Pressure – area loop based phenotypic classification and mechanics of esophagogastric junction physiology *

The esophagogastric junction (EGJ) is located at the distal end of the esophagus, and acts as a valve allowing swallowed materials to enter the stomach and preventing acid reflux. Weakening of the EGJ muscles results in a more compliant valve, which changes its opening and closing patterns and can progress into esophageal diseases. Therefore, understanding the physics behind the opening and closing cycle of the EGJ provides a mechanistic insight into its function and can help identify the underlying conditions that cause its degradation. From clinical data, we plotted the pressure-area hysteresis at the EGJ location and identified two major loop types, one with opening curve above closing, and the other with closing curve above the opening. The following study aimed to identify the key characteristics that define each loop type and find what causes the inversion between one loop to another. To do so, the clinical observations were reproduced using simulations and the work done by the EGJ was calculated. This work was separated into active and passive parts which revealed the competing mechanisms that dictate the loop type. These parameters are esophagus stiffness, fluid viscosity, and the EGJ relaxation pattern.