In obstructive sleep apnea (OSA), the upper airway recurrently closes during sleep. The mechanisms that lead to airway closure are not completely understood. Some studies have shown that there is progressive narrowing of the pharyngeal airway across breaths during expiration (Progressive Expiratory Narrowing, PEN) preceding an obstructive apnea. The cause of PEN is unknown. The investigators will test if lung volumes and low respiratory drive play a role in PEN.

The mechanisms that lead to airway closure in OSA are not completely understood. Some studies have shown that there is progressive narrowing of the pharyngeal airway across breaths during expiration (Progressive Expiratory Narrowing, PEN) preceding an obstructive apnea.

The investigators will test if lung volumes and low respiratory drive play a role in PEN. To this end, the investigators will visualize the pharynx of sleep apnea patients during sleep using a thin endoscope during sleep while simultaneously measuring lung volumes, genioglossus electromyogram, and pharyngeal pressure during flow-limited breaths. Flow limitation will be induced by sustained reductions of continuous positive airway pressure (CPAP).

Inclusion Criteria:

• Normal subjects or patients with OSA

Exclusion Criteria:

• Any unstable cardiac condition (other than well controlled hypertension) or pulmonary problems.
• Any medication known to influence breathing, sleep/arousal or muscle physiology
• Concurrent sleep disorders (insomnia, narcolepsy, central sleep apnea or parasomnia)
• Claustrophobia
• Inability to sleep supine
• Allergy to lidocaine or oxymetazoline hydroclhoride
• For women: Pregnancy