Abstract

Understanding bolus flow patterns in swallowing (rheology, the study of flow) is fundamental to assessment and treatment of dysphagia. These patterns are complex and poorly understood. A liquid swallow is typically biphasic, including air, so the actual bolus has both liquid and gas phases. We report a novel observation of annular two-phase flow (a ring of liquid around a core of air) as thin liquids passed through the upper esophageal sphincter (UES). Dynamic CT was performed on 27 healthy asymptomatic volunteers swallowing liquid barium in a semi-reclining position. Each subject swallowed 3, 10, and 20 ml of either thin (14 subjects) or thick liquid (13 subjects). Sagittal and axial images were analyzed. Flow patterns in the UES were assessed on cross-sectional images. Annular flow was seen in the majority of subjects with thin liquid but few with thick liquid swallows. The percentage of Annular flow during UES opening was 3 ml 58%, 10 ml 58%, 20 ml 56% in thin and 3 ml 0%, 10 ml 4%, 20 ml 1% in thick. Annular flow was usually observed from the second or third frames after onset of UES opening. The other pattern, Plug flow was seldom seen with thin but was typical with thick liquid swallows. Annular flow was the most common pattern for thin liquids (but not thick liquids) passing through the UES. Annular flow has been defined as a liquid continuum adjacent to the channel wall with a gas continuum (core) in the center of the channel. The two regions are demarcated by a gas–liquid interface. Annular flow is typical for two-phase gas–liquid flow in a vertical or inclined channel. It results from the interaction of viscosity with cohesive and adhesive forces in the two phases. We infer that the difference in flow pattern between thin liquid–air and thick liquid–air boluses resulted from the differing magnitudes of viscous forces.

Highlights

  • Upper esophageal sphincter (UES) is a complex muscularskeletal-epithelial structure

  • Many studies using manometry reported the importance of assessing intrabolus pressure, which is thought to be a predictor of swallowing dysfunction, bolus flow patterns through upper esophageal sphincter (UES) are little known

  • By the observation of UES cross-section using 3D dynamic computed tomography (CT), a novel finding of flow which is a ring of liquid around a core of air was noted when liquid was passing through the upper esophageal sphincter (UES)

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Summary

Introduction

Upper esophageal sphincter (UES) is a complex muscularskeletal-epithelial structure. It contracts between swallows and relaxes during swallowing. Many studies using manometry reported the importance of assessing intrabolus pressure, which is thought to be a predictor of swallowing dysfunction, bolus flow patterns through UES are little known. This is because most previous studies observed the bolus flow during swallowing using videofluoroscopy, which provides two-dimensional imaging. It reveals lateral and anteroposterior views of bolus movement from oral to esophagus, but not the transverse (cross-sectional superior-inferior) view. We hypothesize that the observed bolus flow patterns in the upper esophageal sphincter are due to the interplay of viscosity with cohesive and adhesive forces

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