Normal gastroesophageal motilty is important to live a comfortable and healthy life. Motility disorders result in impaired transport of ingested food which can lead to extreme discomfort and severe damage to the walls of the esophagus. Significant work has been done to study gastroesophageal motility using advanced diagnostic tools such as High-Resolution Manometry (HRM) and Endolumenal Functional Lumen Imaging Probe (EndoFLIP). This thesis delves deeper into the biomechanics of esophageal contractility and motility by building mathematical models for FLIP and the upper gastrointestinal tract. Clinical data collected using FLIP catheters is then augmented with the help of these numerical models to reveal the mechanical work done during normal and abnormal contractility in the esophagus. Work done by repetitive antegrade contractions is computed for healthy subjects and several disease groups to understand the differences in energy spent during peristaltic pumping in these devices. In addition to peristaltic work, planimetry and pressure data are used to compute the work done to open the esophagogastric junction (EGJ) which is the barrier between the esophagus and stomach. This complex sphincter mechanism is responsible for preventing the acidic stomach contents from entering the esophageal lumen. In patients with impaired EGJ opening, the work required to open the EGJ was computed which revealed important differences between patients with impaired relaxation vs. those with impaired opening due to inadequate pressure. Thus, these mechanical work metrics can be used as physiomarkers to improve diagnosis and phenotyping of various disease states that affect esophageal motility and timely opening of the EGJ. The second part of this thesis summarizes the development of detailed, fully three-dimensional models of the upper gastrointestinal tract that account for the interaction between the fluid contents with the solid walls and also the differences in densities between various fluids present in the GI tract. The fiber architecture of the stomach walls is quite complex as the gastric walls have a nontrivial geometric structure. This work presents a strategy to assign fiber directions for the longitudinal and circular muscle layers of the stomach walls. By systematically activating these fibers, gastric peristalsis is simulated and flow patterns inside the stomach are visualized. In addition to this, gravity-driven bolus transport is presented by constructing a pill-shaped bolus consisting of a heavier fluid. Finally, a model problem to study acid reflux is presented by simulating buoyancy-driven retrograde flow from the stomach. Although simulated density ratios were lower than those observed in subjects, the successful implementation of a closed sphincter opening to allow retrograde flow offers a foundation on which future models can be based to study acid reflux and the effects of an impaired lower esophageal sphincter.

Creator

• Acharya, Shashank

DOI

• https://doi.org/10.21985/n2-psxd-v625

Subject

• Computational physics
• Fluid mechanics
• Biomechanics

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:15539
• etdadmin_upload_816410

Keyword

• gastrointestinal biomechanics
• reduced-order modeling
• esophageal motility disorders
• peristalsis
• fluid-structure interaction
• immersed boundary method

Date created

• 2021-01-01

Resource type

• Dissertation

Rights statement

• In Copyright