Morphometric analysis of pulmonary development in the sheep following creation of fetal diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) in humans is relatively common and associated with high mortality attributed mainly to pulmonary hypoplasia. Previous animal models have induced CDH late in gestation, in contrast to the human situation, and only limited morphometric analyses have been reported. We undertook early surgical creation of CDH in fetal lambs, days 72-74 of gestation (n = 8), with unoperated lambs (n = 8) as controls. At 143 days (term = 145-149) a cesarean section was performed and the lungs were obtained, inflation fixed, divided into lobes, and processed for morphometry. In the CDH group the total lung volumes (51.3 mL compared to 223.8 mL) and gas exchange surface areas (5.85 m2 versus 26.43 m2) were less than one quarter of control values. Capillary loading was reduced from 0.3 mL/m2 in controls to 0.12 mL/m2 in CDH and parenchymal volume reduced from 77% in controls to 57% in CDH. Within parenchyma, gas exchange tissue volume was increased in CDH (66%) compared with controls (50%). CDH lungs had primitive air sacs/alveoli that were smaller (perimeter 83 microns) and more numerous (1321 per mm2) than in controls (perimeter 132 microns, 504 per mm2). The left lung and left upper lobe were affected most. Induction of CDH in the lamb at this early age results in quantifiable, reproducible pulmonary hypoplasia from which comparisons can be made with the human condition.