Figure 1. Time course of the effects of placebo-oxygen, 15% and 30% end-tidal nitrous oxide, and 0.3% and 0.6% end-tidal sevoflurane on drug-effect strength ratings. Each time point is the mean for 12 volunteers. The scale ranged from 1 (no drug effect) to 5 (strong drug effect). Time 0 refers to baseline measures, times 5 and 15 min refer to intrainhalation testing, and times 40, 65, and 95 min represent postinhalation testing. The vertical dashed line separates the 35-min inhalation period from the recovery period. Asterisks indicate a significant difference from placebo-oxygen.