Figure 6.

Estimated effect of untreated obstructive sleep apnea (OSA) on dynamic ventilatory response to asphyxia, and on arousal threshold, in individual patients. The effect of untreated OSA was assumed to be the opposite of the change observed following CPAP treatment. Ventilatory response to asphyxia is the increase in ventilation (expressed as % of baseline ventilation) during the 5th breath following a change in inspired gas from air to 3% CO₂ in 15% or 11% O₂. Arousal threshold is the increase in chemical drive (expressed as % baseline) that is associated with a 50% probability of arousal (T_A50). Note the wide range of responses among patients and the lack of correlation between the 2 responses.