Background and Aims: The oropharyngeal swallow accommodates a range of bolus volumes with substantial impact on its dynamic radiographic appearance despite being a nearly reflexive sequence. The aim of this study was to analyze the mechanism of volume accommodation. Methods: Coordination of the glossopalatal junction, velopharyngeal junction, laryngeal vestibule, and upper esophageal sphincter (UES) and intraluminal pharyngeal dimensions were measured from biplane videofluoroscopic swallowing studies in 8 volunteers during 1- and 20-mL swallows. These measurements were applied to three- dimensional reconstructions of the pharyngeal swallow, permitting analysis of their effect on intraluminal volume and propulsive function. Results: Dividing the pharyngeal swallow into periods of reconfiguration, sustained reconfiguration, and offset of reconfiguration, volume accommodation occurred by a 0.2-second prolongation of reconfiguration, preserving the coordination of the onset and offset events. Augmented reconfiguration increased the dimensions of the pharyngeal chamber, caused more rapid bolus expulsion, and increased UES distention. However, maximal transphincteric flow per unit area across the UES was constant, showing its compliance. Conclusions: Volume accommodation is accomplished by augmenting and prolonging pharyngeal reconfiguration from a respiratory to deglutitive pathway. This modification in the timing of neurally mediated events is amplified by its mechanical consequences, resulting in the different cineradiographic appearance and propulsive attributes of large and small volume swallows.
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