Figure 3.

Relation between the partial pressure of end tidal CO₂ (P_ETCO₂) measured under resting, baseline conditions and the obstructive apnea-hypopnea index (OAHI). The top panel represents data from all subjects, and the bottom panel shows that the relation is strengthened when the outlier with the very high OAHI is removed from the data set (see Text for details). Measurements were made while the subjects respired room air, and after they were given several minutes to become accustomed to the breathing mask and associated measurement equipment.