Increased fragility of pulmonary capillaries in newborn rabbit

Abstract

The pulmonary capillaries of neonatal lungs are potentially vulnerable to stress failure because of the complex changes in the pulmonary circulation that occur at birth. We perfusion fixed the lungs from nine anesthetized newborn rabbits at capillary transmural pressures (Ptm) of 5 ± 5, 10 ± 5, and 15 ± 5 cmH2O. Normal microscopic appearances were seen at Ptm values of 5 ± 5 and 10 ± 5 cmH2O, but massive airway edema was observed in lungs perfused at a Ptm of 15 ± 5 cmH2O. Consistent with this, no disruptions of the alveolar epithelium were observed at Ptm values of 5 ± 5 cmH2O, but mean values of 0.11 and 1.22 breaks/mm epithelium were found at Ptm of 10 ± 5 and 15 ± 5 cmH2O, respectively ( P < 0.05 for 5 ± 5 vs. 15 ± 5 cmH2O). These pressures are in striking contrast to those in the adult rabbit in which, by a similar procedure, a Ptm of 52.5 cmH2O, is required before stress failure is consistently seen. We conclude that stress failure of pulmonary capillaries in newborn rabbit lungs can occur at Ptm values of less than one-third of those that are required in adult lungs.