EFFECTS OF DUCTUS-ARTERIOSUS OCCLUSION ON PULMONARY-ARTERY PRESSURE DURING IN-UTERO VENTILATION IN FETAL SHEEP

Seven fetal sheep were prepared to study the short-term effects of in utero ventilation and ductus arteriosus occlusion on pulmonary artery pressure and on fetal right ventricular function assessed using the ri ght atrial pressure-right ventricular stroke volume relationship. Nine days postsurgery (140 days gestation), blood gas and haemodynamic val ues were obtained before and during in utero ventilation with 100% O-2 , and during ventilation with the ductus arteriosus occluded. Oxygen c ontent increased significantly from 7.2 to 14.5 ml dl(-1) with ventila tion and remained elevated at 14.4 ml dl(-1) with ventilation with the ductus arteriosus occluded. In utero ventilation produced a left to r ight atrial pressure gradient and depression of the right atrial press ure-right ventricular stroke volume relationship. Ductus arteriosus oc clusion during in utero ventilation reduced the left to right atrial p ressure gradient, and along with a decrease in pulmonary artery pressu re, resulted in an upward shift of the right atrial pressure-right ven tricular stroke volume relationship, but only to the preventilation le vel. This study indicates that the fetal right atrial pressure-right v entricular stroke volume relationship is significantly altered, both b y changes in the left to right atrial pressure gradient and by changes in pulmonary artery pressure seen with in utero ventilation and subse quent ductus arterios us occlusion.