THE EFFECTS OF THE PATENT DUCTUS ARTERIOSUS ON THE CIRCULATION.

The operation for ligation of the patent ductus arteriosus, as described by Gross and Hubbard (1), presented an opportunity to study the circulatory dynamics of this congenital anomaly. A patent ductus arteriosus is a vascular communication between the aorta and the pulmonary artery. Because the blood pressure is normally higher in the aorta than in the pulmonary artery, and because the arterial blood of patients with patent ductus arteriosus has been found to be saturated with oxygen to a normal degree, it has been assumed that in uncomplicated cases the flow of blood through the ductus is in the main from aorta to pulmonary artery. The amount of blood passing through the ductus per unit of time was calculated by Plesch in 1909 (2); however, he used a method which in the light of present knowledge is not valid. The purpose of this paper is to report the results of quantitative studies of the circulation in patients with patent ductus arteriosus. The problem is further elucidated by measurements in animals in which a situation similar to a patent ductus arteriosus has been brought about by operation. In normal individuals and in those with certain types of cardiac abnormalities the output of the heart may be determined by the foreign gas method of Marshall and Grollman (3), provided that samples of the foreign gas from the lung-bag mixture are obtained after equilibrium has been reached and before recirculation to the lungs has occurred. This method is not applicable to patients with patent ductus arteriosus because, when such patency is present, a portion of the foreign gas absorbed by the blood during its passage through the capillaries of the lung is almost immediately returned to the lungs through the ab-