Viles, Peter H.

Isolated cat lungs perfused at constant flow (75 ml/min per kg total body weight) were ventilated with gases of varying CO 2 content (0 to 10%), 20% O 2 , and the balance N 2 . Tidal volume was constant, and airway pressure did not change. Left atrial pressure was held constant, and changes in pulmonary artery pressure (PPA) were taken to reflect changes in pulmonary vascular resistance. Progressive hypercapnia (Pco 2 = 0 to 60 mm Hg) resulted in an increase in PPA as pH decreased. Equivalent degrees of acidosis, produced by the infusion of 0.3 N lactic acid, resulted in a higher PPA. Changes in PPA produced by lactic acid were reversible with 0.89 M sodium bicarbonate. With Pco 2 constant, and pH changed by lactic acid or sodium bicarbonate infusion, PPA was higher in lungs ventilated with room air (Pco 2 = 0) than in those ventilated with 5 or 10% CO 2 (Pco 2 = 30 or 60 mm Hg) at the same hydrogen ion concentration of the perfusate. These findings can be explained by two opposing actions of CO 2 on pulmonary vessels: a dilator action due to the direct effect of CO 2 and a constrictor action caused by the increase in hydrogen ion concentration.

Obstructive pulmonary vascular disease (PVD) was evaluated in lung sections taken at autopsy in 53 patients with complete transposition of the great arteries. Twentythree had intact ventricular septa and 30 had ventricular septal defects. Children of similar age and associated defects had widely differing degrees of PVD and presented a spectrum of disease. In a small number of patients, the presence of pulmonic stenosis (congenital or acquired by pulmonary artery banding in infancy), a small ventricular septal defect, or a large atrial septal defect was not protective against the development of severe PVD. The findings of this study demonstrate the need for thorough hemodynamic evaluation of patients with complete transposition of the great arteries prior to repair by present technics. In addition, operation should probably be performed as soon as technically feasible.