title: Mechanics of the mitral valve: a critical review, an in vivo parameter identification, and the effect of prestrain.
abstract: Alterations in mitral valve mechanics are classical indicators of valvular heart disease, such as mitral valve prolapse, mitral regurgitation, and mitral stenosis. Computational modeling is a powerful technique to quantify these alterations, to explore mitral valve physiology and pathology, and to classify the impact of novel treatment strategies. The selection of the appropriate constitutive model and the choice of its material parameters are paramount to the success of these models. However, the in vivo parameters values for these models are unknown. Here, we identify the in vivo material parameters for three common hyperelastic models for mitral valve tissue, an isotropic one and two anisotropic ones, using an inverse finite element approach. We demonstrate that the two anisotropic models provide an excellent fit to the in vivo data, with local displacement errors in the sub-millimeter range. In a complementary sensitivity analysis, we show that the identified parameter values are highly sensitive to prestrain, with some parameters varying up to four orders of magnitude. For the coupled anisotropic model, the stiffness varied from 119,021 kPa at 0 % prestrain via 36 kPa at 30 % prestrain to 9 kPa at 60 % prestrain. These results may, at least in part, explain the discrepancy between previously reported ex vivo and in vivo measurements of mitral leaflet stiffness. We believe that our study provides valuable guidelines for modeling mitral valve mechanics, selecting appropriate constitutive models, and choosing physiologically meaningful parameter values. Future studies will be necessary to experimentally and computationally investigate prestrain, to verify its existence, to quantify its magnitude, and to clarify its role in mitral valve mechanics.
authors.affiliation: Department of Mechanical Engineering, Stanford University, 496 Lomita Mall, Stanford, CA, 94305, USA, mkrausch@stanford.edu.
authors.forename: Manuel K
authors.initials: MK
authors.lastname: Rausch
authors.forename: Nele
authors.initials: N
authors.lastname: Famaey
authors.forename: Tyler O'Brien
authors.initials: TO
authors.lastname: Shultz
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bothe
authors.forename: D Craig
authors.initials: DC
authors.lastname: Miller
authors.forename: Ellen
authors.initials: E
authors.lastname: Kuhl
mesh_terms: D000818:Animals; D016880:Anisotropy; D001696:Biomechanical Phenomena; D024022:Fibrillar Collagens / Q000737:chemistry; D020342:Finite Element Analysis; D006352:Heart Ventricles / Q000503:physiopathology; D007430:Intraoperative Care; D008297:Male; D008943:Mitral Valve / Q000503:physiopathology* / Q000601:surgery; D008955:Models, Cardiovascular; D012756:Sheep; D013314:Stress, Mechanical
chemical_list: D024022:Fibrillar Collagens