Relating cerebral ischemia and hypoxia to insult intensity.

The contributions of five variables believed to influence the brain's metabolism of O2 during hypoxia [duration, PaO2, delta CMRO2 (the difference between normal and experimental oxygen uptake), O2 availability (blood O2 content.CBF), and O2 deficit (delta CMRO2.duration)] were assessed by stepwise and multiple linear regression. Levels of brain tissue carbohydrates (lactate, glucose, and glycogen) and energy metabolites [ATP, AMP, and creatine phosphate (CrP)] were significantly influenced by O2 deficit during hypoxia, as was final CMRO2. After 60 min of reoxygenation, levels of tissue lactate, glucose, ATP, and AMP were related statistically to the O2 deficit during hypoxia; however, CMRO2 changes were always associated more significantly with O2 availability during hypoxia. Creatine (Cr) and CrP levels in the brain following reoxygenation were correlated more to delta CMRO2 during hypoxia. Changes in some brain carbohydrate (lactate and glucose), energy metabolite (ATP and AMP) levels, and [H+]i induced by complete ischemia were also influenced by O2 deficit. After 60 min of postischemic reoxygenation, brain carbohydrate (lactate, glucose, and glycogen) and energy metabolite (ATP, AMP, CrP, and Cr) correlated with O2 deficit during ischemia. We conclude that "O2 deficit" is an excellent gauge of insult intensity which is related to observed changes in nearly two-thirds of the brain metabolites we studied during and following hypoxia and ischemia.