Regional myocardial blood flow and oxygen delivery in fetal, newborn, and adult sheep

We measured and calculated their product, regional myocardial oxygen delivery, in unanesthetized, previously instrumented fetal, newborn, and adult sheep. In the fetus, blood flow and oxygen delivery were greater to the right ventricular free wall than to the left ventricular free wall. In the left ventricular free wall oxygen delivery increased significantly after birth and later decreased to a level in the adult that was similar to that of the fetus. There was a progressive decrease in oxygen delivery to the right ventricular free wall during the developmental period that we studied. Although the inner-to-outer blood flow ratio was significantly lower for the left and right ventricular free walls of the fetuses as compared with the newborns and adults, the ratio was greater than one in all three groups for both of the ventricular free walls. These data demonstrate that the changes that occur in the circulation after birth are associated with significant alterations in right and left ventricular myocardial blood flow and oxygen delivery, which most likely reflect changes in regional myocardial metabolic demands. In addition, there are further significant changes in regional myocardial blood flow during the transition from the newborn to adult hemodynamics.