Effect of breathing oxygen on pulmonary artery pressure and pulmonary vascular resistance in patients with ventricular septal defect.

IN 1946 von Euler and Liljestranld' demonstrated that the pulmonary artery pressure in the eat was increased when the animal breathed a gas mixture of low oxygen content. Comparable results have been demonstrated in other species, including man.2 4 In spite of a degree of variability in the results of experiments designed to elucidate the mechanism of this response, most studies suggest that hypoxia can cause the pulmonary vessels to constrict. Further studies>5 6 on the comparative effects of breathing a gas mixture of low oxygen tension in one lung, while breathing a gas mixture of normal oxygen tension in the other suggest that constriction takes place in the vessels of the hypoxic lung. Relatively little attention has been paid to the effect exercised on the pulmonary vascular bed by high oxygen tension in the inspired air, although a fall in pulmonary artery pressure has been demonstrated in man, both with normal pulmonary circulation and with pulinonary hypertension.7-10 Further, the timing and sequence of events in relation to the change in the oxygen concentration in the inspired gas mixture have not been clearly described. The present study concerns the effect of breathing gas mixtures of high oxygen tension on the pulmonary and systemic arterial pressures and vascular resistances in 31 patients with ventricular septal defect and varying degrees of elevation of pulmonary artery pressure. Particular attention has been given to