Cardiac Output and Organ Blood Flows in the Baboon Fetus

The regional distribution of the cardiac output was measured for the first time in six normal baboon fetuses of 150–160 days’ gestation by the injection of radiolabelled microspheres into the superior and inferior vena cavas and the umbilical vein. Umbilical blood flow as estimated by the antipyrine equilibration technique was 104 ± 32 ml/min/kg and together with the distribution of radioactivity provided the basis for calculating organ blood flows. Cardiac output was 287 ± 97 ml/min/kg. 55.4 ± 16.4% of umbilical blood flow passed through the ductus venosus and there was no evidence of preferential streaming of ductus venosus blood as described in the rhesus fetus. Brain blood flow was 13.6 ± 1.2% of cardiac output while 38.7 ± 8.5% was distributed to the placenta and 8.8 ± 5.4% to the lungs. Comparisons were made between these six baboon fetuses and rhesus and sheep fetuses studied near term in acute experiments.