Regional respiratory movement of the tongue is coordinated during wakefulness and is larger in severe obstructive sleep apnoea

Key points Coordination of the neuromuscular compartments of the tongue is critical to maintain airway patency. Currently, little is known about the extent to which regional tongue dilatory motion is coordinated in heathy people and if this coordination is altered in people with obstructive sleep apnoea (OSA). We show that regional tongue muscle coordination in people with and without OSA during wakefulness is associated with effective airway dilatation during inspiration, using dynamic tagged magnetic resonance imaging. The maximal movement of four compartments of the tongue were correlated and occurred concurrently towards the end of inspiration. If tongue movement was observed, people with more severe OSA had larger movement and moved more compartments (up to four) to maintain airway patency, while people without OSA moved only one compartment. These results suggest that airway patency is preserved during wakefulness in people with OSA via active dilatory movement of the genioglossus. Maintaining airway patency when supine requires neural drive to the genioglossus horizontal and oblique neuromuscular compartments (superior fan-like and inferior horizontal genioglossus, regions that are innervated by different branches of the hypoglossal nerve) to be coordinated during breathing, but it is unknown if this coordination is altered in obstructive sleep apnoea (OSA). This study aimed to assess coordination of airway dilatory motion across four mid-sagittal tongue compartments during inspiration (i.e. anterior and posterior of the horizontal and oblique compartments), and compare it in controls and OSA patients. Fifty-four participants (12 women, aged 20-73 years) underwent dynamic 'tagged' magnetic resonance imaging during wakefulness. Ten participants had no OSA [apnoea hypopnoea index (AHI) < 5 events h(-1)], 14 had mild OSA (5 < AHI <= 15 events h(-1)), 12 had moderate OSA (15 < AHI <= 30 events h(-1)) and 18 had severe OSA (AHI > 30 events h(-1)). A higher AHI was associated with a greater anterior movement of the anterior and posterior horizontal compartments (Spearman, r = -0.32, P = 0.02 for both), but not in the oblique compartments. If movement was observed, higher OSA severity was associated with an anterior movement of a greater number of compartments. Controls only moved the posterior horizontal compartment while the anterior horizontal compartment also moved in OSA participants. Oblique compartments moved only in people with severe OSA. The maximal anterior inspiratory movement of the four compartments was highly correlated (Spearman, P < 0.001) and occurred concurrently. The posterior horizontal compartment had the greatest anterior motion. These results suggest that airway patency is preserved during wakefulness in people with OSA via active dilatory movement of the genioglossus.