Opening mechanisms of the human upper esophageal sphincter

TLDR

The study aimed to characterize the mechanisms of upper esophageal sphincter opening during swallowing and to describe how fluid flow dynamics change with bolus volume. This was achieved by performing simultaneous videofluorography and manometry on 15 healthy volunteers swallowing 2–30 mL of barium. Results showed that UES relaxation and anterior hyoid traction precede opening, that UES diameter, cross‑sectional area, flow duration, and trans‑sphincteric flow rate increase with bolus volume while intrabolus pressure remains below 10 mmHg up to 10 mL, indicating volume‑dependent adaptive changes that allow large boluses to pass with minimal pressure increase and suggesting a sensory feedback mechanism modulating swallow timing.

Abstract

Our goals in this study were to evaluate the mechanisms operative in swallow-associated opening of the upper esophageal sphincter (UES) and to determine the dynamics of fluid flow across the sphincter. For this purpose, we obtained concurrent videofluorographic and manometric studies of 2- to 30-ml barium swallows in 15 normal subjects. We found that the resting UES high-pressure zone corresponded closely with the location of the cricopharyngeus. The findings indicated that manometric UES relaxation and anterior hyoid traction on the larynx invariably preceded UES opening. With graded increases in bolus volume, progressive increases occurred in UES diameter, cross-sectional area, flow duration, and transsphincteric flow rate. Intrabolus pressure upstream to the UES and within the UES at its opening during transsphincteric flow of barium remained within a narrow physiological range of less than 10 mmHg up to a bolus volume of 10 ml. With increases in bolus volume, anterior hyoid movement, UES relaxation, and UES opening occurred sooner in the swallow sequence to accommodate the early entry of large boluses into the pharynx. We conclude that during swallowing 1) normal UES opening involves sphincter relaxation, anterior laryngeal traction, and intrabolus pressure, 2) volume-dependent adaptive changes in UES dimension accommodate large bolus volumes and flow rates with minimal requirement for increases in upstream, or intrasphincteric, intrabolus pressure or UES opening duration, and 3) volume-dependent changes in UES dimensions as well as timing of UES relaxation and opening indicate a sensory feedback mechanism that modulates some components of the swallow response generated by the brain stem swallow centers.