Fig. 7. ( A ) Muscle sympathetic activity (MSA) burst incidence in the awake state, during ketamine anesthesia, and during ketamine anesthesia with arterial pressure adjusted to baseline by infusion of sodium nitroprusside infusion (SNP). Mean ± SD from six healthy subjects. MSA markedly and significantly decreased after induction of anesthesia with ketamine. When arterial pressure was decreased during ketamine anesthesia to awake baseline by SNP, as to inhibit baroreflex afferents, MSA normalized, indicating preserved muscle sympathetic activity during ketamine anesthesia. * P < 0.01 versus baseline awake. ( B ) Relations between diastolic arterial pressure and MSA burst incidence before and after injection of SNP in the awake state and during ketamine anesthesia. Mean ± SD from six healthy subjects. The muscle sympathetic response to hypotensive challenges as indicated by the slope of the regression line was maintained during ketamine anesthesia even at a higher arterial pressure level. Derived from and used with permission from Kienbaum et al. 138