.8, and 2.0 mm Hg, respectively, and the lymph/plasma protein concentration ratio was 0.95. During acute venous hypertension, 64% of the inferior vena caval pressure increase was transmitted to the hepatic interstitium, and lymph flow increased by 63% of control for every 1 mm Hg increment in interstitial pressure. The lymph/plasma protein concentration ratio did not change significantly during venous hypertension, indicating that: (1) the reflection coefficient of the sinusoidal wall for the major plasma proteins is close to zero, and (2) protein transport across the microvascular wall is due mainly to bulk flow. Using portal, interstitial and inferior vena caval pressures as limits for possible values of sinusoidal pressure, our data suggest that (1) control sinusoidal pressure was between 5.8 and 7.0 mm Hg, and (2) approximately 90% of the increase in inferior vena caval pressure was transmitted to the sinusoids. In a second group of dogs, changes in pressure within the peritoneal cavity were monitored as the volume of fluid within the peritoneum was increased in order to simulate ascites. When the fluid volume in the peritoneal cavity was very low the compliance of the cavity was found to be 10.8 ml per mm Hg per kg of body weight. Compliance of the peritoneal cavity was found to decrease as intra-abdominal pressure increased. In one animal with a chronically distended abdomen and confirmed ascites, the hepatic interstitial pressure was 18 mm Hg. The high compliance of the peritoneal cavity at low volumes provides an excellent site for the accumulation of fluid which would otherwise engorge the liver during venous hypertension...