Fig. 4.

The appearance and characteristics of periodic breathing during baseline recording on room air in non-REM and REM sleep. Most periodic breathing episodes occurred during non-REM sleep and represented a state of increased ventilation compared with non-REM periods of stable breathing. The median EtCO₂ was systematically lower in non-REM sleep during periodic breathing than during stable breathing. Base, baseline PSG results on room air; EtCO₂, end-tidal carbon dioxide content of exhaled air; nR, non-REM sleep; O₂, PSG results on supplemental oxygen; PB, periodic breathing; R, REM sleep.