Abstract
Aims: This study aimed to clarify the characteristics of pharyngeal swallowing in patients with severe motor and intellectual disabilities (SMID) by comparing hyoid bone movements during swallowing in patients with SMID and healthy adults. Subjects and Method: This study included 24 healthy adults and 24 patients with SMID. We recorded videofluoroscopic images of swallowing (VF) at 30 frames/s as subjects swallowed 3 to 5 mL of food paste. A coordinate plane with the second and fourth cervical vertebrae as the reference line was set and VF animation was analyzed for each frame. For the period from the start of hyoid bone elevation to the maximum elevation, we measured the anterior/superior/total moving distance, movement trajectory, and distance between mandible and hyoid bone. The hyoid bone movement time was linearly transformed for each subject to common time units. Hyoid bone movement was divided into a superior phase and an anterior phase, using the mean lower limit of the 95% confidence interval for healthy adults as the reference value. Those who were below the reference value in the superior phase were classified as the superior phase recession group (SR), and those below the reference value in the anterior phase were classified as the anterior phase stagnation group (AS). The results were compared using one-way analysis of variance (ANOVA). Results and Discussion: The SR group included 12 subjects, with 7 in the AS group. ANOVA with multiple comparisons showed that the anterior movement distance of the hyoid bone was significantly greater in healthy adults than in the SR (p＜0.01) and AS (p＜0.01) groups. The superior movement distance of the hyoid bone was significantly greater in the SR group than in healthy adults (p＜0.01). The distance between the mandible and the hyoid bone was significantly greater in the SR group than in healthy adults (p＜0.01) and the AS group (p＜0.05). It was thought that muscle contraction power decreased due to extension of the ventral suprahyoid muscles in the SR group, and that muscle contraction power decreased due to a decrease in extensibility or to hypotonicity of the infrahyoid muscles in the AS group. Conclusion: Among patients with SMID, the hyoid bone pulled backward in one group when it should have moved upward, and moved an insufficient distance in the other group when it should have moved forward.
