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Reproductive Sciences
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Fetal Hypercapnia in High-Altitude Acclimatized Sheep: Cerebral Blood Flow and Cerebral Oxygenation

Takuji Tomimatsu, MD

Jorge Pereyra Pena, MD

Center for Perinatal Biology, Departments of Physiology and Obstetrics & Gynecology, School of Medicine, Loma Linda University, Loma Linda, California

Lawrence D. Longo, MD

Center for Perinatal Biology, Departments of Physiology and Obstetrics & Gynecology, School of Medicine, Loma Linda University, Loma Linda, California; llongo{at}llu.edu

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 PO2 (tPO2), and sagittal sinus oxyhemoglobin saturation (HbO2) in response to 20-minute hypercapnia. They also calculated cerebral O2delivery and cerebral fractional O2 extraction. The authors compared these results to those obtained in near-sea-level control animals (low-altitude group). In response to hypercapnia (arterial PCO2 = 63± 2 torr vs 42± 1 torr baseline), high-altitude fetuses showed similar increases in LD-CBF, cortical tPO2, and sagittal sinus (HbO2) as compared with those responses seen in the fetus at low altitude. Nonetheless, these fetuses showed a significantly smaller decrease in cerebral fractional O2 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.

Key Words: Fetal hypercapnia • high altitude • chronic hypoxia • cerebral oxygen metabolism

Reproductive Sciences, Vol. 14, No. 1, 51-58 (2007)
DOI: 10.1177/1933719106298211
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