Alterations in cerebral blood flow and phosphorylated metabolites in piglets during and after partial ischemia

Ventilated piglets were studied before, during (15 min), and after (90 min) hemorrhagic hypotension to correlate a 60% reduction in cerebral blood flow with cerebral energy state using radiolabeled microspheres (n = 12) and in vivo 31P nuclear magnetic resonance spectroscopy (n = 11). Cerebral blood flow (ml.min-1.100 g-1) decreased during hypotension (98 +/- 28 to 41 +/- 28, p less than 0.05), increased at 5 min postreperfusion (131 +/- 53, p less than 0.05), and returned to control values by 90 min postreperfusion. Cerebral O2 uptake was reduced during partial ischemia, remained depressed 5 min postreperfusion, and increased to within 20% of control values at 90 min postreperfusion. Relative to control, hypotension was associated with decreased (p less than 0.05) phosphocreatine (62 +/- 11%), phosphocreatine/inorganic phosphate ratio (41 +/- 10%), and nucleoside triphosphate (82 +/- 12%) while inorganic phosphate increased (155 +/- 32%, p less than 0.05). During ischemia intracellular pH dropped from 7.06 +/- 0.07 to 6.59 +/- 0.31 (p less than 0.05) and the cerebral arteriovenous difference of glucose increased. Phosphorylated metabolites returned to within 10% of control 15 min after blood reinfusion and remained constant thereafter. Based on calculations of ATP synthesis and utilization rates during control and hypotension, we speculate that the rate of energy utilization of the brain during ischemia is reduced 18-49% relative to the control utilization rate.