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To determine the effects of chronic intrauterine pulmonary hypertension on the perinatal pulmonary circulation, we in- duced chronic elevations of pulmonary artery pressure in 24 late-gestation fetal lambs by maintaining partial compression of the ductus arteriosus with an inflatable vascular occluder. Pulmonary artery pressure was increased from 441 to 623 mmHg for 3-14 d. Although left pulmonary artery blood flow initially increased during acute partial ductus compression, the increase in flow was not sustained during chronic ductus com- pression despite persistent elevations of pulmonary artery pressure (P 8 d increased the wall thickness of small pulmonary arteries (P < 0.001). Compared with controls, hypertensive animals had higher pulmonary artery pressure, lower pulmonary blood flow, and predominant right-to-left ductus shunting after cesarean-section delivery (P < 0.0001). We conclude that chronic pulmonary hypertension in utero, in the absence of hypoxemia or sustained increases in blood flow, causes abnormal fetal pulmonary vasoreactivity, structural re- modeling, and the failure to achieve the normal decline in pulmonary resistance at birth.
Abman et al. (Thu,) studied this question.