Cardiovascular hemodynamics in the fetal lamb before and after lung expansion

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Abstract
Cardiovascular hemodynamic studies were carried out on fetal lambs before and after lung ventilation as well as before and after cord clamping. The findings are as follows:1) Before lung expansion, pressures, output, and work in the right side of the heart are greater than those in the left side. This relation is reversed promptly after lung expansion. 2) When compared to adults, effective fetal cardiac output is high before lung expansion and falls significantly after lung expansion. 3) In the fetus, total pulmonary vascular resistance is considerably higher than systemic resistance. This relation is reversed immediately after lung expansion. 4) In the fetus, the flow of blood in the aorta and pulmonary artery is largely governed by inertial factors. 5) Cord clamping increases systemic resistance through elimination of low vascular resistance of the placental bed.