Arousal from Sleep Does Not Lead to Reduced Dilator Muscle Activity or Elevated Upper Airway Resistance on Return to Sleep in Healthy Individuals

Study Objectives: To compare changes in end-tidal CO2, genioglossus muscle activity and upper airway resistance following tone-induced arousal and the return to sleep in healthy individuals with small and large ventilatory responses to arousal. Design: Observational study. Setting: Two sleep physiology laboratories. Patients or Participants: 35 men and 25 women with no medical or sleep disorders. Interventions: Auditory tones to induce 3-s to 15-s cortical arousals from sleep. Measurements and Results: During arousal from sleep, subjects with large ventilatory responses to arousal had higher ventilation (by analytical design) and tidal volume, and more marked reductions in the partial pressure of end-tidal CO2 compared to subjects with small ventilatory responses to arousal. However, following the return to sleep, ventilation, genioglossus muscle activity, and upper airway resistance did not differ between high and low ventilatory response groups (Breath 1 on return to sleep: ventilation 6.7 +/- 0.4 and 5.5 +/- 0.3 L/min, peak genioglossus activity 3.4% +/- 1.0% and 4.8% +/- 1.0% maximum, upper airway resistance 4.7 +/- 0.7 and 5.5 +/- 1.0 cm H2O/L/ s, respectively). Furthermore, dilator muscle activity did not fall below the pre-arousal sleeping level and upper airway resistance did not rise above the pre-arousal sleeping level in either group for 10 breaths following the return to sleep. Conclusions: Regardless of the magnitude of the ventilatory response to arousal from sleep and subsequent reduction in PETCO2, healthy individuals did not develop reduced dilator muscle activity nor increased upper airway resistance, indicative of partial airway collapse, on the return to sleep. These findings challenge the commonly stated notion that arousals predispose to upper airway obstruction.