Studies on Ductus Arteriosus Circulation

Abstract

Summary of Part I Isolated ductus arteriosus vessels obtained from fetal lambs prior to lung expansion were perfused with blood of varying pO₂ at a constant temperature and pressure. Flow decreased progressively as the pO₂ of the perfusing blood increased. The changes were more striking at oxygen pressures greater than 50 mm Hg. Summary of Part II The effects of ventilating the lungs with oxygen and nitrogen on the pulmonary artery and ductus arteriosus circulation were investigated in near term fetal lambs with and without intact umbilical circulation. Oxygen ventilation increased transitorily the ductus flow through widening of the pressure difference between the pulmonary artery and aorta. Ductus flow was strikingly reduced as oxygen ventilation progressed. Pulmonary artery pressure fell while aortic pressure rose. These changes could be reversed with nitrogen. Nitrogen ventilation also produced an initial increase in ductus flow through an increase in the differential pressure between the pulmonary artery and aorta. Prolonged administration of nitrogen depressed ductus flow together with pulmonary flow and systemic arterial pressure. These changes were probably related to the direct effects of nitrogen and hypoxia on the heart and pulmonary circulation. Interruption of the umbilical circulation reduced temporarily ductus and pulmonary artery flows. This fall was related to circulatory readjustments caused by abrupt elimination of the placental circulation. From the in vivo and in vitro studies, it appears that at least three factors contribute to the control of blood flow in the ductus the pO₂ of the blood; the pulmonary artery flow; and the differential pressure between the pulmonary artery and aorta.