Introduction - We hypothesized that nifedipine and sildenafil would have no detrimental effects on placental hemodynamics and gas exchange under fetal hypoxemia.<p> <p>Methods - In 33 chronically instrumented fetal sheep, placental volume blood flow (QPlac) and umbilical artery (UA) vascular impedance were measured by Doppler ultrasonography. Fetal carotid artery blood pressure and blood gas ...