Cerebral blood flow response to hypercapnia in immature fetal sheep.
We have reported recently that the cerebral blood flow (CBF) response to isocapnic hypoxic hypoxia is blunted in fetal sheep in utero at 93 days of gestation (term = 145-150 days), a time of rapid brain differentiation in this species. Cerebral O2 transport fell rather than being maintained, as it is in more mature fetuses. The reason for the blunted response was not clear. We hypothesized that the CBF response to hypercapnia also might be blunted. We studied 10 immature fetal sheep in utero at a mean gestational age of 92 days 24 h after catheters were placed into the superior sagittal sinus, axillary artery, and inferior vena cava. We raised the fetal arterial carbon dioxide tension (PaCO2) by changing the mother's inspired PCO2. CBF was measured before and during hypercapnia by the microsphere method. The overall increase in CBF in response to hypercapnia in immature fetuses was lower than in near-term fetuses. However, the difference was eliminated after correcting for differences in cerebral O2 consumption. This study failed to show any defect in the ability of cerebral vessels in immature fetal sheep to respond to carbon dioxide.
Helou
S M
SM
Eudowood Neonatal Pulmonary Division, Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Hudak
M L
ML
Jones
M D
MD
D000818:Animals; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation; D005260:Female; D005318:Fetal Heart / Q000502:physiology* / Q000503:physiopathology; D005333:Fetus / Q000502:physiology*; D006339:Heart Rate; D006935:Hypercapnia / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D010313:Partial Pressure; D011247:Pregnancy; D012756:Sheep
D002245:Carbon Dioxide; D010100:Oxygen