Effect of ventilatory drive on upper airway patency in humans during NREM sleep.

The pharynx is the site of upper airway obstruction during sleep. As a collapsible tube, pharyngeal patency is determined by transmural pressure and the compliance of the pharyngeal wall. Thus, several factors may influence upper airway patency including the activity of upper airway dilating muscles, the magnitude of caudal traction generated by thoracic inspiratory activity, vascular tone and mucosal surface forces. Changing ventilatory motor output influences upper airway patency primarily by altering dilating muscle activity or caudal traction. Increased ventilatory motor output enhances upper airway patency. Isolated reduction of ventilatory motor output has no significant effect on upper airway patency. However, upper airway narrowing or occlusion occur at the nadir of ventilatory drive during induced periodic breathing and during central apnea. The latter indicates that negative intraluminal pressure is not required for upper airway obstruction during sleep. Therefore, upper airway occlusion during sleep may be due to: (1) passive collapse of a compliant upper airway by gravitational factors or (2) active closure generated by the contraction of the pharyngeal constrictors.