Baroreflex control of heart rate in man awake and during enflurane and enflurane--nitrous oxide anesthesia

Baroreflex control of heart rate was assessed by means of a pressor test in two groups of subjects while awake and at two levels of anesthesia with enflurane (Group I) and enflurane-nitrous oxide (Group II). In the awake control situation, calculated mean slopes (+/- SD) were 23 +/- 8 (Group I) and 25 +/- 11 (Group II). There was no significant difference between the groups. During enflurane anesthesia (Group I) mean slopes were significantly depressed to 5 +/- 5 at 1 MAC and 6 +/- 6 at 0.8 MAC. During enflurane-nitrous oxide anesthesia (Group II), slopes were significantly depressed to 5 +/- 3 at 1 MAC and 6 +/- 4 at 0.9 MAC. There was no significant difference between the extents of depression in the two groups. It is concluded that both enflurane anesthesia and enflurane-nitrous oxide anesthesia at 1 MAC produce significant depression of baroreflex control of heart rate in man.