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In developed nations, swallowing disorders and aspiration pneumonia have become serious problems. We developed a method to simulate the behavior of the organs involved in swallowing to clarify the mechanisms of swallowing and aspiration. The shape model is based on anatomically realistic geometry, and the motion model utilizes forced displacements based on realistic dynamic images to reflect the mechanisms of human swallowing. The soft tissue organs are modeled as nonlinear elastic material using the Hamiltonian MPS method. This method allows for stable simulation of the complex swallowing movement. A penalty method using metaballs is employed to simulate contact between organ walls and smooth sliding along the walls. We performed four numerical simulations under different analysis conditions to represent four cases of swallowing, including a healthy volunteer and a patient with a swallowing disorder. The simulation results were compared to examine the epiglottic downfolding mechanism, which strongly influences the risk of aspiration.

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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.