Angiocardiographic and Metabolic Studies in Immersed Lamb Fetuses Perfused Through an Artificial Placenta

Abstract

Using angiocardiography we studied twelve premature lambs of 130–145 days gestation (2.3–4.0 kg) obtained at caesarian section and maintained in a filtered and thermoregulated bath of synthetic amniotic fluid. By selectively varying the oxygen concentration in the gas compartment of the membrane lung we were able to control the level of blood oxygen tension independent of pH, PCO2, and placental flow. Within 20 min after raising fetal umbilical pO2 from 13–20 to 40–60 mm Hg there was almost total conversion of the fetal circulatory pattern to that of the newborn. The I.D. of the ductus arteriosus constricted from 4.1 mm to less than 1.0 mm; pulmonary circulation time decreased from more than 18.4 to 2.4 sec. These findings were not affected by metabolic or respiratory acidosis. Inferior vena cava injections illustrated complete closure of the foramen ovale; no opacification of the left atrium occurring at pO2 from 40–60 mm Hg with a constricted ductus arteriosus. Oxygen consumption of fetuses paralyzed with succinylcholine measured continuously by spirometry averaged 6–7 ½ cm3/kg/min while carbon dioxide production was measured continuously by infrared analysis of effluent gas at 7–8.5 cm3/kg/min. Respiratory quotients consistently greater than one were observed with blood glucose levels above 100 mg%. Four fetuses were delivered following angiocordiographic study; two are long-term survivors.