Recent knowledge on the pathogenesis of sleep apnea reveals that a low respiratory activation threshold (easily awakened) is important for many patients. As most patients experience stable periods of breathing mediated by activation of the upper airway dilator muscle through accumulation of respiratory stimuli, premature awakening can prevent accumulation of respiratory stimuli as well as the resulting stabilization of sleep and breathing. The objective of the present physiological study was to determine the effects of a non-benzodiazepine sedative, eszopiclone, on arousal threshold and AHI (apnea / hypopnea index) in patients with obstructive sleep apnea.