Central shunt flows and pressures in the mature fetal lamb.

Two to eight days after surgery, we determined biventricular cardiac output with the microsphere-dilution method and individual ventricular output with an electromagnetic flow sensor in 12 fetal lambs. Mean biventricular output was 462 ml.min-1.kg-1. Right ventricular output was 60%, pulmonary blood flow was 6%, blood flow in the ductus arteriosus was 54%, flow through the foramen ovale was 34%, and flow in the descending thoracic aorta above the ductus arteriosus was 12% of the biventricular cardiac output. Foramen ovale flow did not correlate with the pressure difference between the atria. The flow though the foramen ovale correlated positively with the flow in the inferior caval vein. It was concluded the shunt flow through the foramen ovale is mainly determined by the kinetic energy of the blood in the "lower atrial inflow tract." Fetal systemic somatic blood flow showed a reliable negative correlation with the oxygen tension in the fetal arterial blood. This was taken as presumptive evidence for long-term autoregulation of flow in the peripheral tissues.