The Role of the Umbilical Sinus in the Regulation of Placental Vascular Resistance

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Abstract
The role of the umbilical sinus – ductus venosus complex in the regulation of umbilical venous and placental vascular resistance was investigated in 12 near term exteriorized fetal lambs before and after the induction of mild and severe hypoxia. Mild maternal hypoxia caused increases in the umbilical vein and inferior vena cava pressures and a decrease in the umbilical blood flow rate. Severe maternal hypoxia caused an increase in the inferior vena cava pressure and a decrease in the umbilical blood flow, both of which were statistically significant. During mild maternal hypoxia the placental vascular resistance increased 11 % and the umbilical sinus vascular resistance increased 24%, while during severe hypoxia the increases were 17 and 66% respectively, thus demonstrating a greater sensitivity of the umbilical sinus vasculature to the stress of hypoxia and emphasizing its role in placental vascular resistance.

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