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.
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Jacob P, Kahrilas PJ, Logemann JA, Shah V, Ha T. Upper esophageal sphincter opening and modulation during swallowing. Gastroenterology. 1989;97:1469–78.
Cook IJ, Dodds WJ, Dantas RO, et al. Opening mechanisms of the human upper esophageal sphincter. Am J Physiol. 1989;257:G748–59.
Kahrilas PJ, Dodds WJ, Dent J, Logemann JA, Shaker R. Upper esophageal sphincter function during deglutition. Gastroenterology. 1988;95:52–62.
Ali G, Wallace KL, Luanda TM, Hunt DR, Decarle DJ, Cook IJ. Predictors of outcome of cricopharyngeal disruption for pharyngeal dysphagia. Dysphagia. 1997;12:133–9.
Cock C, Jones CA, Hammer MJ, Omari TI, McCulloch TM. Modulation of upper esophageal sphincter (UES) relaxation and opening during volume swallowing. Dysphagia. 2017;32:216–24.
Pal A, Williams RB, Cook IJ, Brasseur JG. Intrabolus pressure gradient identifies pathological constriction in the upper esophageal sphincter during flow. Am J Physiol Gastrointest Liver Physiol. 2003;285:G1037–48.
Hewitt GF, Hall-Taylor NS. Regimes of flow. In: Annular two-phase flow. Oxford, New York, 1970:4–20.
Inamoto Y, Saitoh E. Morphologic and kinematic analysis of swallowing using multislice CT. In Dysphagia Diagnosis and Treatment. Springer, 2017:333–349.
Inamoto Y, Saitoh E, Ito Y, Kagaya H, et al. The Mendelsohn maneuver and its effects on swallowing: kinematic analysis in three-dimensions using dynamic area detector CT. Dysphagia. 2018;33:419–30.
Barrett JF, Keat N. Artifacts in CT: recognition and avoidance. RadioGraphics. 2004;24:1679–91.
Patel S, McAuley WJ, Cook MT, Sun Y, Hamdy S, Liu F. The Swallowing characteristics of thickeners, Jellies and yoghurt observed using an in vitro model. Dysphagia. 2019. https://doi.org/10.1007/s00455-019-10074-1.
Ito Y, Inamoto Y, Saitoh E, et al. The effect of bolus consistency on pharyngeal volume during swallowing: kinematic analysis in three dimensions using dynamic area detector CT. J Oral Rehabil. 2020;47:1287–96.
Iida T, Kagaya H, Inamoto Y, et al. Measurement of pharyngo-laryngeal volume during swallowing using 320-row area detector computed tomography. Dysphagia. 2017;32:749–58.
Walczak CC, Jones CA, McCulloch TM. Pharyngeal pressure and timing during bolus transit. Dysphagia. 2007;32:104–14.
Mulheren R, Inamoto Y, Odonkor C, et al. The association of 3D volume and 2D area of post-swallow pharyngeal residue on CT imaging. Dysphagia. 2019;34:665–72.
Ho AK, Inamoto Y, Saitoh E et al. Extracting moving boundaries from dynamic, multislice CT images for fluid simulation. Comput Methods Biomech Biomed Eng Imaging. 2016:1–6.
The authors sincerely appreciate the members of the department of Radiology, Fujita Health University for their assistance and suggestions.
This research was partially supported by JSPS KAKENHI (19K11310).
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All authors declare that they have no conflict of interest.
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Inamoto, Y., Saitoh, E. & Palmer, J.B. Annular Flow in the Upper Esophageal Sphincter Demonstrated with Dynamic 320-row Area Detector Computed Tomography. Dysphagia (2021). https://doi.org/10.1007/s00455-020-10241-9