Effects of continuous positive airway pressure (CPAP) on breathing during wake–sleep transition. During wake and sleep transitions, tidal volume, minute ventilation, and peak inspiratory flow decreased and the magnitude of respiratory depression was smaller during CPAP compared to atmospheric pressure (AP). *Statistically significant main effect of treatment on breathing (P < 0.05). †Statistically significant interaction effect between treatment and sleep stage on breathing (P < 0.05). Data obtained from 31 patients with complete breathing data. NREM2 = non–rapid eye movement sleep stage 2.