Effect of bolus volume on pharyngeal swallowing assessed by high-resolution manometry

Solid-state high-resolution manometry (HRM) is fast becoming the gold standard for studying pharyngeal and esophageal motility. However, very few studies have ever evaluated the effect of bolus volume on the physiology of swallowing using HRM. We aimed to determine the effect of bolus volume on pressure, duration and velocity of the hypopharynx as well as the upper esophageal sphincter during pharyngeal swallowing using HRM. Thirty-four healthy subjects completed nine swallows (3 ml, 5 ml and 10 ml of water, thick liquid, and paste, respectively) in the natural sitting position. Pressure and duration measurements were acquired from the hypopharynx and upper esophageal sphincter (UES) using HRM. The UES residual pressure, UES relaxation duration, maximum preopening UES pressure, maximum postclosure UES pressure, maximum hypopharyngeal pressure, maximum hypopharyngeal pressure rise rate and hypopharyngeal pressure duration were analyzed across bolus volumes using repeated measures of one-way analysis of variance. A significant increase in UES residual pressure associated with increased bolus volume during water and paste swallowing was observed. Furthermore, UES relaxation duration was significantly increased with increasing in bolus volume for all three material swallows. No significant volume effects were found on the hypopharynx. In summary, bolus volume has a significant effect on the residual pressure and relaxation duration, but no effect on maximum preopening pressure or maximum postclosure pressure of the UES. Maximum hypopharyngeal pressure, maximum hypopharyngeal pressure rise rate and pressure duration were also not affected by bolus volume. Consideration of these variables is paramount in understanding normal and pathological swallowing.