Regional blood flow change in the lamb during the perinatal period

Regional blood flow distribution was studied with a radioactive-labeled microsphere technique in 11 unanesthetized fetal sheep (139 to 143 days' gestation). After cesarean delivery each neonatal lamb was studied at 2 and 24 hours of age. Blood flow to the cerebral hemispheres and adrenal glands decreased progressively after birth and correlated inversely with the postnatal rise in arterial oxygen content ( r = -0.77, p < 0.001 and r = -0.52, p < 0.01, respectively). Blood flow to the gastrointestinal tract and kidneys changed little despite the known increase in blood flow from the late fetal to the early neonatal period. Skeletal muscle and brown fat blood flow were both increased when measured at 2 hours after birth, with an even greater increase in their respective oxygen deliveries presumably reflecting their increased metabolic activity with thermogenesis at this time. Variable blood flow changes are thus evident over the immediate perinatal period. In some cases these changes reflect birth-related changes in either blood gases or functional activity whereas in others the changes simply reflect a continuum from the late fetal to the early neonatal period.