Expiratory supraglottic obstruction during muscular relaxation.

Some reports have suggested occurrence of expiratory upper airway narrowing in patients with obstructive sleep apnea (OSA) during sleep and in awake humans during respiratory muscles relaxation. This is compatible with the hypothesis that upper airway muscles are activated during expiration. We studied five healthy volunteers and four patients with OSA in a tank respirator (Emerson; Cambridge, Mass). Supraglottic pressure (Psg) was measured with a catheter with the tip at the retroepiglottic level, tidal volume with an inductance plethysmograph and airflow with a pneumotachograph at the mouth. Diaphragmatic electromyogram was recorded with an esophageal bipolar electrode. Measurements were done at -30 cm H2O. Subjects were asked to breathe in phase with the respirator and then asked to breathe in phase with the respirator and then to relax their muscles. During muscular relaxation, there was supraglottic obstruction and flow limitation. This was observed during both inspiration and expiration. Upper airway obstruction was more severe in patients with OSA than in healthy subjects. In two healthy volunteers, fiberoptic bronchoscopy showed a wide-open oropharyngeal isthmus during active breathing that narrowed during muscular relaxation. This was true during both inspiration and expiration. We conclude that muscular relaxation is associated with upper airway narrowing and flow limitation occurring during both inspiration and expiration. We suggest that to preserve an open upper airway, airway muscles have to be activated during both inspiration and expiration.