Lung parenchyma at maturity is influenced by postnatal growth but not by moderate preterm birth in sheep

Background: We have recently shown that moderate preterm birth, in the absence of respiratory support, altered the structure of lung parenchyma in young lambs, but the long-term effects are unknown. Objectives: To determine whether structural changes persist to maturity, and whether postnatal growth affects lung structure at maturity in sheep. Methods: At approximately 1.2 years after birth, lung parenchyma of sheep born 14 days before term (n = 7) was stereologically compared with that of controls born at term (n = 8, term approx. 146 days). Results: Preterm birth per se had no significant effect on lung volume, alveolar number and size, and thicknesses of the alveolar walls and blood-gas barrier. After combining the preterm and term groups, we examined the effects of postnatal growth rates on lung parenchyma. Slower-growing sheep (SG; n = 7: 4 preterm, 3 term) were compared with faster-growing sheep (FG; n = 8: 3 preterm, 5 term). At approximately 1.2 years, the right lung volume, relative to body weight, was significantly lower in SG than FG sheep (p <0.05) and alveolar number was significantly lower by approximately 44 . The total alveolar internal surface area of the right lung of SG sheep was 38 smaller than in FG sheep; it was also significantly lower when related to both lung and body weight. Conclusions: Our data suggest that moderate preterm birth does not cause persistent alterations in lung parenchyma. However, slow postnatal growth in low-birth-weight sheep results in smaller lungs with fewer alveoli and a lower alveolar surface area relative to body weight.