  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. Irregular weakening or stiffening of the EGJ
muscles result in changes to its opening and closing patterns which can
progress into esophageal disorders. 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. Using clinical FLIP data, we plotted the pressure-area hysteresis
at the EGJ location and distinguished two major loop types, a pressure dominant
loop (PDL) and a tone dominant loop (TDL). In this study, we aimed to identify
the key characteristics that define each loop type and find what causes the
inversion from one loop to another. To do so, the clinical observations were
reproduced using 1D simulations of flow inside a FLIP device located in the
esophagus, and the work done by the EGJ wall over time was calculated. This
work was decomposed into active and passive components, which revealed the
competing mechanisms that dictate the loop type. These mechanisms are esophagus
stiffness, fluid viscosity, and the EGJ relaxation pattern. In PDL, the leading
source of energy in the cycle is coming from the fluid pressure increase from
the peristaltic contraction wave, and in TDL the leading source of energy in
the cycle is coming from the contraction and relaxation of the EGJ tone.
