Simulation studies of the role of esophageal mucosa in bolus transport

A Review of In Vitro and In Silico Swallowing Simulators: Design and Applications

Swallowing is a primary and complex behaviour that transports food and drink from the oral cavity, through the pharynx and oesophagus, into the stomach at an appropriate rate and speed. To understand this sophisticated behaviour, a tremendous amount of research has been carried out by utilising the in vivo approach, which is often challenging to perform, poses a risk to the subjects if interventions are undertaken and are seldom able to control for confounding factors. In contrast, in silico (computational) and in vitro (instrumental) methods offer an alternate insight into the process of the human swallowing system. However, the appropriateness of the design and application of these methods have not been formally evaluated. The purpose of this review is to investigate and evaluate the state of the art of in vitro and in silico swallowing simulators, focusing on the evaluation of their mechanical or computational designs in comparison to the corresponding swallowing mechanisms during various phases of swallowing (oral phase, pharyngeal phase and esophageal phase). Additionally, the potential of the simulators is also discussed in various areas of applications, including the study of swallowing impairments, swallowing medications, food process design and dysphagia management. We also address current limitations and recommendations for the future development of existing simulators.

Rheology, Texture and Swallowing Characteristics of a Texture-Modified Dysphagia Food Prepared Using Common Supplementary Materials

A dysphagia diet is a special eating plan. The development and design of dysphagia foods should consider both swallowing safety and food nutritional qualities. In this study, the effects of four food supplements, namely vitamins, minerals, salt and sugar, on swallowing characteristics, rheological and textural properties were investigated, and a sensory evaluation of dysphagia foods made with rice starch, perilla seed oil and whey isolate protein was carried out. The results showed that all the samples belonged to foods at level 4 (pureed) in The International Dysphagia Diet Standardization Initiative (IDDSI) framework, and exhibited shear thinning behavior, which is favorable for dysphagia patients. Rheological tests showed that the viscosity of a food bolus was increased with salt and sugar (SS), while it decreased with vitamins and minerals (VM) at shear rates of 50 s^-1. Both SS and VM strengthened the elastic gel system, and SS enhanced the storage modulus and loss modulus. VM increased the hardness, gumminess, chewiness and color richness, but left small residues on the spoon. SS provided better water-holding, chewiness and resilience by influencing the way molecules were connected, promoting swallowing safety. SS brought a better taste to the food bolus. Dysphagia foods with both VM and 0.5% SS had the best sensory evaluation score. This study may provide a theoretical foundation for the creation and design of new dysphagia nutritional food products.

A mechanics-based perspective on the pressure-cross-sectional area loop within the esophageal body

Introduction: Plotting the pressure-cross-sectional area (P-CSA) hysteresis loops within the esophagus during a contraction cycle can provide mechanistic insights into esophageal motor function. Pressure and cross-sectional area during secondary peristalsis can be obtained from the functional lumen imaging probe (FLIP). The pressure-cross-sectional area plots at a location within the esophageal body (but away from the sphincter) reveal a horizontal loop shape. The horizontal loop shape has phases that appear similar to those in cardiovascular analyses, whichinclude isometric and isotonic contractions followed by isometric and isotonic relaxations. The aim of this study is to explain the various phases of the pressurecross-sectional area hysteresis loops within the esophageal body. Materials and Methods: We simulate flow inside a FLIP device placed inside the esophagus lumen. We focus on three scenarios: long functional lumen imaging probe bag placed insidethe esophagus but not passing through the lower esophageal sphincter, long functional lumen imaging probe bag that crosses the lower esophageal sphincter, and a short functional lumen imaging probe bag placed in the esophagus body that does not pass through the lower esophageal sphincter. Results and Discussion: Horizontal P-CSA area loop pattern is robust and is reproduced in all three cases with only small differences. The results indicate that the horizontal loop pattern is primarily a product of mechanical conditions rather than any inherently different function of the muscle itself. Thus, the distinct phases of the loop can be explained solely based on mechanics.

RNA-sequencing reveals molecular and regional differences in the esophageal mucosa of achalasia patients

Achalasia is an esophageal motility disorder characterized by the functional loss of myenteric plexus ganglion cells in the distal esophagus and lower esophageal sphincter. Histological changes have been reported in the esophageal mucosa of achalasia, suggesting its involvement in disease pathogenesis. Despite recent advances in diagnosis, our understanding of achalasia pathogenesis at the molecular level is very limited and gene expression profiling has not been performed. We performed bulk RNA-sequencing on esophageal mucosa from 14 achalasia and 8 healthy subjects. 65 differentially expressed genes (DEGs) were found in the distal esophageal mucosa of achalasia subjects and 120 DEGs were identified in proximal esophagus. Gene expression analysis identified genes common or exclusive to proximal and distal esophagus, highlighting regional differences in the disease. Enrichment of signaling pathways related to cytokine response and viral defense were observed. Increased infiltration of CD45+ intraepithelial leukocytes were seen in the mucosa of 38 achalasia patients compared to 12 controls. Novel insights into the molecular changes occurring in achalasia were generated in this transcriptomic study. Some gene changes observed in the mucosa of achalasia may be associated with esophagitis. Differences in DEGs between distal and proximal esophagus highlight the importance of better understanding regional differences in achalasia.

Myotomy technique and esophageal contractility impact blown-out myotomy formation in achalasia: an in silico investigation

We used in silico models to investigate the impact of the dimensions of myotomy, contraction pattern, the tone of the esophagogastric junction (EGJ), and musculature at the myotomy site on esophageal wall stresses potentially leading to the formation of a blown-out myotomy (BOM). We performed three sets of simulations with an in silico esophagus model, wherein the myotomy-influenced region was modeled as an elliptical section devoid of muscle fibers. These sets investigated the effects of the dimensions of myotomy, differing esophageal contraction types, and differing esophagogastric junction (EGJ) tone and wall stiffness at the myotomy affected region on esophageal wall stresses potentially leading to BOM. Longer myotomy was found to be accompanied by a higher bolus volume accumulated at the myotomy site. With respect to esophageal contractions, deformation at the myotomy site was greatest with propagated peristalsis, followed by combined peristalsis and spasm, and pan-esophageal pressurization. Stronger EGJ tone with respect to the wall stiffness at the myotomy site was found to aid in increasing deformation at the myotomy site. In addition, we found that an esophagus with a shorter myotomy performed better at emptying the bolus than that with a longer myotomy. Shorter myotomies decrease the chance of BOM formation. Propagated peristalsis with EGJ outflow obstruction has the highest chance of BOM formation. We also found that abnormal residual EGJ tone may be a co-factor in the development of BOM, whereas remnant muscle fibers at myotomy site reduce the risk of BOM formation.NEW & NOTEWORTHY Blown-out myotomy (BOM) is a complication observed after myotomy, which is performed to treat achalasia. In silico simulations were performed to identify the factors leading to BOM formation. We found that a short myotomy that is not transmural and has some structural architecture intact reduces the risk of BOM formation. In addition, we found that high esophagogastric junction tone due to fundoplication is found to increase the risk of BOM formation.

RoSE: A Robotic Soft Esophagus for Endoprosthetic Stent Testing

Soft robotic systems are well suited for developing devices for biomedical applications. A bio-mimicking robotic soft esophagus (RoSE) is developed as an in vitro testing device of endoprosthetic stents for dysphagia management. Endoprosthetic stent placement is an immediate and cost-effective therapy for dysphagia caused by malignant esophageal strictures from esophageal cancer. However, later stage complications, such as stent migration, could weaken the swallow efficacy in the esophagus. The stent radial force (RF) on the esophageal wall is pivotal in avoiding stent migration. Due to limited randomized controlled trials in patients, the stent design and stenting guidelines are still unconstructive. To address the knowledge deficit, we have investigated the capabilities of the RoSE by implanting two stents (stent A and B) of different radial stiffness characteristics, to measure the stent RF and its effect on the stent migration. Also, endoscopic manometry on the RoSE under peristalsis has been performed to study the impact of stenting and stent dysfunctionality on the intrabolus pressure signatures (IBPSs) in the RoSE, and further its effects on the swallowing efficacy. Each implanted stent in the RoSE underwent a set of experiments with various test variables (peristalsis velocity and wavelength, and bolus concentrations). In this study, the conducted tests are representative of the application of RoSE to perform a wide-ranging assessment of the stent behavior. The usability of RoSE has been discussed by comparing the results of stent A and B, for various combinations of the test variables mentioned earlier. The results have demonstrated that the stiffer stent B has a higher RF, whereas stent A maintained its RF at a low profile due to its lesser stiffness. The results have also implicated that a high RF is necessary to minimize the stent migration under prolonged peristaltic contractions in the RoSE. For the manometry experiments, stent A slightly increased the IBPS, but the stiffer stent B significantly decreased the IBPS, especially for the higher concentration boluses. It was found that if a stiffer stent buckles, it can reduce the swallow efficacy and cause recurrent dysphagia. Therefore, RoSE is an innovative soft robotic platform that is capable of testing various endoprosthetic stents, thereby offering a solution to many existing clinical challenges in the area of stent testing.

Immersed Methods for Fluid-Structure Interaction

Fluid-structure interaction is ubiquitous in nature and occurs at all biological scales. Immersed methods provide mathematical and computational frameworks for modeling fluid-structure systems. These methods, which typically use an Eulerian description of the fluid and a Lagrangian description of the structure, can treat thin immersed boundaries and volumetric bodies, and they can model structures that are flexible or rigid or that move with prescribed deformational kinematics. Immersed formulations do not require body-fitted discretizations and thereby avoid the frequent grid regeneration that can otherwise be required for models involving large deformations and displacements. This article reviews immersed methods for both elastic structures and structures with prescribed kinematics. It considers formulations using integral operators to connect the Eulerian and Lagrangian frames and methods that directly apply jump conditions along fluid-structure interfaces. Benchmark problems demonstrate the effectiveness of these methods, and selected applications at Reynolds numbers up to approximately 20,000 highlight their impact in biological and biomedical modeling and simulation.

Intrabolus Pressure Has Better Correlation Than Eosinophilia with Dysphagia Severity in Fibrostenotic Eosinophilic Esophagitis: A Pilot Study

Eosinophilic esophagitis is characterized by dysphagia with esophageal eosinophilia. We sought to determine if intrabolus pressure measurements on high-resolution manometry had any correlation with dysphagia improvement following standard therapy for patients with fibrostenotic eosinophilic esophagitis. Consecutive patients were prospectively enrolled at our swallowing center. Dysphagia scores, esophageal eosinophil counts, endoscopic reference scores, and intrabolus pressure measurements were compared at baseline and following therapy with 8 weeks of a proton-pump inhibitor and serial bougie dilation to a luminal diameter of 17 mm. Five patients were included in the study. The median age was 38 years. The average endoscopic reference score improved from 5.0 to 2.4 (p = 0.007). The mean esophageal diameter improved from 10.8 mm to 17.2 mm (p = 0.001). Dysphagia severity scores improved from a mean value of 34.2 to 10.8 (p = 0.004). Mucosal eosinophilia had no correlation with dysphagia severity. Mean intrabolus pressure improved from 21.8 mmHg to 11 mmHg (p = 0.001). There was strong correlation between a decrease in intrabolus pressure and improvement in dysphagia severity; however, this was not significant (p = 0.108). Intrabolus pressure has strong correlation with dysphagia severity following therapy for fibrostenotic eosinophilic esophagitis. Bougie dilation provides improvement in dysphagia despite persistent mucosal eosinophilia.