Yukihiro Michiwaki

Numerical simulation of interaction between organs and food bolus during swallowing and aspiration

The mechanism of swallowing is still not fully understood, because the process of swallowing is a rapid and complex interaction among several involved organs and the food bolus. In this work, with the aim of studying swallowing and aspiration processes noninvasively and systematically, a computer simulation method for analyzing the involved organs and water (considered as the food bolus) is proposed. The shape and motion of the organs involved in swallowing are modeled in the same way as in our previous study, by using the Hamiltonian moving particle simulation (MPS) method and forced displacements on the basis of motion in a healthy volunteer. The bolus flow is simulated using the explicit MPS method for fluid analysis. The interaction between the organs and the bolus is analyzed using a fluid-structure coupling scheme. To validate the proposed method, the behavior of the simulated bolus flow is compared qualitatively and quantitatively with corresponding medical images. In addition to the healthy motion model, disorder motion models are constructed for reproducing the aspiration phenomenon by computer simulation. The behaviors of the organs and the bolus considered as the food bolus in the healthy and disorder motion models are compared for evaluating the mechanism of aspiration.

Development of a numerical simulator of human swallowing using a particle method (Part 2. Evaluation of the accuracy of a swallowing simulation using the 3D MPS method)

The aim of this study was to develop and evaluate the accuracy of a three-dimensional (3D) numerical simulator of the swallowing action using the 3D moving particle simulation (MPS) method, which can simulate splashes and rapid changes in the free surfaces of food materials. The 3D numerical simulator of the swallowing action using the MPS method was developed based on accurate organ models, which contains forced transformation by elapsed time. The validity of the simulation results were evaluated qualitatively based on comparisons with videofluorography (VF) images. To evaluate the validity of the simulation results quantitatively, the normalized brightness around the vallecula was used as the evaluation parameter. The positions and configurations of the food bolus during each time step were compared in the simulated and VF images. The simulation results corresponded to the VF images during each time step in the visual evaluations, which suggested that the simulation was qualitatively correct. The normalized brightness of the simulated and VF images corresponded exactly at all time steps. This showed that the simulation results, which contained information on changes in the organs and the food bolus, were numerically correct. Based on these results, the accuracy of this simulator was high and it could be used to study the mechanism of disorders that cause dysphasia. This simulator also calculated the shear rate at a specific point and the timing with Newtonian and non-Newtonian fluids. We think that the information provided by this simulator could be useful for development of food products, medicines, and in rehabilitation facilities.

Modelling of swallowing organs and its validation using Swallow Vision®, a numerical swallowing simulator

Abstract Swallowing process occurring within the mouth and throat regions is so quick and complex that the three-dimensional (3D) motion of each organ involved in the process has not yet been visualised even by the state-of-the-art medical imaging technology. To overcome this issue, a realistic organ model has been developed based on the actual medical images and validated using swallowing simulation (by Swallow Vision ® ). A three-dimensional organ model coupled with a bolus flow model has been developed using a mesh-free moving particle simulation (MPS) method. Two organ models have been developed based on the computed tomography (CT) and video-fluorography (VF) images of a healthy male volunteer and a male patient with mild dysphagia, and validated by simulation. The results showed that these two models well-visualised each organ and the bolus flow, which were consistent with the actual images. The realistic organ model is deemed to be useful for acquiring a deeper understanding of the biomechanics of swallowing. Further work, especially on the segmentation and registration of medical images, will enable to develop various organ models from medical images, which may help in performing swallowing simulations in the clinical practice.

Numerical visualisation of physical values during human swallowing using a three-dimensional swallowing simulator ‘Swallow Vision®’ based on the moving particle simulation method: Part 1: quantification of velocity, shear rate and viscosity during swallowing

ABSTRACT The aim of this study is to visualise changes in physical values of food bolus during swallowing to correlate the movement of human organs and bolus flow configuration using Swallow Vision®, a three-dimensional human swallowing simulator. Swallow Vision was developed using realistic human organ models, food bolus models, and the meshless three-dimensional moving particle simulation (MPS) method. The human organ model used to create Swallow Vision was reconstructed using computed tomography and video-fluorography images of a healthy volunteer. The extracted physical values, such as velocity, shear rate and viscosity were correlated with the movement of human organs and bolus flow configuration. The velocity and the shear rate were in good agreement with other researchers’ results, and the simulation results are hence considered adequate. Swallow Vision will be helpful for understanding swallowing biomechanics, as well as for identifying appropriate foods for people with swallowing difficulties or dysphagia.

PA 08-1-1080 Clarification of the mechanisms and visualization of choking on toys using the computer simulator swallow vision®

Choking on toys is a common global occurrence. However, since there are no methods to observe the process of airway obstruction during human and animal experiments, clarification of the mechanisms has not been elucidated. To solve this problem, we visualized and analyzed choking on toys using Swallow Vision®, a computer simulator of swallowing behavior. The model of the oral cavity to esophagus was constructed based on CT images of a 9-month-old boy and videofluorography images of a 9-month-old girl. The simulated toy shapes included a sphere, hemisphere, rectangle, disk, and cylinder. The parameters of the toys, such as friction coefficients were measured during the experiments. To simulate the behaviors of organs and toys, the Hamiltonian MPS method, which is a particle method for analyzing the fluid–structure interaction, was applied. Particle methods do not require the generation of a mesh. From the simulation results of 48 toy models of various sizes, shapes, and parameters, it was found that the risks of choking were high when the toys were spherical and 6 to 20 mm in size. Toys less than 6 mm were accidentally swallowed. Depending on the occlusion position, choking could be classified as either laryngeal or pharyngeal obstruction. Regarding the mechanism of the toy’s entry into the pharynx, a toy larger than 10 mm must be transferred to the pharynx by a sudden induction of the swallowing reflex, because the fauces, which is the boundary between the oral cavity and the pharynx, is narrow. On the other hand, in the case of a small toy, aspiration might also be the cause; however, the influence of air flow must be studied in the future.

Development of Musculoskeletal Model to Estimate Muscle Activities During Swallowing

Swallowing, or deglutition, is well known as a process to transport bolus of food from mouth to stomach, whereas it is difficult to understand its physiological mechanism because it involves in complex neuromuscular coordination. In order to understand swallowing mechanism in terms of muscle activity, we develop a musculoskeletal model in which muscles around the hyoid bone and the thyroid cartilage are represented as wire actuators. The changes of muscle lengths are calculated to estimate muscle activities during normal swallowing as a static analysis using the musculoskeletal model. The results of this study would contribute to provide greater insight into swallowing and to improve treatments for dysphagia.

Development of musculoskeletal model for the hyoid bone during swallowing

Swallowing, or deglutition, is simple and smooth process to transport food and drink from the mouth to the stomach, whereas it is difficult to understand its physiological mechanism because it consists of complex neuromuscular coordination. Movements of the hyoid are important to describe swallowing in pharyngeal phase. We therefore develop a musculoskeletal model of the hyoid based on anatomical knowledge to verify activities of muscles around the hyoid in swallowing. Individual muscle force is estimated by the inverse dynamics computation and optimization. The estimation results of muscle force are compared to the results found in a previous study. The results of this study contributes to provide greater insight into swallowing and to improve treatments for dysphagia.