SummaryThe present study was designed to obtain quantitative data on the extent of portocaval shunting and the time course of closure of the ductus venosus in newborn lambs. Experiments were canducted on eight newborn lambs prepared with chronic portal catheters. The time course of the postnatal closure of the ductus venosus was determined by following the distribution of radiolabelled microspheres injected into the lamb's portal vein 24,48,%, and 168 hr after birth. The fraction of the portal blood flow which bypassed the liver was highly variable. In some animals, the ductus venosus was almost completely closed when the first microspheres were injected 24 hr after birth. In others, almost 40% of the portal blood flow bypassed the hepatic circulation at this time. On average, only 77% of the portal blood flow was directed to the liver in the 1-day lambs. In most cases, closure had occurred by 48 hr after birth, but some animals continued to divert a significant fraction of the portal flow away from the hepatic circulation.
SpeculationAt birth, the umbilical perfusion of the liver ceases and the hepatic circulation shifts to a much greater reliance on its portal blood flow. Patency of the ductus venosus during the 1st wk after birth may divert a sizeable fraction of the portal blood flow away from the liver and reduce the hepatic blood flow to levels which limit oxygen exchange and the development of metabolic functions in the postnatal period.The liver blood supply is greatly affected by the collapse of the placental circulation at birth. In utero, umbilical venous blood provides the liver with 80% of its blood flow (17) and almost all of its oxygen supply (5). The portal venous blood is poorly oxygenated and distributed primarily to the right side of the organ (5, 14). Because there is a negligible flow through the hepatic artery (10, 17), the loss of the hepatic umbilical flow at birth removes the main source of oxygen and begins a difficult period of transition as the liver circulation shifts to a much greater reliance on its portal inflow.Measurements of portal blood flow obtained in the immediate postnatal period indicate that it is not much greater than the equivalent flow in the fetus (2). However, it must now perfuse a mass of tissue five times greater than the prenatal distribution (17). During this time continued patency of the ductus venosus may further compromise the hepatic circulation by operating as a portocaval shunt. In human infants, as well as sheep and dogs, it is known that this vessel remains partly open after birth (1 1, 14) but the time course of its closure and the fraction of the portal flow it diverts are unknown. The present study was designed to obtain quantitative data on the extent of portocaval shunting and the time course of closure of the ductus venosus in newborn lambs.
MATERIALS AND METHODStional ages that ranged from 144-148 days and none experienced complications during labor. All lambs were healthy, energetic, and nursing freely from the ewe.The portal vein catheter was im...
The rate of ascites formation or reabsorption was recorded in anesthetized cats using the technique of intraperitoneal plethysmography. Hepatic venous pressure was increased using an extracorporeal circuit to drain effluent blood from the liver. When the intraperitoneal pressure was set to zero, elevation of hepatic venous pressure increased portal pressure and produced a constant rate of ascites formation. However, equivalent increments of portal pressure without elevation of hepatic venous pressure did not cause ascites formation, indicating that the liver was the source of ascites when hepatic venous pressure was increased. The rate of ascites formation was proportional to hepatic venous pressure, but elevation of the intraperitoneal pressure reduced the transsinusoidal pressure gradient responsible for fluid filtration from the liver. Although this reduced the rate of ascites formation, a secondary effect partly opposed this reduction in filtration rate. From this study and from previous work, there are now quantitative data showing that the intraperitoneal pressure is an important factor which accelerates the rate of reabsorption and decreases the rate of formation of ascites to bring these processes into equilibrium.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.