Effect of surface electrical stimulation of suprahyoid muscles on hyolaryngeal movement

Objective.  This study aims to investigate the movements of hyolaryngeal structures during the surface electrical stimulation of suprahyoid muscles and to compare these with movements during liquid swallowing. Materials and methods.  Twelve volunteers without dysphagia participated in this study. Volunteers swallowed 5 mL of diluted barium liquid, which was recorded videofluoroscopically. They then received surface electrical stimulation at midpoints between the chin and the bilateral edges of the hyoid, and movements were again recorded. Two-dimensional motion analysis was performed and displacements of the hyoid and of subglottic air-column and epiglottic rotations were calculated. Movements caused by surface stimulation were compared to those during liquid swallowing. Results.  Elevation and anterior excursion of the hyoid by electrical stimulation were 66.8% and 45.2% of those during liquid swallowing, respectively, and rotation of the epiglottis by electrical stimulation was 24.0% of that during liquid swallowing. Elevation and anterior excursion of the subglottic air column during liquid swallowing were 24.1 mm and 4.6 mm, respectively, compared with 9.6 mm and 1.9 mm during electrical stimulation. All the movements during electrical stimulation were significantly smaller than those that occurred during liquid swallowing (p < 0.05). Trajectories of the hyoid and larynx during electrical stimulation were smaller than but similar to those that occurred during liquid swallowing. Conclusion.  This study suggests that surface electrical stimulation of suprahyoid muscles causes the elevation and anterior excursion of hyolaryngeal structures, as is observed during normal physiologic swallowing, although the movements involved were smaller. Further studies are required to determine the effect of synchronized electrical stimulation on dysphagia patients with reduced laryngeal elevation to allow the development of a swallow-assisting neural orthosis.