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

• Published in: Reproductive sciences (Thousand Oaks, Calif.) Calif.), 2007-01, Vol.14 (1), p.51-58
• Main Authors: Tomimatsu, Takuji, Peňa, Jorge Pereyra, Longo, Lawrence D.
• Format: Article
• Language: English
• Subjects: Acclimatization; Altitude; Animals; Carbon Dioxide - blood; Cerebrovascular Circulation - physiology; Female; Fetal Diseases - etiology; Gestational Age; Hypercapnia - etiology; Hypercapnia - physiopathology; Oxygen - blood; Partial Pressure; Pregnancy; Sheep
• ISSN: 1933-7191; 1933-7205
• DOI: 10.1177/1933719106298211

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.