Demonstration of Differential Effects on Pulmonary and Systemic Arterial Pressure by Variation in Oxygen Content of Inspired Air in Patients with Patent Ductus Arteriosus and Pulmonary Hypertension

Seven cases of patent ductus arteriosus with pulmonary hypertension and reversal of the usual direction of flow are described. Breathing of a low oxygen mixture either initiated or increased the reversed shunt, and breathing 100 per cent oxygen produced the reverse effect. Differences in oxygen saturation and dye-dilution curves recorded simultaneously from the radial and femoral arteries have allowed calculation of differences in the proportion of shunted blood flowing in these arteries and demonstrate that retrograde movement of blood in the aortic arch may occur.