Pulmonary arterial hypertension induced by distention of the main pulmonary artery in conscious newborn, young, and adult sheep

Abstract

Distention of the main pulmonary artery by balloon inflation in sheep results in presumably reflex elevation of pulmonary arterial pressure and resistance distal to the balloon. This response to main pulmonary artery distention is significantly greater in newborn lambs than in older lambs or adult sheep. In several of the newborn lambs, pulmonary artery pressure was raised to supra- systemic levels. Further, in some of the newborn animals, these increases in pulmonary artery pressure and resistance were sustained after deflation of the balloon for periods up to 2 hr. The functional significance of this pulmonary hypertension reflex was not elucidated. However, the data strongly suggest that this reflex may contribute to the maintenance of high pulmonary vascular resistance during fetal and early neonatal life. Speculation: Proximal distention of the main pulmonary artery induces a positive feedback reflex which significantly elevates pulmonary artery pressure and resistance. We postulate that this reflex operates in conjunction with hypoxia to maintain high pulmonary vascular resistance in the fetus. It is possible that at birth this reflex mechanism operates in reverse to help lower the pulmonary vascular resistance smoothly, thus avoiding volume overload of the neonatal lungs and left ventricle. Finally, we postulate that this reflex may play a role in the pathogenesis of the persistant fetal circulation syndrome (7). © 1980 International Pediatric Research Foundation, Inc.