Role of functional endoscopy

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.