Pulmonary Vascular Changes with Chronic Unilateral Pulmonary Hypoxia

One main bronchus was ligated in each of twelve dogs and three calves. In eight of the animals, the bronchus reopened spontaneously with a 2 to 4 mm aperture permitting re-expansion of the associated lung. Both smooth muscle hyperplasia and hypertrophy developed in small arteries of the poorly ventilated dog lungs. In the calves, muscular hyperplasia and hypertrophy developed in small pulmonary veins of the hypoxic lungs. Since arterial pressures and pulmonary arterial oxygen saturation were presumably identical in hypoxic and control lungs, changes in vascular muscle are postulated to be the result of altered oxygen tension of the surrounding alveolar gas.