ABSTRACT
Objective To establish a numerical model of human mitral valve and simulate its closing process, so as to analyze stress distributions on the valve apparatuses, study the interaction between leaflets of mitral valve and chordae tendineae, and explore the relationship between the force of chordae tendineae and their thickness. Methods A geometric model of human mitral valve was constructed. On the basis of the geometric model, the finite element model was established by defining the element type, material attributes, contacts, loads and constraints. Parameters such as stress, velocity and displacement were calculated after solving the model. Results The stress distribution on the valve was non-uniform. The clefts between the scallops in the posterior leaflet were always under the highest load. When no chordae tendineae were attached, the leaflets turned over to the side of the atrium. When chordea tendineae were attached, the anterior and posterior leaflet could close up successfully. Different chordae tendineae applied different forces to the valve. The strut chorea tendineae attached to the anterior leaflet applied highest force among all the chordea tendineae. The correlation coefficient between the thickness of chordae tendineae and their force was 0.954. Conclusions The two zones with higher stresses, namely the center of the leaflet and the clefts between the three scallops in the posterior leaflet, are also the positions of mitral valve cleft in clinic. Chordea tendineae can apply the pulling force on the leaflets while the mitral valve is under load, thus the leaflets won’t turn over to the side of atrium and the valve can close up in time. Chordea tendineae with thicker anatomic structure always apply a higher force on the leaflets.
ABSTRACT
AIM: Accommodation is one of the most important functions of human eye, while its mechanism is still under discussion. This paper aimed to study accommodation mechanism with numerical simulation.METHODS: A simulation model was constructed to study the mechanism of accommodation based on the experimental data derived from published resources. The displacement and pressure are applied on the model to study the deformation of lens during accommodating.RESULTS: The simulation showed that, as the eye was accommodating, the thickness of the lens increased linearly,and the lens diameter decreased linearly. The optical power of the lens increased as the accommodation increased. This result was accord with the public facts in accommodation.Furthermore, the pressure was found to have a great influence on the shape of the lens and the optical power. The lens became thinner and flatter as the pressure increased and the pressure caused a remarkable increase of lens' optical power.CONCLUSION: The outcome of this paper is consistent with the Helmholtz's hypothesis on accommodation to some extent. The analytical model presented in this paper can be used in the theoretical study of the accommodation mechanism of the human lens.