Tracheal occlusion alters pulmonary circulation in the fetal lamb with normally developing lungs.

Abstract Background Tracheal occlusion (TO) promotes fetal lung growth through an increase in intraluminal pressure. Although evidence suggests that fetal TO (FETO) decreases the occurrence of pulmonary hypertension in severe congenital diaphragmatic hernia, controversies on its effect on the pulmonary circulation remain. Therefore, we investigated the effects of FETO on the lung hemodynamics in a chronically catheterized fetal lamb model. Methods Fifteen pregnant ewes were operated on between 125 and 128days of gestation (term: 145days). Catheters and ultrasonic flow transducer were placed through a left thoracotomy in the lamb fetus to determine aortic, pulmonary and left atrial pressures, and left pulmonary artery blood flow. A balloon was positioned between the carina and vocal cords under fetoscopic control. The animals were assigned to either control ( n =6) or FETO ( n =9) groups. TO was performed by inflating the balloon. We studied the acute effects of temporary (2-h) and prolonged (4-day) TO on basal pulmonary vascular tone and on the pulmonary vascular reactivity to acetylcholine and to increased fetal oxygen tension. Results We found that left pulmonary blood flow (LPA) increased and pulmonary vascular resistance (PVR) decreased by 20% during brief TO ( p p 2 were blunted during TO. Conclusions These data indicate that antenatal tracheal occlusion promotes active pulmonary vasodilation, which is partly blunted by the mechanical effects of elevation of the intraluminal pressure.