Fig. 2. Genioglossus activity and flow rate during isoflurane (ED50[median effective dose]) and propofol (ED50). Values are given in microvolts. * P < 0.05 versus isoflurane. A –C : Data from protocol 1 (n = 18). D : Pooled data from protocols 1 and 2 (n = 46). ( A ) Phasic genioglossus activity measured at time of assessment of genioglossus activity. Genioglossus activity was significantly lower during propofol anesthesia compared with isoflurane, and carbon dioxide levels were higher (82 ± 3 vs. 41 ± 1 vs. mmHg; P < 0.05). ( B ) Tonic genioglossus activity. Tonic genioglossus activity was significantly lower during propofol anesthesia compared with isoflurane. ( C ) Flow rate. Flow rate was significantly lower ( P < 0.05) during propofol anesthesia compared with isoflurane. MTA = moving time average. ( D ) Phasic genioglossus activity at ED50(given as rate of MTA rise) as a function of flow rate. Pooled data from protocols 1–3 (n = 53). Flow rate correlated significantly with phasic genioglossus activity. r = 0.47, P < 0.05. Open circles = isoflurane; closed circles = propofol.