  Esophageal transport is a physiological process that mechanically transports
an ingested food bolus from the pharynx to the stomach via the esophagus, a
multi-layered muscular tube. This process involves interactions between the
bolus, the esophagus, and the neurally coordinated activation of the esophageal
muscles. In this work, we use an immersed boundary (IB) approach to simulate
peristaltic transport in the esophagus. The bolus is treated as a viscous fluid
that is actively transported by the muscular esophagus, which is modeled as an
actively contracting, fiber-reinforced tube. A simplified version of our model
is verified by comparison to an analytic solution to the tube dilation problem.
Three different complex models of the multi-layered esophagus, which differ in
their activation patterns and the layouts of the mucosal layers, are then
extensively tested. To our knowledge, these simulations are the first of their
kind to incorporate the bolus, the multi-layered esophagus tube, and muscle
activation into an integrated model. Consistent with experimental observations,
our simulations capture the pressure peak generated by the muscle activation
pulse that travels along the bolus tail. These fully resolved simulations
provide new insights into roles of the mucosal layers during bolus transport.
In addition, the information on pressure and the kinematics of the esophageal
wall due to the coordination of muscle activation is provided, which may help
relate clinical data from manometry and ultrasound images to the underlying
esophageal motor function.
