Response of the Upper Esophageal Sphincter to Esophageal Distension Is Affected by Posture, Velocity, Volume, and Composition of the Infusate

Abstract

Background & Aims Studies of the pressure response of the upper esophageal sphincter (UES) to simulated or spontaneous gastroesophageal reflux have shown conflicting results. These discrepancies could result from uncontrolled influence of variables such as posture, volume, and velocity of distension. We characterized in humans the effects of these variables on UES pressure response to esophageal distension. Methods We studied 12 healthy volunteers (average 27±5 years old, 6 male) using concurrent esophageal infusion and high-resolution manometry to determine UES, lower esophageal sphincter, and intraesophageal pressure values. Reflux events were simulated by distal esophageal injections of room-temperature air and water (5, 10, 20, and 50 ml) in individuals in 3 positions (upright, supine and semi-supine). Frequencies of various UES responses were compared using χ2 analysis. Multinomial logistical regression analysis was used to identify factors that determine the UES response. Results UES contraction and relaxation were the overriding responses to esophageal water and air distension, respectively, in a volume-dependent fashion (P<.001). Water-induced UES contraction and air-induced UES relaxation were the predominant responses among individuals in supine and upright positions, respectively (P<.001). The prevalence of their respective predominant response significantly decreased in the opposite position. Proximal esophageal dp/dt significantly and independently differentiated the UES response to infusion with water or air. Conclusions The UES response to esophageal distension is affected by combined effects of posture (spatial orientation of the esophagus), physical properties, and volume of refluxate, as well as the magnitude and rate of increase in intraesophageal pressure. The UES response to esophageal distension can be predicted using a model that incorporates these factors.

Impaired Upper Esophageal Sphincter Reflexes in Patients With Supraesophageal Reflux Disease

“…Since spontaneous EPR events are relatively infrequent and their composition and occurrence is unpredictable, we adopted the esophageal infusion model with controlled timing and composition of infusate to simulate reflux events in subjects 2 . Studies were conducted in supine position for liquid infusion during which the airway is more vulnerable, and physiologic demand for protective esophago-UES reflexes is greater.…”

“…The infusion port was placed in the distal third of esophagus and the site was confirmed by impedance signature of air injection in the upright position. Air injections were performed in semi-upright position when belching is physiologically more common 2 . Then, subjects were placed in a recumbent position for the remainder of the study protocol, and each infusion was performed when the UES, LES and esophageal pressures were stable at baseline 2 .…”

“…Air injections were performed in semi-upright position when belching is physiologically more common 2 . Then, subjects were placed in a recumbent position for the remainder of the study protocol, and each infusion was performed when the UES, LES and esophageal pressures were stable at baseline 2 . Volunteers were instructed not to suppress their belch or swallow response.…”

“…Reflux of gastric content into the esophagus triggers a number of reflexes involving the upper esophageal sphincter (UES) 1, 2 , and esophageal body 2, 3 . These reflexes serve to protect the pharynx and upper airways from entry of the noxious refluxate into the pharynx, esophagopharyngeal reflux (EPR), and transport the refluxate back into stomach 4 .…”

“…The reasons for inability of prior studies to address this issue may include subject selection (since abnormities may have only been present in a subset of GERD patients), and differences in study technique and recording equipment 9, 12 . Recent studies of both naturally occurring and simulated reflux events in normal subjects have shown that supine posture and slow rate of esophageal pressure rise during esophageal liquid distention significantly increase the frequency of elicitation of esophago-UES contraction reflex (EUCR), and inversely decrease the frequency of elicitation of esophago-UES relaxation reflex (EURR) 2, 13 . The recent development of high-resolution manometry with concurrent intraluminal impedance recording has lead to enhanced spatial pressure monitoring and objective verification of the luminal distribution of esophageal contents.…”