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A narrative review of current functional assessment of the upper esophageal sphincter

: Swallowing is a physiological process organized in a sequence of events grouped in extraesophageal and esophageal phase. Changes in the swallowing mechanism can be seen in many clinical situations. Difficulties in the study of the extraesophageal phase of this mechanism occur frequently due to the velocity of this moment, compared to the esophageal phase, as well as the structural characteristics of the upper esophageal sphincter (UES). The aim of this paper is to make a literature review on current functional assessment of the UES. The authors conducted a PubMed search of research published between August 2009 and December 2020, looking for publications related to the topic studied. All diagnostic methods (imaging and endoscopic), as well as conventional manometry, present technical difficulties for their performance and interpretation of results. The emergence of high-resolution manometry (HRM) brought a great advance in the diagnostic study of the pathophysiological phenomena that affect the UES, as well as the repercussion in this location of other esophageal disorders. Functional study of UES through HRM has allowed not only a better understanding of its functioning under normal and pathological conditions, but also an increased number of situations in which it can be applied.