Fetal hypercapnia in high-altitude acclimatized sheep: cerebral blood flow and cerebral oxygenation.
The authors tested the hypothesis that in the high-altitude acclimatized fetus, hypercapnia has a significantly less effect on cerebral blood flow (CBF) and cerebral oxygenation than that in normoxic sea level controls. In the high-altitude acclimatized fetus (3801 m; maintained from day 30 of gestation to near term; n = 6), by use of a laser Doppler flowmeter with a fluorescent O (2) probe, the authors measured relative CBF (laser Doppler CBF [LD-CBF]), cortical tissue PO(2) (tPO(2)), and sagittal sinus oxyhemoglobin saturation (HbO(2)) in response to 20-minute hypercapnia. They also calculated cerebral O(2)delivery and cerebral fractional O(2) extraction. The authors compared these results to those obtained in near-sea-level control animals (low-altitude group). In response to hypercapnia (arterial PCO(2) = 63+/- 2 torr vs 42+/- 1 torr baseline), high-altitude fetuses showed similar increases in LD-CBF, cortical tPO(2), and sagittal sinus (HbO(2)) as compared with those responses seen in the fetus at low altitude. Nonetheless, these fetuses showed a significantly smaller decrease in cerebral fractional O(2) extraction compared to low-altitude fetuses. In response to hypercapnia in high-altitude, acclimatized, long-term hypoxic fetal sheep, the response of CBF and cerebral oxygenation did not differ significantly from that of low-altitude controls.
Tomimatsu
Takuji
T
Center for Perinatal Biology, Department of Physiology and Obstetrics, School of Medicine, Loma Linda University, Loma Linda, California 92350, USA.
Pena
Jorge Pereyra
JP
Longo
Lawrence D
LD
D000064:Acclimatization; D000531:Altitude; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D005315:Fetal Diseases / Q000209:etiology*; D005865:Gestational Age; D006935:Hypercapnia / Q000209:etiology* / Q000503:physiopathology; D010100:Oxygen / Q000097:blood*; D010313:Partial Pressure; D011247:Pregnancy; D012756:Sheep
D002245:Carbon Dioxide; D010100:Oxygen