RESPIRATORY-FUNCTION IN LAMBS AFTER PROLONGED OLIGOHYDRAMNIOS DURING LATE-GESTATION

Our aim was to determine the effects of oligohydramnios during the las t third of ovine gestation on respiratory function in lambs during the ir first postnatal month. To induce oligohydramnios, amniotic and alla ntoic fluids were drained from pregnant ewes, starting at 109.0 +/- 2. 3 d of pregnancy (term approximate to 148 d). In 10 lambs born at term , respiratory function was studied four times at weekly intervals; a g roup of nine lambs from normal pregnancies served as controls. Over th e 4-wk study period, treated lambs had significantly higher breathing rates and smaller tidal volumes than controls, although the difference s diminished with age. Minute ventilation and O-2 consumption were the same in each group, and when related to body weight, both declined wi th age. Treated lambs were normoxemic but were hypercapnic compared wi th controls for up to 4 wk. Functional residual capacity, measured by helium dilution, was the same in each group and increased with age. St atic compliance of the respiratory system was lower in treated lambs u p to 4 wk; lung compliances were the same in each group, but chest wal l compliance was lower in treated Iambs than in controls for 4 wk. Pos tmortem measurements, at 27-28 d, of pulmonary dry weights, DNA conten ts, and protein contents suggest that the lungs of treated lambs may h ave been mildly hypoplastic. We conclude that oligohydramnios causes a decreased chest wall compliance, which leads to rapid, shallow breath ing and a mild hypercapnia lasting for at least 4 postnatal wk.