Motor control of the palatoglossus and genioglossus during changes in breathing route.

Abstract

High activity of upper airway dilator muscles is thought to be critical in preventing sleep-related upper airway collapse. To date, most of the research regarding upper airway dilator muscles has focused on the genioglossus muscle, which protrudes the tongue and opens the retroglossal airway. However, collapse commonly occurs in the retropalatal region. We therefore aimed to examine the motor control of the palatoglossus muscle as well as investigate breathing route-related changes in genioglossus and palatoglossus motor units. Single motor unit recordings of the genioglossus and palatoglossus were made simultaneously in healthy individuals during wakefulness while breathing through the nose with the mouth closed (NMC), nose with mouth open (NMO) or orally (OMO). The palatoglossus was found to have all 5 motor unit firing patterns that have been observed in other upper airway dilator muscles, but during nasal breathing had a higher proportion of tonically active but inspiratory modulated motor units as compared to the genioglossus (67% vs 30%). When still breathing nasally but with the mouth open, the units with an expiratory firing pattern in genioglossus, and all firing patterns in palatoglossal, increased their firing rates compared to nasal breathing with the mouth closed (GG: 17.8±4.9 vs 23.1±4.8 Hz, PG: 17.0±4.0 vs 19.3±4.0 Hz). Finally, oral breathing resulted in dramatic reductions in the number of palatoglossal motor units that were firing (35 units vs 92 during nasal breathing). Palatoglossus activity may contribute importantly to airway collapsibility and may provide an alternate pathway for preventing sleep-related airway collapse.