Co-activation of tongue protrudor and retractor muscles and the control of pharyngeal airway patency

The hypothesis that pharyngeal airway patency is improved by coactivation of the muscles that protrude and retract the tongue (genioglossus and hyoglossus/styloglossus muscles, respectively) is the focus of the presentation. The conceptual model is that co-contraction during inspiration stiffens the tongue as the antagonist muscles work against one another, thereby minimizing backward displacement of the tongue and subsequent occlusion of the pharynx. The following observations provide support for this conceptual framework: 1) retractor and protrudor muscles respond in parallel to stimulation of chemoreceptors and pulmonary stretch receptors in anesthetized animal models; 2) coactivation evoked by stimulation of the main trunk of the hypoglossal nerve improves inspiratory airflow in human subjects with obstructive sleep apnea, in spite of net tongue retraction; 3) more negative intraluminal pressures are required to cause flow limitation in the isolated pharyngeal airway of the rat when the tongue muscles are co-activated, compared to when the genioglossus muscle is activated selectively. These observations suggest that the tongue retractor muscles play an important but hitherto unforeseen role in the control of pharyngeal airway patency.