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Studies of Esophageal Transport and ...

Kou, Wenjun.

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Studies of Esophageal Transport and Emptying Based on Fully-resolved Computational Models.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Studies of Esophageal Transport and Emptying Based on Fully-resolved Computational Models./
Author:	Kou, Wenjun.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2016,
Description:	245 p.
Notes:	Source: Dissertation Abstracts International, Volume: 78-02(E), Section: B.
Contained By:	Dissertation Abstracts International78-02B(E).
Subject:	Biomechanics. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10160480
ISBN:	9781369153873

Studies of Esophageal Transport and Emptying Based on Fully-resolved Computational Models.
Kou, Wenjun.

Studies of Esophageal Transport and Emptying Based on Fully-resolved Computational Models. - Ann Arbor : ProQuest Dissertations & Theses, 2016 - 245 p.

Source: Dissertation Abstracts International, Volume: 78-02(E), Section: B.

Thesis (Ph.D.)--Northwestern University, 2016.

The first part of this thesis presents studies on esophageal transport based on fully-resolved simulation models. Esophageal transport is a bio-physical process that transfers an ingested food bolus from the pharynx to the stomach through the esophageal tube. This process is also referred to as esophageal peristalsis clinically. This process involves complicated interactions among the esophageal wall, neurally controlled muscle activation and the food bolus. Due to the complexity, however, there is no previous fully-coupled model in the literature that is able to resolve the underlying interactions. Therefore, this part of work consists of developing fully-resolved computational models on esophageal transport, and conducting case studies on issues of clinical interests. Specifically, two fully-resolved computational models are developed and validated during the completion of this thesis. The first esophageal transport model is developed using the fiber-based immersed boundary method, referred to here as the IB-fiber esophageal transport model. The IB-fiber esophageal transport model describes each esophageal layer as a three-dimensional fiber network that consists of springs and beams. To consider more realistic and complicated behaviors of biological tissues, we later develop our second fully-resolved model on esophageal transport using the immersed-boundary-finite-element (IB-FE) method. We refer to this model as the IB-FE esophageal transport model, which considers each esophageal layer as a fiber-reinforced material.

ISBN: 9781369153873Subjects--Topical Terms:

548685
Biomechanics.

Studies of Esophageal Transport and Emptying Based on Fully-resolved Computational Models.
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100 1 $a Kou, Wenjun. $0 (orcid)0000-0003-2582-2070 $3 3342862
245 1 0 $a Studies of Esophageal Transport and Emptying Based on Fully-resolved Computational Models.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2016
300 $a 245 p.
500 $a Source: Dissertation Abstracts International, Volume: 78-02(E), Section: B.
500 $a Adviser: Neelesh A. Patankar.
502 $a Thesis (Ph.D.)--Northwestern University, 2016.
520 $a The first part of this thesis presents studies on esophageal transport based on fully-resolved simulation models. Esophageal transport is a bio-physical process that transfers an ingested food bolus from the pharynx to the stomach through the esophageal tube. This process is also referred to as esophageal peristalsis clinically. This process involves complicated interactions among the esophageal wall, neurally controlled muscle activation and the food bolus. Due to the complexity, however, there is no previous fully-coupled model in the literature that is able to resolve the underlying interactions. Therefore, this part of work consists of developing fully-resolved computational models on esophageal transport, and conducting case studies on issues of clinical interests. Specifically, two fully-resolved computational models are developed and validated during the completion of this thesis. The first esophageal transport model is developed using the fiber-based immersed boundary method, referred to here as the IB-fiber esophageal transport model. The IB-fiber esophageal transport model describes each esophageal layer as a three-dimensional fiber network that consists of springs and beams. To consider more realistic and complicated behaviors of biological tissues, we later develop our second fully-resolved model on esophageal transport using the immersed-boundary-finite-element (IB-FE) method. We refer to this model as the IB-FE esophageal transport model, which considers each esophageal layer as a fiber-reinforced material.
520 $a Based on developed fully-resolved computational models on esophageal transport, we conduct several application studies on issues that are of clinical interests. First, we study the role of each type of muscle activation, i.e. circular muscle (CM) contraction and longitudinal muscle (LM) shortening, and their coordination in esophageal transport. We find that CM contraction generates a high squeezing pressure and plays a primary role in esophageal transport. LM shortening increases muscle CSA, which helps to strengthen CM contraction. Advancing LM shortening decreases esophageal distensibility in the bolus region. Lagging LM shortening no longer helps esophageal transport. Those results on dis-coordination may shed light on the correlation between motor dysfunctions and motility disorders. We then study the role of esophageal mucosa in esophageal transport. We find that a compliant mucosa helps accommodate the incoming bolus and lubricate the moving bolus. Bolus transport is marginally achieved without mucosa or with mucosa replaced by muscle. A stiff mucosa greatly impairs bolus transport due to lowered esophageal distensibility and increased luminal pressure. This implies that mucosal stiffening may be relevant in diseases characterized by reduced esophageal distensibility, elevated intra-bolus pressure, and/or hypertensive muscle contraction such as eosinophilic esophagitis (EoE) and jackhammer esophagus. We also study the role of muscle fiber architecture and multiple contraction waves in esophageal transport. We find that different fiber architecture features different characteristics during esophageal transport. Helical fiber architecture features lower circumferential wall stress, higher esophageal distensibility and more pronounced axial shortening. Non-uniform fiber architecture features a distinctive luminal pressure trough between two high luminal pressure strips, similar to the peristaltic transition zone (also referred to as pressure transition zone in the literature). This may suggest that peristaltic transition zone could have a possible myogenic origin that is due to non-uniform muscle fiber architecture. The studies on muscle activation and esophageal mucosa are based on the IB-fiber esophageal transport model. The studies on muscle fiber architecture and the peristaltic transition zone are based on the IB-FE esophageal transport model.
520 $a The second part of this thesis is about esophageal emptying. Esophageal emptying is a process, where the bolus is emptied to the stomach from the esophageal tube. This process follows esophageal transport (i.e. esophageal peristalsis) and involves interactions among the esophageal wall, the gastric wall, neurally controlled muscle activation, and the bolus. To resolve those interactions, we develop a fully-coupled bolus-esophageal-gastric model. In particular, we introduce a simple model to include the passive and active functions of the lower esophageal sphincter (LES). We conduct three groups of case studies. The first group is about the influence of a non-relaxed LES. The second group is about the influence from the tissue anisotropy. The third group is about the influence of LES stiffness and gastric wall stiffness. From the first group, we find that a non-relaxed LES features a sustained high wall stress along the LES segment and obstruction of bolus emptying. For cases with tissue anisotropy in the second group, we find that a weaker part (i.e. a more compliant part) suffers from a higher deformation as well as higher wall shear stress. More importantly, the weaker part seems to take a higher pressure load when the bolus is filled in and emptied from the LES segment. This implies a degradation cycle in which a weaker tissue becomes much weaker due to an increased load, a likely pathway leading to clinically observed esophageal lower diverticulum. From the third group of studies, we find that a right bulge tends to develop during esophageal emptying if the LES becomes compliant. The bulge is simply due to asymmetric configuration of the gastric wall with respect to the esophageal tube. This might explain why a right bulge near the esophageal lower end is more frequently seen than a left bulge in clinics. Moreover, we find the bulge is more pronounced with a higher stiffness of the gastric wall and lower stiffness of the LES. This implies that the competition between the LES stiffness and gastric wall stiffness might be another implication related to the esophageal lower diverticulum. The simulation also suggests that one remedy to alleviate the right bulge is to increase the right-part LES stiffness. An excessive increase of the right-part LES stiffness, however, could otherwise lead to a left bulge.
590 $a School code: 0163.
650 4 $a Biomechanics. $3 548685
650 4 $a Biomedical engineering. $3 535387
650 4 $a Mechanical engineering. $3 649730
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690 $a 0548
710 2 $a Northwestern University. $b Theoretical and Applied Mechanics. $3 1025697
773 0 $t Dissertation Abstracts International $g 78-02B(E).
790 $a 0163
791 $a Ph.D.
792 $a 2016
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10160480