Fig. 5. Acute experiments: Breathing of tracheostomized rats during ketamine (circles ) and propofol (squares ) anesthesia. During ketamine anesthesia, breathing, represented by (A ) respiratory rate, (B ) tidal volume, (C ) minute ventilation, and (D ) flow rate, was augmented compared with propofol. Based on augmented breathing during ketamine anesthesia, (E ) duty-cycle is increased, resulting in (F ) lower end-tidal carbon dioxide values compared with propofol. *P < 0.05 for dose-effect (within anesthetic agent). +P < 0.05 for an interaction effect (between anesthetic agents). #P < 0.05 versus propofol, same effective dose (post hoc test). TI = inspiratory time; Ttot = total respiratory cycle time; Vt = tidal volume.