Effect of hypercapnia on the arousal response to airway occlusion during sleep in normal subjects

The effect of an acute increase in PCO2 on the arousal response to occlusion of a mask covering the nose with the mouth sealed during non-rapid-eye-movement sleep was studied in six normal males aged 28.3 +/- 8.3 (SD) yr. Baseline occlusions, while subjects breathed a room air-O2 mixture adjusted to produce an arterial O2 saturation of 98%, were alternated with hypercapnic occlusions in which a small amount of 100% CO2 was added to increase the preocclusion end-tidal PCO2 by 3.5 +/- 0.59 Torr above the baseline value. The maximum deflections in supraglottic airway pressure (Pmax) were measured on the initial occluded breath (PmaxI) and the final breath preceding arousal (PmaxF). In the hypercapnic occlusions, the time to arousal was shorter (23.7 +/- 13.9 vs. 35.2 +/- 15.9 s, P < 0.03) and PmaxI and rate of change in Pmax were higher. However, the PmaxF in the baseline (20.2 +/- 4.1 cmH2O) and hypercapnic occlusions (20.4 +/- 4.4 cmH2O) did not differ. We conclude that an increase in PCO2 before airway occlusion shortens the time to arousal by increasing the initial occluded inspiratory effort (suction pressure) and the rate of increase in effort but does not change the arousal threshold.