Fig. 6. (  A ) Genioglossus negative pressure reflex. The increase in phasic genioglossus activity in response to negative pharyngeal pressure application was inhibited with increasing isoflurane concentrations. *  P < 0.05 for decreasing genioglossus negative pressure effects with increasing isoflurane dose, and for lower values at 2% isoflurane compared with 1% isoflurane. (  B and  C ) Tonic activity of genioglossus muscle. Data are percent of values measured at 1% isoflurane. (  B ) Nonanesthetized state  versus 1% isoflurane (n = 6). Chronically instrumented rats. Tonic activity of genioglossus muscle was significantly higher under room air compared with anesthesia. *  P < 0.05  versus nonanesthetized rats. (  C ) Dose–response effect of isoflurane. Isoflurane dose-dependently decreased tonic genioglossus activity. Data from 12 rats. *  P < 0.05 for decreasing tonic genioglossus activity with increasing isoflurane dose, and for lower values at 2% isoflurane compared with 1% isoflurane.