Hypoperfusion and hyperperfusion in the immature lung: Pulmonary arterial development following ligation of the left pulmonary artery in the newborn pig

Abstract

The left pulmonary artery and ductus arteriosus were ligated in 14 newborn pigs. Animals were put to death at intervals between 2 and 24 weeks of age. In each animal a cardiac catheterization was performed before sacrifice. Pulmonary arterial development in both lungs was studied by applying quantitative morphometric techniques to the infected and inflated specimens. In the right lung, pulmonary arterial pressure and resistance fell to normal after birth; however, structurally, muscularity remained high in arteries less than 75 mu in diameter. Size and number of intra-acinar arteries increased normally, not excessively, with age despite the abnormally high flow. After 16 weeks in all animals, muscularity increased significantly in arteries of all sizes; mean pulmonary arterial pressure was 20 to 35 mm Hg, the pulmonary--systemic pressure ratio was 0.21 or more, and total pulmonary vascular resistance was 0.16 to 0.4 torr (ml/min/kg) (normal, 0.08). In the left lung, the axial pulmonary artery and its branches were small, decreasing in size with age, and its elastic wall structure was disorganized. Small preacinar arteries showed obliterative change in the majority of animals put to death at 16 weeks or more. Within the acinus, however, the bronchial arterial blood supply ensured almost normal postnatal pulmonary arterial development, the vessels increasing in size and number although muscularity was reduced. Thus failure to perfuse one pulmonary artery in the immature animal changes growth and development of both lungs, and the findings are discussed in relation to the hyperperfused and hypoperfused lung in childhood.