Fetal lung growth after short-term tracheal occlusion is linearly related to intratracheal pressure

Prenatal tracheal occlusion (Tb) has been shown to accelerate fetal lung gr owth, yet the mechanism is poorly understood. The goal of this study was to determine the relationship between fetal intratracheal pressure (Pitr) and fetal lung growth after TO. Fetal lambs underwent placement of an intratra cheal catheter and a reference catheter at 115-120 days gestation (term, 14 5 days). Fetal Pitr was continuously controlled at three levels thigh, 8 mm Hg; moderate, 4 mmHg; low, 1 mmHg) by a servo-regulated pump. The animals w ere killed after 4 days, and the parameters of lung growth were compared. L ung volume (136.0 +/- 16.7, 94.9 +/- 9.7, 55.5 +/- 12.4 ml/kg), lung-to-bod y weight ratio (6.31 +/- 0.70, 4.89 +/- 0.38, 3.39 +/- 0.22%), whole right lung dry weight (3.01 +/- 0.29, 2.53 +/- 0.15, 2.07 +/- 0.24 g/kg), right l ung DNA (130.0 +/- 11.3, 116.7 +/- 8.6, 97.5 +/- 10.9 mg/kg), and protein c ontents (1,865.5 +/- 92.5, 1,657.6 +/- 106.8, 1,312.0 +/- 142.5 mg/kg) in h igh, moderate, and low groups, respectively, all increased in the moderate compared with the low group and increased further in the high compared with the moderate group. Morphometry confirmed a stepwise increase in the volum e of respiratory region and alveolar surface area. We conclude that lung gr owth in the first 4 days after TO is closely correlated with fetal Pitr, of fering additional evidence that an increase in lung expansion is one of the major factors responsible for TO-induced lung growth.