Figure 6. Diaphragmatic activity in REM sleep at different levels of CO₂.

Plotted data are means obtained in separate REM periods in two subjects shown as ♦ and ⋄, respectively. The abscissa is the difference between eupnoeic end-tidal CO₂ levels in NREM sleep and end-tidal CO₂ level during mechanical ventilation in REM sleep. Regression lines for each of the data sets are plotted with exclusion of data enclosed by the ovals.