Oxygen delivery to the brain during behavioral activation at acute normobaric hypoxemia

In order to examine the hypothesis that the regional cerebral blood flow (rCBF) is fully regulated to maintain regional cerebral oxygen delivery (rO2-delivery), we reanalyzed quantified positron emission tomography (PET) CBF data obtained in eight healthy subjects. The regional CBF to the hand area was sampled during rest or finger movements, during normoxemia (20%) or acute hypoxemia (8% or 10%), and when acclimatized either to sea level or high altitude (5260 m). Hypoxemia significantly increased the global CBF (gCBF) and rCBF, and decreased the global cerebral oxygen delivery (gO2-delivery), thus the O2-delivery does not entirely regulate CBF. The reduction in rO2-delivery by hypoxemia was significantly larger during high altitude acclimatization than during sea level acclimatization. Acclimatization to high altitude did not significantly change the gCBF or rCBF, while gO2-delivery and rO2-delivery were both significantly increased, however, only during normoxemia. Finger movements significantly increased the rCBF and rO2-delivery to the hand area, while the corresponding global values were unchanged. There were no differences in the rCBF and rO2-delivery increases during finger movements by hypoxemia or acclimatization altitude. This study shows that CBF is not perfectly regulated to maintain O2-delivery in every situation.