Effect of Bolus Volume on Upper Esophageal Sphincter Opening: Kinematic Analysis Using 320-Area Detector Computed Tomography

This study aimed to determine the impact of bolus volume on UES opening. Twenty-two healthy subjects (10 males and 12 females, 23–45 years) underwent a CT scan while swallowing 3-, 10-, and 20 ml of thin liquid. Upper esophageal sphincter (UES) cross-sectional area and hyoid and laryngeal displacement were measured at every frame across three conditions. The timing of UES opening onset, UES maximum opening, and duration of UES opening were also measured. With increasing bolus volume, the UES maximum opening area increased, at the UES opening onset, at the UES maximum opening was earlier, and the duration of the UES opening prolonged. The maximum displacement of the hyoid and larynx was significantly more anteriorly and higher with a large bolus volume. However, the hyoid displacement at the timing of UES maximum opening did not change across three bolus volumes. This result suggests that the increase in the UES maximum opening area with increasing bolus volume was modulated by the bolus itself rather than by the hyoid movement.