How tongue muscles influence upper airway function

To determine how tongue muscles influence upper airway function, we selectively denervated and electrically stimulated these muscles in the isolated feline upper airway and in a sleeping apneic human, respectively. Upper airway pressure-flow relationships were analyzed during periods of inspiratory airflow limitation to determine responses in maximal inspiratory airflow (V̇_Imax) and the pharyngeal critical pressure (Peril). In the isolated feline upper airway, hypercapnea (10% F₁CO₂) was utilized to induce generalized activation of the pharyngeal musculature and compared to hypocapnia (1.3% F₁CO₂) before and after bilateral transection of the cervical strap muscles and the hypoglossal nerves. We observed a significant increase in V̇_Imax and decrease in Pcrit during hypercapnic breathing. These changes were not significantly attenuated by transecting the cervical muscles and hypoglossal nerve. In contrast, electrical stimulation of the hypoglossal nerve in two sleeping apneic patients significantly increased V̇_Imax and decreased Pcrit, although inspiratory airflow limitation persisted. These findings suggest that genioglossal activity can decrease airflow obstruction by decreasing pharyngeal collapsibility, but that this muscle acts in concert with others to modulate upper airway function dynamically.