Reversal of Pulmonary Hypertension by Prolonged Oxygen Administration to Patients with Chronic Bronchitis

Established pulmonary hypertension associated with hypoxemia in patients with chronic bronchitis is probably secondary to hyperplasia of the smooth muscle of pulmonary arterioles. To investigate the possibility that this increase in pulmonary arterial pressure was reversible, the floating catheter technique was used to study the effects of continuous administration of oxygen for 4 to 8 weeks on the pulmonary circulation. In six patients, there was a gradual fall in pulmonary arterial pressure, the mean pressure for the group being 42.5 mm Hg before, and 32.3 mm Hg after, the period of oxygen administration. All measurements were made when the patients breathed air. There was no change in cardiac output. Hematocrit decreased from 51.4% to 42.5%, but total blood volume remained unchanged. It has been shown previously that brief inhalation of oxygen can cause a slight temporary reduction in the pulmonary hypertension associated with chronic bronchitis and anoxemia. The present findings show that the residual, established hypertension is also reversible if oxygen therapy is continued for weeks. It is suggested that this reversal may be brought about by regression of the muscular hyperplasia of the small pulmonary vessels consequent to longterm relief of hypoxia.