Afferent pathways for hypoglossal and phrenic responses to changes in upper airway pressure.

Our purpose was to determine the afferent pathways underlying reflexes by which changes in upper airway pressure induced alterations in hypoglossal and phrenic nerve activities. An isolated upper airway was produced in decerebrate, vagotomized, paralyzed and ventilated cats. Efferent activities of the phrenic and hypoglossal nerves were monitored. Hypoglossal activity significantly increased following pressure changes in the upper airway of -4 to -21 cm H2O; phrenic discharge declined in most trials. Similar alterations of neural activities were induced by positive pressures though changes of +14 to +21 cm H2O were required for significant responses. These changes in hypoglossal and phrenic activities were greatly reduced following bilateral sectionings of the superior laryngeal nerves but were augmented after the pharyngeal branches of the glossopharyngeal nerves were sectioned. Additional bilateral destruction of the trigeminal nerves almost entirely eliminated responses to pressure changes. We conclude that upper airway receptors may serve to maintain patency of the upper airways. These receptors may play a crucial role in promoting release from upper airway obstructions, especially in sleep.