Effect of 80% Xe on whole brain blood flow and metabolism in awake monkeys

We previously reported that 33% xenon (Xe) did not activate cerebral blood flow (CBF) and metabolism in monkeys as it appears to do in humans. However, monkeys may be less sensitive to Xe than humans are, which would explain the discrepancy in the results, but no one has studied the effects of higher concentrations of Xe on CBF and metabolism in monkeys. Therefore, we studied the effect of 80% Xe on whole-brain CBF, cerebral metabolic rate for oxygen (CMRO2) and glucose (CMRG) in five awake rhesus monkeys. Platinum microelectrodes and catheters inserted into the torcular Herophili were used to measure H2 clearance CBF, and to withdraw cerebral venous blood for O2 and glucose analysis. Cerebral variables were measured after 15 min exposure to 80% N2/20% O2 followed by 80% Xe/20% O2. Eighty percent Xe compared with 80% N2 increased (p <0.01) CBF by 52.7% from 74 +/- 16 to 113 +/- 25 (mean +/- SD) ml 100 g(-1)/min(-1), CBF/CMRO by 154% from 13 to 33, and decreased (p <0.05) CMRO2 by 39.3% from 6.1 +/- 0.9 to 3.7 +/- 0.8 ml 100 g(-1)/min(-1) and CMRG by 52.4% from 8.4 +/- 2.6 to 4.0 +/- 2.0 mg 100 g(-1)/min(-1). Electroencephalogram frequency decreased from a predominantly alpha to dagger rhythm in three of five monkeys. The 40 and 50% reduction in CMRO2 and CMRG, respectively, by 80% Xe suggests an anesthetic effect at this dose in the rhesus monkey but also activates CBF by 50%.