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This paper presents a formulation to identify muscle activities from the variation in shapes of organs during swallowing. We assume that each organ consists of a three-dimensional hyperelastic body, and the contraction movement of the muscle is caused by a contractive inelastic stress in the organ. A function distributed in the organ domain to control the magnitude of the inelastic stress is chosen as a design variable in the same manner as the density in the topology optimization problem of density variation type. The identification problem is formulated as a problem of determining the design variable that minimizes an objective cost function defined by the squared L 2 norm of the reaction force in the normal direction on the boundary when an enforced displacement to fit the varied boundary of the organ and the inelastic stress modeling the muscle activity are applied. The finite deformation problem of the hyperelastic body is analyzed using the finite element method. The direction of the muscle fiber is assumed to be the direction of the minimum principal stress obtained as the solution to the finite deformation problem. The solution to the identification problem is presented based on a scheme using the H 1 gradient method for the topology optimization problem of density variation type. A numerical example using a previously developed model of the tongue is introduced to demonstrate the effectiveness of the proposed approach.

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This study investigated the influence of the rheological and tribological parameters of a food bolus on the organ surface during swallowing. A swallowing simulator was developed based on a three-dimensional moving-particle simulation with a realistic human organ model. The simulator enables numerical comparisons using a standard human model based on food models with different rheological and tribological parameters. Through a parametric study, we can successfully characterize several aspiration patterns for low viscosity with high-density and high-viscosity food models. Our results revealed that the main cause of the before aspiration was the fast bolus arrival at the epiglottis and not the small particles. The results also revealed that to control the outbreak of the spray for aspiration restraints, it is important to control the lubrication of the bolus. This study is not a simple aspiration simulation. Moreover, it can contribute to building an evaluation system that connects the properties of a food bolus with the aspiration phenomenon without any medical radiation risks. Based on the results, we conclude that our swallowing simulator is a useful tool for estimating and evaluating the aspiration phenomena, including the relationship between human organ movement and rheological and tribological properties of the food and organ surface.