Influences of airflow in the upper airway upon phasic hypoglossal and phrenic activities: Afferent pathways

The purpose of the present study was to examine the afferent mechanisms for phasic hypoglossal and phrenic responses to airflow chagnes in the upper airway (UAW). An isolated UAW was produced in decerebrate, unanesthetized, vagotomized, paralyzed and ventilated cats. Activities of both the hypoglossal and phrenic nerves were monitored at hyperoxic (FETCO₂ > 0.80) normocapnia (FETCO₂ = 0.04-0.05). As inspiratory airflow passing through the UAW, hypoglossal activity enhanced significantly while phrenic discharge reduced (p < 0.01). After bilateral denervation of the superior laryngeal nerve (SLN), enhancements of hypoglossal activity in response to the same level of airflow were much lower whereas reduce in phrenic discharge was eliminated. Combined with sectioning of the glossopharyngeal nerve (GPN), augmentation of hypoglossal response to airflow was even higher. This increase in hypoglossal activity with airflow changes was not discerned when the trigeminal ganglion (TGG) was further destroyed. These results suggest that airflow changes in the UAW, which was sensed by the receptors in the SLN, GPN, and TGG, produce an increase in hypoglossal discharge and a decrease in phrenic burst. Increase in hypoglossal activity in response to airflow change in the UAW may relate to keeping a patent UAW.