The Effect of Bolus Consistency on Hyoid Velocity in Healthy Swallowing

The aim of this study was to determine whether measures of hyoid velocity increase when swallowing liquids of thicker consistency at a constant volume. A gender-balanced sample of 20 healthy young participants (mean age 31.5) each swallowed 3 boluses of 5 ml volume in 3 consistencies (ultrathin, thin, and nectar-thick barium). Using frame-by-frame tracking of hyoid position, we identified the onset and peak of the hyoid movement and derived measures of velocity (i.e., distance in anatomically normalized units, i.e., % of the C2-4 vertebral distance, divided by duration in ms) for the X, Y, and XY movement directions. Peak hyoid velocity was also identified for each movement direction. Where significant differences were identified, the component measures of hyoid movement distance and duration were further explored to determine the strategies used to alter velocity. The results showed increased velocities and higher peak velocities with the nectar-thick stimuli compared to thin and ultrathin stimuli. This was achieved by a primary strategy of larger hyoid movement distances per unit of time when swallowing nectar-thick liquids. These results point to one mechanism by which thickened liquids may contribute to improved airway protection by facilitating more timely laryngeal vestibule closure.