Dynamics of blood flow in the ductus arteriosus

¹ Departments of Obstetrics and Gynecology, and Physiology, University of California School of Medicine, and Department of Electrical Engineering, University of Southern California School of Engineering, Los Angeles, California

The instantaneous pulsatile flow-pressure relationships across the ductus arteriosus were studied in fetal lambs before and after progressive lung expansion. Analysis of the same flow-pressure relationship was simulated on an analog computer using a mathematical model of the fetal circulation. The results demonstrate that 1) the blood flow through the ductus has a distinctive inertial characteristic and 2) there exists an asynchrony between the ejection of the two ventricles; the ejection of the right ventricle precedes that of the left. Both these factors explain the paradox of flow across the ductus from pulmonary artery to aorta (right-to-left shunt) which is seen when the lungs are incompletely expanded and the aortic pressure is higher than the pulmonary artery pressure.

Key Words: fetal vascular dynamics • "inertiance" • ventricular • asynchrony • ductus circulation • fetal analog computer simulations

Submitted on July 15, 1964