Fig. 2. Muscle sympathetic activity (MSA; burst frequency, burst incidence, and total activity) 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. MSA was doubled after induction of anesthesia with S (+)-ketamine both with respect to bursts per time and bursts per 100 heartbeats. Considering the strength of each individual burst by calculating the total activity MSA was almost tripled. When arterial pressure during S (+)-ketamine anesthesia was decreased to awake baseline by sodium nitroprusside, so as to inhibit baroreflex afferents, MSA markedly increased further, that is, beyond the increase observed during anesthesia with S (+)-ketamine alone. * P < 0.05 versus baseline awake; +P < 0.05 versus S (+)-ketamine anesthesia.