Functional Modules of Pharyngeal Swallowing Mechanics

OBJECTIVES: The present retrospective cohort study aims to test the hypothesis that elements of swallowing mechanics including hyoid movement, laryngeal elevation, tongue base retraction, pharyngeal shortening, pharyngeal constriction, and head and neck extension can be grouped into functional modules, and that these modules are predictably altered in disease states. METHODS: Modified barium swallow video clips of a thick and a thin liquid swallow from 40 normal patients and 10 dysphagic post‐treatment oropharyngeal head‐and‐neck cancer (HNC) patients were used in this study. Coordinate locations of 12 anatomical landmarks mapping pharyngeal swallowing mechanics were tracked on every frame during the pharyngeal phase of each swallow using a custom‐made MATLAB tool. Morphometric modularity hypothesis testing was performed on these coordinate data to characterize the modular elements of swallowing function in each cohort using MorphoJ software. RESULTS: The elements of normal swallowing can be grouped into four functional modules including bolus propulsion, pharyngeal shortening, airway protection, and head and neck posture. Modularity in HNC patient showed an intact airway protection module but altered bolus propulsion and pharyngeal shortening modules. To cross‐validate the alteration in modules, a post hoc analysis was performed, which showed significantly increased vallecular (P < .04) and piriform (P < .05) residue but no significant change in aspiration status in the HNC cohort versus controls. CONCLUSIONS: This study suggests that while pharyngeal swallowing mechanics is highly complex, the system is organized into functional modules, and that changes in modularity impacts swallowing performance. This approach to understanding swallowing function may help the patient care team better address swallowing difficulties. LEVEL OF EVIDENCE: 2b