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Review Role of functional endoscopy
Ippei Tanaka1,2orcid, Haruhiro Inoue1orcid

DOI: https://doi.org/10.5946/ce.2026.111
Published online: July 30, 2026

1Digestive Disease Center, Showa Medical University Koto Toyosu Hospital, Tokyo, Japan

2Department of Medicine, University of British Columbia, Vancouver, BC, Canada

Correspondence: Ippei Tanaka Digestive Disease Center, Showa Medical University Koto Toyosu Hospital, 5-1-38 Toyosu, Koto-ku, Tokyo 135-8577, Japan E-mail: ippeitanaka777@gmail.com
• Received: March 14, 2026   • Revised: May 7, 2026   • Accepted: May 19, 2026

© 2026 Korean Society of Gastrointestinal Endoscopy

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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  • Endoscopy has evolved to include the assessment of gastrointestinal function, an approach known as functional endoscopy. In this review, we summarize the current evidence on the endoscopic pressure-integrated system (EPSIS) as a representative modality in this field. Initial studies demonstrated the diagnostic utility of the EPSIS for gastroesophageal reflux disease by revealing significant associations between EPSIS parameters and 24-hour pH monitoring, as well as endoscopic findings such as erosive esophagitis and Barrett’s esophagus. The usefulness of the EPSIS was also demonstrated in diagnosing achalasia and in the evaluation of treatment efficacy following antireflux mucosal interventions and peroral endoscopic myotomy. Dynamic changes in the gastric cardia during EPSIS were observed as the intragastric pressure increased. These changes were categorized into three sequential phases, referred to as the phase concept. In healthy individuals, all three phases function appropriately, whereas in patients with acid reflux, dysfunction is observed in one or more phases. Despite these promising findings, several aspects of the EPSIS remain to be clarified, and most previous studies have been conducted at a single center. Future multicenter prospective studies are warranted to accumulate robust evidence and further establish the clinical utility of the EPSIS.
  • Keywords: Cardia; Endoscopy; Esophagitis; Gastroesophageal reflux
Gastroesophageal reflux disease (GERD) is a common chronic upper gastrointestinal disorder with an increasing prevalence worldwide.1,2 According to the Lyon Consensus criteria, GERD is diagnosed when patients present with typical symptoms such as heartburn or regurgitation in conjunction with endoscopically confirmed mucosal erosion at the esophagogastric junction.3 However, approximately 50%–80% of patients with GERD symptoms do not exhibit erosive changes on endoscopy and are classified as having non-erosive reflux disease (NERD).4
The gold standard for diagnosing NERD is 24-hour impedance and pH monitoring; however, this approach has inherent drawbacks as the procedure is prolonged, requiring 24 hours for completion, and the insertion of a nasal catheter into the esophagus can cause substantial patient discomfort. The use of an indwelling capsule-based Bravo pH monitoring system represents a potential alternative; however, concerns regarding its diagnostic accuracy and high cost persist.5 As a result, there is an increasing demand for a simple yet accurate diagnostic modality for NERD. In an attempt to address this, we developed an endoscopic pressure study integrated system (EPSIS) as a novel endoscopic assessment tool to dynamically evaluate lower esophageal sphincter (LES) function (Fig. 1).6
The EPSIS has been increasingly recognized as an effective and helpful diagnostic tool for GERD, particularly in Japan. In this review, we summarize the latest insights into the EPSIS as a representative modality for functional endoscopy and discuss future perspectives in this field.
The EPSIS is used to measure intragastric pressure (IGP) during routine gastrointestinal endoscopy. During its initial development, a pressure-measuring catheter was inserted through the endoscope to assess the IGP. More recently, the procedure has been simplified such that the pressure-sensing tube can be directly connected to the endoscope channel, improving its ease of use.7
During CO₂ insufflation, both the basal IGP and maximum IGP can be measured. Analysis of the IGP waveform allows for classification into flat or uphill patterns. However, to prevent adverse events, such as Mallory-Weiss syndrome, it is essential to maintain an IGP below 25 mmHg. We retrospectively reviewed 1,205 EPSIS procedures to evaluate the incidence of EPSIS-related adverse events. Petechial hemorrhage in the stomach was observed in 32 patients (2.7%), and Mallory-Weiss syndrome occurred in three patients (0.25%). No patients required endoscopic hemostasis.8 Therefore, all EPSIS-related complications were considered minor, and the EPSIS procedure was considered safe.
The EPSIS procedure is typically performed under CO₂ insufflation and sedation to minimize patient discomfort during the procedure and is conventionally conducted using a standard-diameter endoscope. However, we have demonstrated that EPSIS procedures can be successfully performed using a thin endoscope.9 In light of this finding, the necessity of routine sedation, which is currently considered standard practice for the EPSIS procedure, warrants reconsideration.
The relationship between the EPSIS and pH monitoring has been investigated previously.6 In this earlier study, 56 patients who underwent both examinations were evaluated, and an optimal cutoff value of 18.7 mmHg for the diagnosis of NERD was identified. Using this threshold, the EPSIS demonstrated a sensitivity of 74.2% (95% confidence interval [CI], 56.8%–86.3%) and a specificity of 57.1% (95% CI, 39.1%–73.5%) for the detection of GERD.
In addition, the flat IGP waveform pattern showed high diagnostic performance for NERD, with a sensitivity of 71.0% (95% CI, 53.4%–83.9%) and a specificity of 82.1% (95% CI, 64.4%–92.1%). When these two diagnostic factors were combined, EPSIS parameters—namely, a maximum IGP ≤18.7 mmHg and a flat waveform pattern—were highly reliable predictors of both GERD (odds ratio [OR], 16.05; 95% CI, 3.23–79.7) and NERD (OR, 14.7; 95% CI, 2.37–90.8).
However, the classification of a waveform as uphill or flat is inherently subjective, which is a limitation of this approach. To address this issue, an additional study was conducted to assess the diagnostic utility of the pressure gradient, which is defined as the pressure increase divided by the insufflation time. This parameter demonstrated high diagnostic accuracy, with an area under the receiver operating characteristic curve of 0.81.10
Furthermore, the wave height, calculated as the pressure difference between the peak and adjacent nadir of the IGP waveform, has also been reported to be useful for identifying abnormal acid exposure times, with a proposed cutoff value of 3.1 mmHg.11 The wave height likely reflects respiration-related IGP fluctuations caused by diaphragmatic motion and stomach–LES interaction, with inspiratory diaphragmatic descent transiently increasing IGP. These pressure variations may be exaggerated in conditions such as a sliding hiatal hernia, providing a plausible physiological basis for their association with abnormal esophageal acid exposure. Nevertheless, further studies are required to validate these hypotheses.
Collectively, these findings indicate that the EPSIS has high diagnostic accuracy for both NERD and GERD, as defined by pH monitoring. In the future, the EPSIS may be used as a screening modality in conjunction with routine gastrointestinal endoscopy in patients presenting with GERD symptoms.
The association between EPSIS parameters and gastroesophageal reflux–related endoscopic findings, including erosive esophagitis (EE) and Barrett’s esophagus (BE), was evaluated in a separate study that included 104 patients.12 Patients with EE or BE showed significantly lower IGP-max values compared with those without these conditions (EE, 16.0 vs. 18.8 mmHg; BE, 15.7 vs. 19.6 mmHg; p<0.001). Additionally, a flat EPSIS waveform pattern was observed more frequently in patients with EE and BE than in those without these conditions (82.8% vs. 37.3% and 69.0% vs. 37.1%, respectively; p<0.001).
These findings indicate that EPSIS parameters are significantly associated with the endoscopic findings of GERD, such as EE and BE. Future studies with larger sample sizes are warranted to investigate the differences in EPSIS parameters between short-segment BE and long-segment BE, as well as to clarify changes in EPSIS parameters according to GERD severity.
When the EPSIS procedure was performed in patients with achalasia diagnosed using high-resolution manometry, gastroscopy, and esophagography, a markedly steeper and sharper uphill waveform pattern was observed compared with the normal uphill pattern.13 This finding reflects the underlying pathophysiology of increased LES pressure.
Interestingly, after peroral endoscopic myotomy (POEM) in patients with achalasia, mean EPSIS parameters, including the maximum IGP (IGP-max), IGP difference, and IGP gradient, decreased significantly (IGP-max, 15.0 vs. 19.8 mmHg; IGP difference, 8.0 vs. 12.2 mmHg; both p<0.001; IGP gradient, 0.26 vs. 0.43 mmHg/s, p<0.001). Furthermore, the mean postoperative waveform gradient was significantly lower in the patients who developed GERD after POEM than in those without GERD.
Collectively, these findings indicate that the EPSIS demonstrates high diagnostic performance not only for GERD but also for achalasia.
The initial management of GERD and NERD typically involves acid-suppressive therapy. However, despite adequate treatment, approximately 30%–40% of patients continue to experience reflux symptoms, a condition referred to as proton pump inhibitor (PPI)- or potassium-competitive acid blocker (P-CAB)-refractory GERD.14,15
For such patients, we performed antireflux mucosal interventions (ARMI), including antireflux mucosectomy, antireflux mucosal ablation, and antireflux mucosal plasty.16-21 The fundamental concept of these procedures is to narrow the gastric cardia and reduce gastroesophageal reflux by ablating or resecting the surrounding mucosa of the cardia, thereby enhancing the antireflux barrier. The efficacy of these endoscopic treatments has been supported by systematic reviews and meta-analyses.22-24
When the EPSIS procedure was performed after ARMI, postoperative IGP-max increased significantly from 15.2 to 18.0 mmHg (p=0.004), and the pressure gradient improved from 0.16 to 0.28 mmHg/s (p<0.001).25 These findings suggest that the EPSIS may serve as a useful adjunctive assessment tool, although 24-hour pH monitoring remains the standard method for post-procedural evaluation following ARMI.
During the EPSIS procedure, we observed dynamic changes in the gastric cardia using a retroflexed endoscopic view. These changes were categorized into three sequential phases, referred to as the phase concept26: phase 1 (gastric phase), phase 2 (esophageal phase), and phase 3 (recovery phase).
In phase 1, characterized by a low IGP, the gastroesophageal flap valve was clearly visualized. As the IGP increased to a moderate level, the flap valve became elongated and flattened. During this phase, LES contraction is reflexively enhanced to maintain the antireflux barrier despite increased pressure. Therefore, this phase is referred to as phase 2. In phase 3, with further elevation of the IGP, LES relaxation occurs, allowing gastric gas to escape into the esophagus and subsequently through the mouth, accompanied by esophageal peristalsis. This coordinated sequence represents a functional antireflux barrier. Accordingly, the development of GERD may be attributed to the dysfunction or failure of one or more phases of this mechanism.
The phase concept provides a useful framework for understanding antireflux physiology. However, further studies are required to validate its applicability in gastroesophageal junction disorders and clarify its association with other diagnostic modalities.
Although the EPSIS is a representative modality of functional endoscopy, a previous study did not use the EPSIS to estimate IGP.27 The findings of this study revealed that the gastric folds on the forward endoscopic view gradually flattened as the IGP increased. When the folds were completely flattened, the mean IGP measured using the EPSIS at the corresponding time point was 17.7 mmHg.
Given that the optimal cutoff value for GERD has been reported to be 18.7 mmHg, as described above, the likelihood of GERD may be low when the gastric folds are completely flattened. However, as this study included a limited number of cases, further validation with a larger cohort is warranted.
The EPSIS is useful not only for the diagnosis of GERD but also for the evaluation of achalasia and the assessment of treatment efficacy following ARMI and POEM. Because the EPSIS can be performed during routine gastrointestinal endoscopy, it has the potential to be applied in a wide range of clinical settings.
Fig. 1.
Endoscopic pressure study integrated system (EPSIS). The EPSIS was developed as a novel endoscopic assessment tool to dynamically evaluate lower esophageal sphincter function. By attaching the EPSIS tube (yellow arrow) to the endoscope channel, the intragastric pressure (IGP, pink arrow) can be measured during routine gastrointestinal endoscopy. The image below shows the display during the EPSIS procedure. The vertical and horizontal axes represent pressure and time, respectively.
ce-2026-111f1.jpg
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      Fig. 1. Endoscopic pressure study integrated system (EPSIS). The EPSIS was developed as a novel endoscopic assessment tool to dynamically evaluate lower esophageal sphincter function. By attaching the EPSIS tube (yellow arrow) to the endoscope channel, the intragastric pressure (IGP, pink arrow) can be measured during routine gastrointestinal endoscopy. The image below shows the display during the EPSIS procedure. The vertical and horizontal axes represent pressure and time, respectively.

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      Role of functional endoscopy
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