Influence of Acid Swallows on the Dynamics of the Upper Esophageal Sphincter

Abstract

Mechanisms of the upper esophageal sphincter (UES) when exposed to acid are still incompletely understood. The presented work investigated the reaction of the UES to acid exposure during swallowing. Ten healthy individuals swallowed ten 2 ml neutral water boli of pH 7, followed by 10 swallows each of different levels of acidity (pH 1.8, pH 3 and pH 5). Effects were analyzed by high-resolution manometry (HRM) for the primary parameter Restitution Time, as well as Resting Pressures, maximal, minimal pressures and time intervals. Restitution Times measured mean values of 12.67 s (SD ± 7.03 s) for pH 1.8, pH 7 = 8.69 s (SD ± 2.72 s), pH 3 = 7.56 s (SD ± 2.23 s) and pH 5 = 7.29 s (SD ± 2.55 s), showing prolonged Restitution Times in the UES when exposed to strong bolus acidity. This difference was significant towards the neutral bolus, but also to less acidic boli (pH 5: p = 0.006, pH 3: p = 0.009, pH 7: p = 0.038). Considerable differences of mean values were found for Post-Swallow Maximum and Period of Sphincter Activity. Also, Pre-Swallow Maximum values were found to be highest with the strongest acid. Relaxation Times showed a slight trend of prolongation for the highest bolus acidity. Prolonged Restitution Times may represent a reflexive protective mechanism triggered by receptors in the pharyngeal mucosa or the UES preventing regurgitation of acid into the pharynx and larynx, besides representing ongoing attempts of acid clearance. Exposure to high levels of acidity by a swallowed bolus does influence UES functions during swallowing.

Keywords: Acid; Deglutition; High-resolution manometry; Restitution time; Swallow; Upper esophageal sphincter.

Fig. 1

The time interval of restitution (t_resti) stretching from the arrival of the peristaltic wave in the upper esophageal sphincter (UES) until the UES reaches its Resting Pressure again (x-axis = time, y-axis = pressures per sensor (P) in mmHg)

Fig. 2

Model-based prediction of Restitution Times (indicated by the red line) in a swallow of a neutral bolus (a pH 7) [38] and an acid bolus (b pH 1.8). The green lines indicate the time interval of the Resting Pressure. The maximum pressure curve is shown in yellow. The x-axis shows a relative time in samples and the y-axis as a multi axis denotes the pressure sensors on the catheter (P1–P20) as well as (scaled) pressures in mmHg. Individual sensor pressures are color coded and shown as a contour plot (see bar on the right) [38]

Fig. 3

a pH-neutral swallow showing restitution patterns [38]. (x = time, y = penetration depth of the catheter, pressures are color coded from blue = 0 to purple = 200 mmHg). b Patterns of restitution in relation with acid swallows (pH 1.8), showing existing “Oscillations” as a prolonged presence of very high pressures

Fig. 3

a pH-neutral swallow showing restitution patterns [38]. (x = time, y = penetration depth of the catheter, pressures are color coded from blue = 0 to purple = 200 mmHg). b Patterns of restitution in relation with acid swallows (pH 1.8), showing existing “Oscillations” as a prolonged presence of very high pressures

Fig. 4

Mean Restitution Times (t_resti) in seconds (y-axis) for boli of different pH-consistencies (x-axis) with p-values for statistical comparisons

Fig. 5

Box plot of Restitution Times (t_resti) in seconds (y-axis) for each pH-value (x-axis)

Fig. 6

Distribution of Oscillations (y-axis) across pH-concentrations (x-axis). White marks swallows where no Oscillation occurred and gray the swallows that showed Oscillations