Effects of hypoxemia and decreasing umbilical flow liver and ductus venosus blood flows in fetal lambs

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Abstract
Radioactive microsphere technique was used to determine the effects of hypoxemia and decreasing umbilical blood flow on liver and ductus venosus blood flows in 31 chronically catheterized fetal lambs. Fetal hypoxemia, produced by administering a hypoxia-inducing gas mixture to the mother, had no effect on hepatic arterial, umbilical venous, or portal venous blood flows to liver or ductus venosus. Hypoxemia also did not change resistance to blood flow through the ductus venosus. Reductions in umbilical blood flow of 25-50%, produced by partial occlusion of the fetal descending aorta, did not alter hepatic arterial or portal venous blood flows to liver or ductus venosus. Umbilical blood flow reductions of 25, 50 and 75% resulted in decreases in umbilical venous blood flow to the whole liver, although with 50% and 75% reductions the decreases were greater in the right lobe than in the left lobe of the liver. Blood flow and the pressure difference across the ductus venosus decreased with 50% and 75% reductions, so that the estimated resistance to blood flow through the ductus venosus did not change. Hypoxemia has little, if any, role in influencing liver and ductus venosus blood flows in the fetal lamb. Apparently resistance and pressure differences are important determinants of the distribution of blood flows to liver and ductus venosus in the fetus.