Fig. 3. Norepinephrine and epinephrine plasma concentrations as well as heart rate and arterial pressure in the awake state, during anesthesia with S (+)-ketamine and during S (+)-ketamine anesthesia with arterial pressure adjusted to awake baseline by infusion of sodium nitroprusside (SNP). Mean ± SD from six volunteers. Arterial pressure and heart rate significantly increased during S (+)-ketamine anesthesia, as did norepinephrine plasma concentrations. Note that at the end of the study, arterial pressure was decreased by sodium nitroprusside during S (+)-ketamine and did not differ from values in awake participants. Moreover, norepinephrine plasma concentration tended to increase further during infusion of sodium nitroprusside, in parallel to a significant increase in muscle sympathetic activity. In contrast, mean epinephrine plasma concentration did not significantly change during anesthesia with S (+)-ketamine. * P < 0.05 versus baseline awake.