Effects of the bolus volume on hyoid movements in normal individuals

The hyoid bone moves during swallowing due to contraction of suprahyoid muscles, which are critical components of normal swallowing function. It has been reported that the muscle force and shortening velocity decline gradually with age. Reduced hyoid velocities may delay the sealing of the laryngeal vestibule and opening of the cricopharyngeal muscle. We hypothesised that the hyoid velocity could be a factor influencing aspiration. This study evaluated effects of bolus volume changes on the hyoid distance and velocity in normal swallowing. The subjects were 21 healthy young adults. Lateral projection videofluorography was recorded while each subject swallowed 2·5, 5·0, 10 and 20 mL of liquid barium. We evaluated the maximum hyoid distance (Max d), anterior and superior distance (Max ad, Max sd). And, we evaluated the maximum velocity (Max v), anterior and superior velocity (Max av, Max sv). Two-way anova test revealed that Max d, Max ad and Max sd for different bolus volumes are not significantly different. But, two-way anova test showed statistically significant difference in Max v, Max av and Max sv among different bolus volume (P < 0·01). Tukey's test showed that there are significant differences in Max v between 2·5 and 20 mL, 5·0 and 20 mL, 10 and 20 mL, and 2·5 and 10 mL swallowing. And, Tukey's test showed significant differences in Max av and Max sv between 2·5 and 20 mL, 5·0 and 20 mL, and 10 and 20 mL swallowing. It is possible that a larger bolus volume requires greater maximum hyoid velocity. We plan to study hyoid velocity in elderly subjects and in those with dysphagia.