Background: Conventional radiographic techniques image only the silhouettes of the deglutitive pharyngeal chamber. This study aimed to accurately image the horizontal plane shape and content of the pharynx during swallowing. Methods: Dynamic computerized tomography images of the pharynx were obtained at the rate of 17 per second during swallowing. Multiple adjacent levels were imaged in eight subjects and a single level was scanned in four subjects during swallows of varied volume. Images were analyzed for area, volume, and the bolus fraction of the deglutitive pharyngeal chamber. Results: The deglutitive chamber enlarged to approximately 24 mL (during tongue loading) compared with a preswallow pharyngeal volume averaging 15 mL. Throughout the 10 mL swallows, the bolus occupied less than 30% of the lumen regardless of axial level. The bolus fraction of the deglutitive chamber increased with swallow volume, as did the dimensions of the upper esophageal sphincter and the bolus velocity through the upper esophageal sphincter. Conclusions: The deglutitive pharyngeal chamber was typically approximately 15 mL > the bolus volume, implying that an obligatory 15 mL of air was swallowed under these test conditions. Most swallowed air originated as air trapped within the pharynx and larynx as the oropharynx was sealed from above and below.
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