Main pulmonary artery distention: a potential mechanism for acute pulmonary hypertension in the human newborn infant.

Balloon-induced distention of the main pulmonary artery causes acute pulmonary hypertension and reflex pulmonary vasoconstriction in animals. Pulmonary artery pressure responses caused by MPA balloon inflation were measured in ten human newborn infants with cardiac failure (n = 5) or persistent fetal circulation (n = 5). During balloon inflation distal mean PAP increased significantly while cardiac rate remained unchanged. MPA distention caused greater increases of PAP in those infants with lower resting PAP. The greatest balloon-induced increases of PAP were observed in infants recovering from PFC. The existence of a pulmonary artery reflex and its possible role in the regulation of the human fetal and neonatal pulmonary circulation is discussed.