Hysteresis of the lower esophageal sphincter: relevance to the pathogenesis of esophageal achalasia and its phenotypes.

Hysteresis is a change in strain for a given repeated stress; it is a material property of the viscoelastic tissues. We aimed to determine hysteresis of the esophagogastric junction (EGJ) in patients with esophageal achalasia and differences in EGJ hysteresis in different achalasia phenotypes. In a cross-sectional study design, we measured the change in EGJ distensibility index (DI) with repeated distensions (a marker of hysteresis) and the effects of atropine on the DI using functional lumen imaging probe in 40 patients with esophageal achalasia (types 1, 2, and 3). The DI increased significantly with second distension (hysteresis) as compared with first distension, but not with subsequent ones. Atropine, which ablates active smooth muscle contraction, had no effect on the DI value. Patients with type 1 esophageal achalasia and those with severe dilatation (stage III and IV disease) had a higher DI and lower hysteresis, as compared with esophageal achalasia subtypes 2 and 3. A low DI following atropine suggests that the passive elements (viscoelastic properties) of EGJ are an important cause of low DI in esophageal achalasia. Hysteresis of the EGJ, a material property of the viscoelastic tissue, is different in different achalasia subtypes.NEW & NOTEWORTHY Hysteresis, a key biomechanical property of the esophagogastric junction (EGJ), may play a crucial role in achalasia pathogenesis. Using functional lumen imaging probe (FLIP) topography, we demonstrate that EGJ distensibility increases with repeated distensions, with subtype-dependent variability. Our findings suggest that hysteresis is associated with achalasia progression and treatment outcomes, offering novel insights into esophageal biomechanics. These results may guide refinements in FLIP-based diagnostics and inform future therapeutic approaches targeting determinants of hysteresis.