Neurophysiologic tongue protrusion characteristics$ in obstructive sleep apnea: A comparative study

The essential role of upper airway muscles in maintaining patency has led to the hypothesis that alterations in tongue muscle properties may contribute to the development of obstructive sleep apnea (OSA). Prior studies comparing the mechanical characteristics of tongue muscles in OSA patients and healthy controls have yielded inconsistent results. In this study, we evaluated tongue muscle mechanics using an objective, non-volitional method: surface electrical stimulation of the genioglossus (GG) muscle. Tongue protrusion force, whether generated volitionally or by electrical stimulation, was significantly lower in OSA patients. Stimulated force was consistently lower than volitional force across all participants; however, the two measures were strongly correlated (r = 0.62, p < 0.001). Tongue muscle fatigability in OSA patients did not differ significantly from controls during volitional testing or low-frequency stimulation but was increased during high-frequency stimulation. Twitch contraction and half-relaxation times, as well as high-to-low frequency force curves, were comparable between OSA and control subjects. These findings indicate that although tongue muscle fiber composition appears similar in OSA and control groups, maximal tongue protrusion force is reduced in OSA. Given the inconsistent results of prior studies, we suggest that the methodology of force assessment may be critical: different testing modes likely recruit distinct patterns of tongue muscle coordination and may uncover coordination deficits in OSA. Furthermore, the increased fatigability observed during high-frequency stimulation is consistent with the presence of tongue muscle neuropathy in this population.