Affiliation:
1. Department of Physiology, School of Medicine and Biomedical Sciences, State University of New York, Buffalo 14214.
Abstract
Conscious sheep (n = 6), exposed to 3.5 h of normobaric hypoxia (arterial PO2 = 40 Torr) while allowed varying arterial PCO2, showed striking early increments of cerebral blood flow (CBF; +200–250%, by radiolabeled microspheres) and decrements of cerebral vascular resistance (CVR) in association with an early temporary elevation of cerebral O2 consumption (CMRO2; +25–60%). After 2 h, CMRO2 returned to normoxic levels, while CBF declined to a lower but still elevated level (+150%). CBF/CMRO2 increased twofold, while cerebral fractional extraction of O2 was unchanged. Mean arterial pressure was unchanged, but cerebral venous pressure rose (+11 mmHg) in a stable fashion such that cerebral perfusion pressure declined by 13%. Cerebral venous hematocrit and hemoglobin concentration were both elevated (+2.2–2.7% Hct units; +1.0–1.3 g/dl, respectively) above the corresponding arterial values between 150 and 210 min of hypoxia, suggesting venous hemoconcentration in possible association with a transcapillary fluid shift. CBF, and especially CVR, were well correlated with arterial O2 content.
Publisher
American Physiological Society
Subject
Physiology (medical),Physiology
Cited by
21 articles.
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