Abstract
BackgroundThe biomechanical simulation of the human respiratory system is expected to be a useful tool for the diagnosis and treatment of respiratory diseases. Because the deformation of the thorax significantly influences airflow in the lungs, we focused on simulating the thorax deformation by introducing contraction of the intercostal muscles and diaphragm, which are the main muscles responsible for the thorax deformation during breathing.MethodsWe constructed a finite element model of the thorax, including the rib cage, intercostal muscles, and diaphragm. To reproduce the muscle contractions, we introduced the Hill-type transversely isotropic hyperelastic continuum skeletal muscle model, which allows the intercostal muscles and diaphragm to contract along the direction of the fibres with clinically measurable muscle activation and active force–length relationship. The anatomical fibre orientations of the intercostal muscles and diaphragm were introduced.ResultsThorax deformation consists of movements of the ribs and diaphragm. By activating muscles, we were able to reproduce the pump-handle and bucket-handle motions for the ribs and the clinically observed motion for the diaphragm. In order to confirm the effectiveness of this approach, we simulated the thorax deformation during normal quiet breathing and compared the results with four-dimensional computed tomography (4D-CT) images for verification.ConclusionsThorax deformation can be simulated by modelling the respiratory muscles according to continuum mechanics and by introducing muscle contractions. The reproduction of representative motions of the ribs and diaphragm and the comparison of the thorax deformations during normal quiet breathing with 4D-CT images demonstrated the effectiveness of the proposed approach. This work may provide a platform for establishing a computational mechanics model of the human respiratory system.
Highlights
The biomechanical simulation of the human respiratory system is expected to be a useful tool for the diagnosis and treatment of respiratory diseases
Because segmenting the intercostal muscles and diaphragm from the computed tomography (CT) slices was difficult, 3D models of the intercostal muscles and diaphragm were constructed in the following way: the positions of intercostal muscles and diaphragm attached to the bones were first determined by referencing an anatomy textbook [13]; the surfaces of intercostal muscles were created by connecting the muscle attachments between upper and lower rib bones; regarding that diaphragm is the boundary of the chest cavity, the surface of the diaphragm was generated as to attach the lung bottom
Based on the formulation given in the section entitled ‘Transversely isotropic hyperelastic material model of respiratory muscle’, the incompressible transversely isotropic hyperelastic material model was implemented in a nonlinear finite element analysis program developed in-house, which was validated in the authors’ previous works
Summary
The biomechanical simulation of the human respiratory system is expected to be a useful tool for the diagnosis and treatment of respiratory diseases. The human respiratory system has a complex structure that stretches from the trachea to the alveoli and involves many physiological phenomena such as the airflow, lung deformation, oxygen exchange, pleural pressure distribution, alveolar pressure distribution, respiratory muscle activation, and chest movement. Chronic obstructive pulmonary disease (COPD) is characterized by the presence of airflow limitation, which is assessed by spirometry test or medical images such as multi detector-row computed tomography (MDCT) [1] in the diagnosis processes. Because breathing and all subsequent physiological phenomena are closely related to the thorax deformation produced by respiratory muscle contraction, our current goal was to establish a computational mechanics model to simulate the contractions of the diaphragm and intercostal muscles, which are the main muscles responsible for thorax deformation [5]
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