Computational study of lung lobar sliding and the mechanics of breathing
Creators: name: Galloy, Adam
Publisher: name: University of Iowa
Year: 2024
Subjects: Helmholtz-Hodge decomposition
lobar sliding
lung
tissue mechanics
Biomechanics
Finite Element Analysis
Mechanics

description: Improved knowledge of lung mechanics can aid in the development of new lung disease treatment and diagnosis strategies. One poorly understood aspect of lung mechanics is the sliding of the lung lobes against each other along the lobar fissures. Large variance between different subjects’ fissure anatomy such as incomplete, missing, or auxiliary lobar fissures could affect lobar sliding and, as a result, their lung mechanics. Previous researchers have hypothesized that lung lobar sliding reduces parenchymal distortion in the lungs, but this hypothesis remains untested. In general, our understanding of lobar sliding – including its visualization and characterization – remains poor. This knowledge gap limits our ability to formulate specific, testable hypotheses about lobar sliding and its effects on lung mechanics. In addition, medical technologies such as motion-adaptive radiation therapy, dynamic medical image reconstruction, and lung image registration may benefit from an improved understanding of sliding kinematics.
description: To address these knowledge gaps, the first aim for this project was to develop a subject-specific contact mechanics model of the lungs suitable for simulating lobar sliding and its impact on lung deformations. The model geometry and thoracic cavity motion boundary conditions were derived from CT scans of the lungs. Lung parenchyma was modeled as a compressible isotropic finite elastic material. Sliding contact constraints were applied between each pair of lobes and between each lobe and the thoracic cavity whose prescribed displacement drove parenchymal deformation and lobar sliding. Contact parameters were optimized to increase stability, accuracy, and computation speed of the model.
description: The second aim of this project was to test the hypothesis that lung lobar sliding reduces parenchymal distortion using the contact mechanics model. For each subject in our cohort, lung deformation was simulated with and without lobar sliding and the resulting parenchymal distortion quantified for both scenarios. Consistent with the hypothesis, the mean parenchymal distortion was significantly lower in the models allowing lobar sliding than the ones that did not allow lobar sliding. This effect was more pronounced in the right lung which has three lobes than the left lung which has two. These results suggest that patients with missing or incomplete lobar fissures will experience more parenchymal distortion which may result in more difficulty breathing.
description: The third aim of the project was to quantitatively analyze lobar sliding kinematics based on the contact mechanics simulations. A mathematically rigorous formulation for quantifying sliding distance and visualizing sliding motion was applied for the first time to lung lobar sliding. Using Helmholtz-Hodge decomposition the sliding displacement vector fields from simulations were decomposed into three components describing the relative stretching, rotation, and translation between lobes using Helmholtz-Hodge decomposition. This preliminary analysis found that translation, not rotation, was the predominant component in lobar sliding displacement fields; however, the boundary conditions required to produce a unique decomposition may be inflating the translational component.