Development of a finite element based three-dimensional simulation of esophageal motility with the potential to explain the physiological effects of weightlessness

Introduction/Aims. A finite element (FE) based simulation of the human esophagus and a kinematic simulation of esophageal pathophysiological motility were developed. The FE simulation is applicable to the determination of physiological and biomechanical conditions of a normal human esophageal swallow. The kinematic simulation allows visualization of normal peristalsis and a gastro-esophageal reflux disease (GERD) type peristalsis. Methods. The ROSS (Center for Bioinformatics, NASA AMES) suite of programs were used to develop a high-resolution, anatomically accurate, and mesh based 3-D reconstruction of the human esophagus. This reconstruction was based on the National Library of Medicine's Visible Male serial section dataset. Custom code (C++) that was developed to be used in conjunction with the ROSS visualization program was employed to produce the kinematic simulations. The Mesh Generation Module of MARC/Mentat (MSC software, Ca.) was used to produce the 3-D hexahedral element model from the ROSS surface reconstruction. The simulations were solved on an SGI Octane SI R10000 using the nonlinear finite element analysis (FEA) software MARC7.3. Material properties and boundary conditions were determined from experiments on patients and tissue samples as reported in the literature. Results. The kinematic simulation produces an interactive visualization of peristalsis in a 3-D computer model of the esophagus. The peristaltic wave is viewable from any angle and from the inside or outside of the esophagus. In the GERD esophagus simulation the lower esophageal sphincter (LES) remains relaxed post peristalsis. In GERD patients, a relaxed LES often allows for reflux of gastric contents into the esophagus. The FE simulation results indicate that FEA is a valid numerical modeling tool for esophageal motor function. The FE simulation predicted the shape and time of transport for a bolus propulsed through the esophagus and is corroborated through comparison with multi-dimensional VFG imaging. Conclusions. The anatomically accurate 3-dimensional simulation model of the human esophagus allows visualization of changes in esophageal bolus geometry and the differences in the forces needed to transport the bolus to the stomach. The results of the FE simulation suggest that the nonlinear finite element method has potential usefulness as a simulation tool for esophageal physiological function under a variety of environments and conditions, including weightlessness. The FE model may provide useful information in the study of pathophysiological esophageal biomechanics. The two simulations provide a unique perspective into the function of the esophagus.