Figure 1.

Example showing the effects of lorazepam (1 mg/kg) on arousal threshold and respiratory muscle activities. The traces show the electroencephalogram (EEG), neck electromyogram (EMG), inspired CO₂ level, and the genioglossus (GG) and diaphragm (DIA) muscle activities. The GG and DIA signals are displayed as their moving-time averages (MTA) in arbitrary units (AU). The baseline of the integrator (i.e., electrical zero) is also shown. The arrows on the MTA signals denote an increase in EMG activity. The points of arousal from sleep with vehicle and lorazepam are indicated by the vertical black dashed lines. The time to arousal from the onset of the CO₂ stimuli with vehicle is also superimposed on the lorazepam trace to further highlight the delay in arousal and the corresponding increase in CO₂ level at arousal. Note that GG activity was higher in the presence of lorazepam before arousal from sleep (A₂ vs. A₁), and even at baseline before application of the CO₂ (B₂ vs. B₁). The large increase in GG activity following arousal typically occurred in association with the increased motor activity also observed in the neck, and we did not observe any consistent effect of sedation on that relationship.