Distension during gastroesophageal reflux: effects of acid inhibition and correlation with symptoms

Why so Many Patients With Dysphagia Have Normal Esophageal Function Testing

Esophageal peristalsis involves a sequential process of initial inhibition (relaxation) and excitation (contraction), both occurring from the cranial to caudal direction. The bolus induces luminal distension during initial inhibition (receptive relaxation) that facilitates smooth propulsion by contraction travelling behind the bolus. Luminal distension during peristalsis in normal subjects exhibits unique characteristics that are influenced by bolus volume, bolus viscosity, and posture, suggesting a potential interaction between distension and contraction. Examining distension-contraction plots in dysphagia patients with normal bolus clearance, ie, high-amplitude esophageal peristaltic contractions, esophagogastric junction outflow obstruction, and functional dysphagia, reveal 2 important findings. Firstly, patients with type 3 achalasia and nonobstructive dysphagia show luminal occlusion distal to the bolus during peristalsis. Secondly, patients with high-amplitude esophageal peristaltic contractions, esophagogastric junction outflow obstruction, and functional dysphagia exhibit a narrow esophageal lumen through which the bolus travels during peristalsis. These findings indicate a relative dynamic obstruction to bolus flow and reduced distensibility of the esophageal wall in patients with several primary esophageal motility disorders. We speculate that the dysphagia sensation experienced by many patients may result from a normal or supernormal contraction wave pushing the bolus against resistance. Integrating representations of distension and contraction, along with objective assessments of flow timing and distensibility, complements the current classification of esophageal motility disorders that are based on the contraction characteristics only. A deeper understanding of the distensibility of the bolus-containing esophageal segment during peristalsis holds promise for the development of innovative medical and surgical therapies to effectively address dysphagia in a substantial number of patients.

Distension-contraction profile of peristalsis in patients with nutcracker esophagus

INTRODUCTION

High amplitude peristaltic esophageal contractions, that is, nutcracker esophagus, were originally described in association with "angina-like pain" of esophageal origin. However, significant number of nutcracker patients also suffer from dysphagia. High-resolution esophageal manometry (HRM) assesses only the contraction phase of peristalsis. The degree of esophageal distension during peristalsis is a surrogate of relaxation and can be measured from the intraluminal esophageal impedance measurements.

AIMS

Determine the amplitude of distension and temporal relationship between distension and contraction during swallow-induced peristalsis in nutcracker patients.

METHODS

HRM impedance (HRMZ) studies were performed and analyzed in 24 nutcracker and 30 normal subjects in the Trendelenburg position. A custom-built software calculated the numerical data of the amplitudes of distension and contraction, the area under the curve (AUC) of distension and contraction, and the temporal relationship between distension and contraction.

RESULTS

In normal subjects, the distension peaks similar to contraction traverse sequentially the esophagus. The amplitude of contraction is greater in the nutcracker esophagus but the amplitude of distension and area under the curve of distension are smaller in patients compared to controls. Distension peaks are aligned closely with contraction in normal subjects, but in patients, the bolus travels faster to the distal esophagus, resulting in a smaller time interval between the onset of swallow and distension peak. Receiver operative characteristics (ROC) curve reveals high sensitivity and specificity of the above parameters in patients.

CONCLUSION

Abnormalities in the distension phase of peristalsis are a possible mechanism of dysphagia in patients with nutcracker esophagus.

Gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GERD) is a common disorder in adults and children. The global prevalence of GERD is high and increasing. Non-erosive reflux disease is the most common phenotype of GERD. Heartburn and regurgitation are considered classic symptoms but GERD may present with various atypical and extra-oesophageal manifestations. The pathophysiology of GERD is multifactorial and different mechanisms may result in GERD symptoms, including gastric composition and motility, anti-reflux barrier, refluxate characteristics, clearance mechanisms, mucosal integrity and symptom perception. In clinical practice, the diagnosis of GERD is commonly established on the basis of response to anti-reflux treatment; however, a more accurate diagnosis requires testing that includes upper gastrointestinal tract endoscopy and reflux monitoring. New techniques and new reflux testing parameters help to better phenotype the condition. In children, the diagnosis of GERD is primarily based on history and physical examination and treatment vary with age. Treatment in adults includes a combination of lifestyle modifications with pharmacological, endoscopic or surgical intervention. In refractory GERD, optimization of proton-pump inhibitor treatment should be attempted before a series of diagnostic tests to assess the patient's phenotype.

Relationship between distension-contraction waveforms during esophageal peristalsis: effect of bolus volume, viscosity, and posture

High-resolution esophageal manometry (HRM) in its current form assesses only the contraction phase of peristalsis. Degree of esophageal distension ahead of contraction is a surrogate of relaxation and can be measured from intraluminal esophageal impedance measurements. The characteristics of esophageal contractions, i.e., their amplitude, duration, velocity, and modulating factors, have been well studied. We studied the effect of bolus volume and viscosity and posture on swallow-induced distension and contraction and the temporal relationship between the two. HRM impedance recordings of 50 healthy subjects with no esophageal symptoms were analyzed. Eight to ten swallows of 5 and 10 mL of 0.5 N saline and a viscous bolus were recorded in the supine and Trendelenburg positions. Custom-built computer software generated the distension-contraction plots and numerical data of the amplitudes of distension (cross-sectional area) and contraction, and the temporal relationship between distension and peak contraction. The hallmarks of distension waveforms are that 1) distension peak, similarly to contraction, travels the esophagus in a peristaltic fashion, and the amplitude of distension increases from the proximal-to-distal direction; 2) the amplitude of distension is greater with 10 mL than with 5 mL and greater in Trendelenburg than in supine posture; and 3) bolus viscosity increases the amplitude of distension and alters the temporal relationship between distension and contraction waveforms. We describe the characteristics of esophageal distension during peristalsis and the relationship between distension and contraction in a relatively large cohort of normal subjects. These data can be used to compare differences between normal subjects and patients with various esophageal motility disorders in future studies.NEW & NOTEWORTHY We studied esophageal distension (surrogate of inhibition) ahead of contraction during peristalsis from intraluminal esophageal impedance measurements. Esophageal distension, similarly to contraction, travels the esophagus in a sequential manner, and the amplitude of esophageal distension increases from proximal to distal direction in the esophagus. Bolus volume, viscosity and posture have significant effects on the amplitude of distension and its temporal relationship with contraction.

Topographical plots of esophageal distension and contraction: effects of posture on esophageal peristalsis and bolus transport

Each swallow induces a wave of inhibition followed by contraction in the esophagus. Unlike contraction, which can easily be measured in humans using high-resolution manometry (HRM), inhibition is difficult to measure. Luminal distension is a surrogate of the esophageal inhibition. The aim of this study was to determine the effect of posture on the temporal and quantitative relationship between distension and contraction along the entire length of the esophagus in normal healthy subjects by using concurrent HRM, HRM impedance (HRMZ), and intraluminal ultrasound (US). Studies were conducted in 15 normal healthy subjects in the supine and Trendelenburg positions. Both manual and automated methods were used to extract quantitative pressure and impedance-derived features from the HRMZ recordings. Topographical plots of distension and contraction were visualized along the entire length of the esophagus. Distension was also measured from the US images during 10-ml swallows at 5 cm above the lower esophageal sphincter. Each swallow was associated with luminal distension followed by contraction, both of which traversed the esophagus in a sequential/peristaltic fashion. Luminal distension (US) and esophageal contraction amplitude were greater in the Trendelenburg compared with the supine position. Length of esophageal breaks (in the transition zone) were reduced in the Trendelenburg position. Change in posture altered the temporal relationship between distension and contraction, and bolus traveled closer to the esophageal contraction in the Trendelenburg position. Topographical contraction-distension plots derived from HRMZ recordings is a novel way to visualize esophageal peristalsis. Future studies should investigate if abnormalities of esophageal distension are the cause of functional dysphagia. NEW & NOTEWORTHY Ascending contraction and descending inhibition are two important components of peristalsis. High-resolution manometry only measures the contraction phase of peristalsis. We measured esophageal distension from intraluminal impedance recordings and developed novel contraction-distension topographical plots to prove that similar to contraction, distension also travels in a peristaltic fashion. Change in posture from the supine to the Trendelenburg position also increased the amplitude of esophageal distension and contraction and altered the temporal relationship between distension and contraction.

Assessment of the Acute Effects of Carbonated Beverage Consumption on Symptoms and Objective Markers of Gastric Reflux

Previous studies have suggested that carbonated beverages may cause gastro-oesophageal reflux. Pepsin (the major enzyme secreted by the stomach) has been suggested to be an objective, acute marker of a reflux event. This pilot study aimed to investigate whether intake of carbonated beverages could affect pepsin concentration in saliva or reflux symptoms. This was assessed by a randomised, crossover trial where participants consumed 330 mL of beverage (carbonated cola, degassed cola or water) at separate visits. Saliva samples and symptom questionnaires were collected at baseline and over the 30 min postprandial period. Pepsin was detected in all saliva samples. No difference was found in the salivary pepsin concentrations between treatments at all time points. There were significantly higher scores (p > 0.05) for feelings of fullness, heartburn, urge to belch and frequency of belches after ingestion of carbonated cola than degassed cola and water. The ingestion of carbonated beverages did not appear to increase postprandial pepsin concentration in saliva compared to other beverages but did evoke higher levels of reflux-related symptoms such as fullness, heartburn and belching. This suggests carbonated beverages may cause symptoms associated with reflux but do not drive detectable levels of gastric juice to reach the oral cavity.

THE ROLE OF THE TRANSDIAPHRAGMATIC PRESSURE GRADIENT IN THE PATHOPHYSIOLOGY OF GASTROESOPHAGEAL REFLUX DISEASE

ABSTRACT Gastroesophageal reflux disease (GERD) is the most common disease of the upper gastrointestinal tract in the Western world. GERD pathophysiology is multifactorial. Different mechanisms may contribute to GERD including an increase in the transdiaphragmatic pressure gradient (TPG). The pathophysiology of GERD linked to TPG is not entirely understood. This review shows that TPG is an important contributor to GERD even when an intact esophagogastric barrier is present in the setting of obesity and pulmonary diseases.

Intra-bolus pressure and esophagogastric gradient, assessed with high-resolution manometry, are associated with acid exposure and proximal migration of refluxate

Trans-sphincteric pressure gradient (TSPG) seems to play a relevant role in eliciting refluxes during transient lower esophageal sphincter relaxations (TLESRs). Intra-bolus pressure (IBP) is considered to be correlated to esophageal wall tone. We aimed to evaluate the relationship between IBP, TSPG during TLESRs and the dynamic properties of refluxate in gastroesophageal reflux disease. Sixteen non-erosive reflux disease (NERD), 10 erosive disease (ERD) patients and 12 healthy volunteers (HVs), underwent 24-hour impedance-pH monitoring and combined high-resolution manometry-impedance before and 60 minutes. After a meal, ERD patients presented a significantly lower mean IBP (4.7 ± 1.6 mmHg) respect to NERD patients (8.9 ± 2.8 mmHg) and HVs (9.2 ± 3.2 mmHg). NERD patients with physiological abnormal acid exposure time showed a mean IBP (10.4 ± 3.1 mmHg) significantly higher than that in NERD with pathological abnormal acid exposure time (5.1 ± 1.5 mmHg). The TSPG value was significantly higher during TLESRs accompanied by reflux than during TLESRs not associated with reflux, both in patients and in HVs. A significant direct correlation was found between IBP, TSPG and proximal spread of refluxes in patients and in HVs. Gastroesophageal reflux disease patients display different degrees of esophageal distension. An increased compliance of the distal esophagus may accommodate larger volumes of refluxate and likely facilitates the injuries development. Higher TSPG values appear to facilitate the occurrence of refluxes during TLESRs. In patients with NERD, higher TSPG and IBP values favor proximal spread of refluxate and hence may play a relevant role in symptom generation.

Refractory gastroesophageal reflux disease

Gastroesophageal reflux disease (GERD) is a condition that develops when the reflux of stomach contents into the esophagus causes troublesome symptoms, esophageal injury, and/or complications. Use of proton pump inhibitors (PPI) remains the standard therapy for GERD and is effective in most patients. Those whose symptoms are refractory to PPIs should be evaluated further and other treatment options should be considered, according to individual patient characteristics. Response to PPIs could be total (no symptoms), partial (residual breakthrough symptoms), or absent (no change in symptoms). Patients experiencing complete response do not usually need further management. Patients with partial response can be treated surgically or by using emerging endoscopic therapies. Patients who exhibit no response to PPI need further evaluation to rule out other causes.

Esophageal function testing: beyond manometry and impedance

Manometry and impedance provide only surrogate information regarding longitudinal wall function and are focused on contractile amplitude and lumen content. Ultrasound imaging provides a unique perspective of esophageal function by providing important information regarding longitudinal muscle contraction. Laser Doppler assessment of perfusion may be an important complementary tool to assess abnormal wall blood perfusion as a possible mechanism of pain.

Esophageal distension during bolus transport: can it be detected by intraluminal impedance recordings?

BACKGROUND

Esophageal multiple intraluminal impedance (MII) measurement has been used to detect gastro-esophageal reflux and bolus transport. It is not clear if MII can detect changes in luminal cross sectional area (CSA) during bolus transport. Intraluminal ultrasound (US) images, MII, and high resolution manometry (HRM) were recorded simultaneously to determine temporal relationship between CSA and impedance during esophageal bolus transport and to define the relationship between peak distension and nadir impedance.

METHODS

Studies were conducted in five healthy subjects. MII, HRM, and US images were recorded 6 cm above LES. Esophageal distensions were studied during swallows and injections of 0.5 N saline bolus into the esophagus.

KEY RESULTS

Temporal change in esophageal CSA correlates with changes in impedance (r-value: mean ± SD = -0.80 ± 0.08, range: -0.94 to -0.66). Drop in impedance during distension occurs as a two-step process; initial large drop associated with onset of CSA increase, followed by a small drop during which majority of the CSA increase occurs. Peak CSA and nadir impedance occur within 1 s of each other. Increase in swallow and injection volumes increased the CSA, had no effect on large drop but increased the small drop amplitude. We observed a significant correlation between peak CSA and nadir impedance (r = -0.90, p < 0.001) and a better correlation between peak CSA and inverse impedance (r = 0.94, p < 0.001).

CONCLUSIONS & INFERENCES

Further studies are needed to confirm that intraluminal impedance recordings may be used to measure luminal CSA during esophageal bolus transport.

Acid sensitization of esophageal mucosal afferents: implication for symptom perception in patients across the gastroesophageal reflux disease spectrum

BACKGROUND

Sensitization of esophageal chemoreceptors, either directly by intermittent acid exposure or indirectly through esophagitis-associated inflammatory mediators, is likely to be the mechanism underlying the perception of heartburn.

AIMS

To compare basal esophageal sensitivity with electrical stimulation and acid, and to compare the degree of acid-induced sensitization in controls and in patient groups across the entire spectrum of gastroesophageal reflux disease: erosive oesophagitis (EO), nonerosive reflux disease (NERD), and functional heartburn (FH).

METHODS

Esophageal sensory and pain thresholds to electrical stimulation were measured before, 30, and 60 minutes after an intraesophageal infusion of saline or HCl. Patients received a 30-minute infusion of 0.15 M HCl and controls were randomized to receive either HCl (n = 11) or saline (n = 10). After electrical sensory threshold testing, participants received another 30-minute infusion of HCl to determine whether sensitivity to acid is increased by prior acid exposure

RESULTS

All patient groups had higher basal sensory thresholds than healthy controls (controls, 13 ± 1.4 mA; FH, 20 ± 5.1 mA; NERD, 21 ± 5.1 mA; EO, 23 ± 5.4 mA; P < 0.05). Acute esophageal acid exposure reduced sensory thresholds to electrical stimulation in FH and NERD patients (P < 0.05). The level of acid sensitivity during the first HCl infusion was comparable between all patient groups and controls. The secondary infusion caused increased discomfort in all participants (P < 0.01). This acid-induced sensitization to HCl was significantly elevated in the patient groups ( P < 0.05).

CONCLUSIONS

(1) Esophageal acid infusion sensitizes it to subsequent electrical and chemical stimulation. (2) The acid-related sensitization is greater in gastroesophageal reflux disease than in controls and may influence in part symptom perception in this population. (3) Acid-related sensitization within the gastroesophageal reflux disease population is not dependant on mucosal inflammation.

Intraluminal ultrasonic probe for volumetric monitoring of liquid gastroesophageal reflux

Methods for volumetric monitoring of liquid gastroesophageal reflux (GER) are still lacking. The aim of this study was to develop an automated intraluminal measurement technique which allows ambulatory volumetric quantification of liquid GER utilizing a minimum-cost intraluminal ultrasonic probe. This probe consists of two 2 MHz ultrasonic crystals longitudinally assembled along a multi-channel intraluminal impedance (MII) catheter. The proposed probe was initially tested with tubular phantoms of different diameters. Measurements of the cross-sectional areas of the phantoms showed high correlation with the actual areas (R(2) = 0.99). Subsequently, two in-vivo human tests were performed. For each human test the catheter assembly was inserted transnasally and the ultrasonic probe was placed in the area of the lower esophageal sphincter. Multiple liquid swallows of different volumes were invoked using electrolyte drinks. Sectional luminal volume (SLV) in the esophagus between the two ultrasonic crystals was obtained. Results of the swallows demonstrated that measured SLVs correlated with the actual swallowed liquid volume. The ultrasonic probe was combined with a MII catheter to discriminate between antegrade and retrograde bolus transit. Increases of SLVs during liquid GER episodes could be utilized to evaluate GER volume in the vicinity of the ultrasonic probe.

Mechanisms of reflux perception in gastroesophageal reflux disease: a review

Patients with reflux symptoms often do not have excessive esophageal acid exposure, and patients with severe gastroesophageal reflux often do not have reflux symptoms. Understanding why different types of reflux induce symptoms in different patients is vital for addressing therapeutic gaps in the treatment of gastroesophageal reflux disease (GERD). Here we review studies providing insight into how gastroesophageal reflux is perceived, with a focus on comparing reflux characteristics and esophageal sensitivity among subgroups of patients with GERD. The available studies indicate that patients with nonerosive reflux disease have fewer acid reflux episodes and thus less esophageal acid exposure than patients with reflux esophagitis but perceive less intense stimuli because of greater esophageal sensitivity. Reflux characteristics other than acidity, such as the presence of bile, pepsin, liquid, or gas in reflux, and the proximal extent or volume of reflux, may also contribute to symptom perception. Factors contributing to greater esophageal sensitivity may include impaired mucosal barrier function, peripherally mediated esophageal sensitivity (enhanced esophageal receptor signaling), and centrally mediated esophageal sensitivity (physiological stressors, sensitization of spinal sensory neurons). Further insight into mechanisms of reflux perception may require a shift toward studies aimed at understanding predisposing cellular, molecular, and genetic factors.

The refluxate: The impact of its magnitude, composition and distribution

The pathogenesis of gastrointestinal reflux disease is multifactoral. Integral to the disease process is the refluxate itself. The characteristics and composition of the refluxate are dependent on several physiological variables. The refluxate may contain varying concentrations of acid, pepsin, gas, or contents of duodenal reflux (such as bile acid and pancreatic enzymes). Characteristics such as volume and proximal extent of the refluxate, and the chemical content of this refluxate can strongly influence the risk of symptom perception. Strong acid (pH<4) and duodeno-gastro-oesophageal reflux are also implicated in the development of mucosal damage in the form of oesophagitis, Barrett's metaplasia and oesophageal adenocarcinoma. The manifestation of disease, however, is not entirely reliant on the refluxate, which must be considered in the context of the genetic, environmental and psychological susceptibility of the individual.

Exercise-provoked esophageal motility disorder in patients with recurrent chest pain

AIM: To investigate the relationship between exercise-provoked esophageal motility disorders and the prognosis for patients with chest pain.

METHODS: The study involved 63 subjects with recurrent angina-like chest pain non-responsive to empirical therapy with proton pump inhibitor (PPI). In all, a coronary artery angiography, panendoscopy, 24-h esophageal pH-metry and manometry, as well as a treadmill stress test with simultaneous esophageal pH-metry and manometry monitoring, were performed. Thirty-five subjects had no significant coronary artery lesions, and 28 had more than 50% coronary artery narrowing. In patients with hypertensive esophageal motility disorders, a calcium antagonist was recommended. The average follow-up period was 977 ± 249 d.

RESULTS: The prevalence of esophageal disorders, such as gastroesophageal reflux or diffuse esophageal spasm, was similar in patients both with and without significant coronary artery narrowing. Exercise prompted esophageal motility disorders, such as a decrease in the percentage of peristaltic and effective contractions and their amplitude, as well as an increase in the percentage of simultaneous and non-effective contractions. In 14 (22%) patients the percentage of simultaneous contractions during the treadmill stress test exceeded the value of 55%. Using Kaplan-Meier analysis and the proportional hazard Cox regression model, it was shown that the administration of a calcium channel antagonist in patients with such an esophageal motility disorder significantly decreased the risk of hospitalization as a result of a suspicion of acute coronary syndrome after the 2.7-year follow-up period.

CONCLUSION: In patients with chest pain non-responsive to PPIs, a diagnosis of exercise-provoked esophageal spasm may have the effect of lowering the risk of the next hospitalization.

Change in cross-sectional area of esophageal muscle does not correlate with the outcome of achalasia after pneumatic balloon dilatation

BACKGROUND AND AIM

Patients with achalasia have a thicker muscularis propria compared to normal patients. Because pneumatic balloon dilatation (PD) is an effective treatment for achalasia, the changes in the esophageal muscles after PD may predict treatment outcomes, if muscular change is of primary importance. In the present study, we aimed to observe the changes in esophageal muscle thickness following PD and assessed whether symptom relapse can be predicted on the basis of the esophageal muscle cross-sectional area (CSA), as measured by high-frequency intraluminal ultrasound (HFIUS).

METHODS

Fifteen patients treated by PD were studied and followed up for a median of 3.6 years. An HFIUS was done before PD and 6 months after PD. The esophageal muscle CSA measured at the lower esophageal sphincter (LES), and 3 and 6 cm above the LES, was used to see whether any association was present between symptom recurrence and the esophageal muscle CSA.

RESULTS

A single PD resulted in a 2-year remission rate of 66%. A significance variance in change (-65%-248%) was noticed in the muscle CSA after PD. The predilation muscle CSA, post-dilation muscle CSA, and change in the muscle CSA after PD was not associated with symptom recurrence.

CONCLUSION

Our findings suggest that measuring the muscle CSA does not help to predict treatment outcome. Muscular changes in achalasia might be just reactive changes.

Effect of proton pump inhibition on the gastric volume: assessed by magnetic resonance imaging

BACKGROUND

Proton pump inhibitor (PPI) therapy is known to suppress gastric acid secretion. Thus PPI therapy may decrease gastric volume and gastric contents available for gastro-oesophageal reflux by decreasing acid secretion.

AIM

To determine the effect of PPI therapy on the gastric volume after a standard meal.

METHODS

A total of nine healthy subjects were studied using magnetic resonance imaging, before and after a standard liquid meal mixed with a paramagnetic contrast to help demarcate the gastric region. Images were acquired for a total of 90 min after the meal. Studies were conducted before and following esomeprazole twice daily for 7 days. Images were analysed to determine the gastric liquid volume.

RESULTS

Gastric volume, 15 min after the meal peaked to 611 +/- 37 mL on the control day and 539 +/- 30 mL following the PPI administration (P < 0.001). Average gastric volume remained significantly lower (56 +/- 9 mL, P < 0.05) on the PPI therapy from 5 to 75 min after the meal.

CONCLUSIONS

Proton pump inhibitor therapy causes a significant reduction in the gastric contents volume during first 75 min after the meal. In addition to increasing the gastric pH, PPI therapy may decrease the frequency of gastro-oesophageal reflux by decreasing the volume of gastric contents.

Liquid in the gastroesophageal segment promotes reflux, but compliance does not: a mathematical modeling study

The mechanical force relationships that distinguish normal from chronic reflux at sphincter opening are poorly understood and difficult to measure in vivo. Our aim was to apply physics-based computer simulations to determine mechanical pathogenesis of gastroesophageal reflux. A mathematical model of the gastroesophageal segment (GES) was developed, incorporating the primary anatomical and physiomechanical elements that drive GES opening and reflux. In vivo data were used to quantify muscle stiffness, sphincter tone, and gastric pressure. The liquid lining the mucosa was modeled as an "effective liquid film" between the mucosa and a manometric catheter. Newton's second law was solved mathematically, and the space-time details of opening and reflux were predicted for systematic variations in gastric pressure increase, film thickness, muscle stiffness, and tone. "Reflux" was defined as "2 ml of refluxate entering the esophagus within 1 s." GES opening and reflux were different events. Both were sensitive to changes in gastric pressure and sphincter tone. Reflux initiation was extremely sensitive to the liquid film thickness; the protective function of the sphincter was destroyed with only 0.4 mm of liquid in the GES. Compliance had no effect on reflux initiation, but affected reflux volume. The presence of abnormal levels of liquid within the collapsed GES can greatly increase the probability for reflux, suggesting a mechanical mechanism that may differentiate normal reflux from gastroesophageal reflux disease. Compliance does not affect the probability for reflux, but affects reflux volume once it occurs. Opening without reflux suggests the existence of "gastroesophageal pooling" in the distal esophagus, with clinical implications.