Respiratory function in lambs after in utero treatment of lung hypoplasia by tracheal obstruction.

Tracheal obstruction (TO) stimulates growth of hypoplastic lungs in the fetus, but there is little knowledge of subsequent postnatal respiratory function. We have determined the effectiveness of TO in fetal sheep with existing lung hypoplasia in restoring postnatal respiratory function. Lung hypoplasia was induced by lung liquid drainage from 112 days of gestation to term ( approximately 148 days). We used an untreated group (ULH), a treated group (TLH) in which the trachea was obstructed for 10 days, and a control group. ULH lambs died within 4 h of birth. TLH lambs were hypoxic for the first week and were hypercapic at 2 days. Pulmonary diffusing capacity, gas volumes, and respiratory compliances were not different between control and TLH lambs. Minute ventilation was not different between the two groups; however, tidal volumes were lower and respiratory frequencies were higher in TLH lambs than in controls for 2 wk after birth. We conclude that 10 days of TO in the presence of initial lung hypoplasia prevents death at birth and returns most aspects of pulmonary function to normal by 1-2 wk after birth.