To determine the acute effects of increased pulmonary artery pressure and flow on the fetal pulmonary circulation, we studied the response of pulmonary blood flow and vascular reactivity to partial compression of the ductus arteriosus in 22 chronically prepared late-gestation fetal lambs. An inflatable occluder was placed loosely around the ductus arteriosus for compression. Partial compression of the ductus rapidly increased mean pulmonary artery pressure from 45 +/- 1 to 60 +/- 1 mmHg (mean +/- SE) and left pulmonary artery blood flow from 65 +/- 6 to 151 +/- 11 ml/min at 30 min (P less than 0.001; 12 animals). Despite keeping pulmonary artery pressure constant, pulmonary blood flow steadily declined and by 2 h was not different from base-line values. Pulmonary vascular resistance initially fell during the first 30 min of partial compression but then steadily increased and remained elevated above base-line values for at least 30 min after the release of the occluder (P less than 0.001). The decline of pulmonary vascular resistance during the first 30 min of compression was blunted after treatment with the cyclooxygenase inhibitor, meclofenamate (P less than 0.001; 6 animals). Rapid incremental ductus compressions demonstrated a decrease in the slope of the pressure-flow relationship from 3.30 +/- 0.27 (control) to 1.59 +/- 0.21 ml.min-1.mmHg-1 during the postcompression period (P less than 0.001; 12 animals). The vasodilation response to small increases of fetal PO2 was markedly blunted during the postcompression period (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Acute Effects of Hypoxic Gas Admixtures on Pulmonary Blood Flow and Regional Oxygenation in Children Awaiting Norwood Palliation
