Response of human tongue protrudor and retractors to hypoxia and hypercapnia

It is well established that the genioglossus muscle (tongue protrudor) has a role in protecting or enhancing upper airway patency in individuals with obstructive sleep apnea. However, no investigation completed to date has ad dressed the role of the styloglossus and hyoglossus muscles (tongue retract ors) in maintaining upper airway patency in humans. As a first step toward this goal, the present investigation was designed to examine the response o f human tongue protrudor and retractor muscles during a breathhold maneuver and in steady-state hypoxic hypercapnia. The results showed that the protr udor and retractor muscles were coactivated under both conditions. Measurem ents of onset time of electromyographic activity during steady-state hypoxi c hypercapnia revealed that phasic protrudor and retractor activity was ini tiated immediately before or during the early part of inspiration. We concl ude that the tongue protrudor and retractor muscles are coactivated in resp onse to hypoxia and hypercapnia, and that the tongue retractors may have a significant role in protecting upper airway patency during both apnea and h yperpnea.