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The effects of muscle aging on hyoid motion during swallowing : a study using a 3D biomechanical model Tsou, Ling


The ability to swallow is crucial in maintaining adequate nutrition. However, there is a high prevalence of dysphagia among the elderly and a high associated mortality rate. To study the various causes of the associated physiological changes, one must first understand the biomechanics of normal swallowing. However, functional studies of the anatomically complex head and neck region can prove to be difficult due to both technical and ethical reasons. To overcome the limitations of clinical studies, this thesis proposes the use of a 3D computer model for performing dynamic simulations. A state-of-the-art model of the hyolaryngeal complex was created for simulating swallowing-related motor tasks with a special focus on hyoid excursion since reduced hyoid motion is a major indicator of oropharyngeal dysphagia. The model was constructed using anatomical data for a male cadaver from the Visible Human Project and an open-source dynamic simulation platform, ArtiSynth. Hyoid motion data obtained from videofluoroscopy of subjects performing normal swallowing was applied to the model for inversely simulating the potential muscle activities of the extrinsic laryngeal muscles during hyoid excursion. Within a specific range, the model demonstrated the ability to reproduce realistic hyoid motion for swallowing. Selective usage of suprahyoid muscles was also examined and was found to be possible in achieving adequate hyoid excursion for successful swallows. Finally, this study investigated the relationship between muscle weakening and hyoid range of motion using the hyolaryngeal model. Loss of muscle strength is characteristic of the aging process. Simulation of the maximum hyoid displacement under various muscle conditions confirmed a nonlinear reduction in the hyoid motion range under a linear decline in muscle strength. With an assumed rate of muscle weakening, the proportion of hyoid range reduction was estimated for a person at various ages. The results suggest that severe muscle weakening might be required to reduce hyoid excursion sufficiently to impair swallowing to a significant degree.

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