Morphometric Analysis of Preterm Fetal Pulmonary Development in the Sheep Model of Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) in humans carries high mortality/morbidity attributed to associated pulmonary hypoplasia. An understanding of the effects of CDH on fetal lung growth is important for development of successful treatments. This study aimed to quantitate structural differences between normal and CDH-affected preterm lamb lungs. We hypothesized that (a) pulmonary hypoplasia is present in preterm CDH-affected lungs; (b) the relative degree of pulmonary hypoplasia increases with gestation; and (c) the left upper lobe (LUL) is affected most.

Fetal lambs were allocated to two groups. One group underwent surgery (72–74 days gestation) inducing CDH. Both groups (n = 7, n = 7) were delivered by cesarean section at 129 days (term: 145–149). Lungs were obtained at autopsy, were inflation-fixed, processed for histology, and morphometry was performed.

Preterm lungs of CDH-affected lambs in comparison to those of normal lambs demonstrated a reduction in the following: lung weight (37.7 g vs. 116.3 g); lung weight:body weight (0.012 vs. 0.040); fixed lung volume (33.6 ml vs. 96.9 ml); gas-exchange surface area (4.56 m² vs. 13.70 m²); parenchyma:nonparenchyma (59:41 vs. 72:28); and parenchymal airspace:tissue (16:84 vs. 35: 65). Non-parenchyma connective tissue was increased (58%), airspaces were more numerous (1077/mm²) and smaller (perimeter 76.6 μm), gas-exchange surface density (2394 cm⁻¹) was greater and capillary loading (0.04 ml/m²) was reduced compared to preterm normal lung (49%; 778/mm²; 108.7μm; 2003 cm⁻¹, 0.11 ml/m², respectively). The LUL was affected most.

These data quantitate pulmonary hypoplasia in preterm CDH-affected lambs. Comparisons with published data indicate increasing relative hypoplasia as gestation proceeds. Fetal interventions will affect lung development, depending on timing, with intervention still likely to be worthwhile during late gestation.