Fig. 3. Effects of isoflurane on genioglossus activity and respiratory function. Data are mean ± SEM. (  A ) Phasic genioglossus activity at different isoflurane concentrations. Repetitive measurements at 1.0% (n = 12), 1.49 ± 0.01 (ED50) (n = 12), and 2% (n = 6) or 2.25% (n = 6) isoflurane. Phasic genioglossus activity increased dose dependently with isoflurane dose but was significantly lower at 2.25%  versus 1.49 ± 0.01 (ED50) (paired  t test). *  P < 0.05 for increase of genioglossus activity with isoflurane dose (linear mixed model). +  P < 0.05  versus 1.49 ± 0.01 (ED50) isoflurane (paired  t  test). (  B ) Flow rate. Flow rate (tidal volume/inspiration time) increased significantly with isoflurane dose. *  P < 0.05 for dose effect (linear mixed model). #  P < 0.05  versus 1.49 ± 0.01 (ED50) isoflurane (paired  t test). (  C ) Increase in flow rate from 1–2% isoflurane  versus increase in genioglossus activity from 1–2% isoflurane. Isoflurane evoked increase in genioglossus activity correlated significantly with evoked increase in flow rate (  r = 0.6,  P < 0.05; n = 35 rats). MTA = moving time average.