Computational Modeling of Healthy Myocardium in Diastole

Abstract

In order to better understand the mechanics of the heart and its disorders, engineers increasingly make use of the finite element method (FEM) to investigate healthy and diseased cardiac tissue. However, FEM is only as good as the underlying constitutive model, which remains a major challenge to the biomechanics community. In this study, a recently developed structurally based constitutive model was implemented to model healthy left ventricular myocardium during passive diastolic filling. This model takes into account the orthotropic response of the heart under loading. In-vivo strains were measured from magnetic resonance images (MRI) of porcine hearts, along with synchronous catheterization pressure data, and used for parameter identification of the passive constitutive model. Optimization was performed by minimizing the difference between MRI measured and FE predicted strains and cavity volumes. A similar approach was followed for the parameter identification of a widely used phenomenological constitutive law, which is based on a transversely isotropic material response. Results indicate that the parameter identification with the structurally based constitutive law is more sensitive to the assigned fiber architecture and the fit between the measured and predicted strains is improved with more realistic sheet angles. In addition, the structurally based model is capable of generating a more physiological End-Diastolic Pressure-Volume Relationship in the ventricle.

Effects of using the unloaded configuration in predicting the in vivo diastolic properties of the heart

“…The animals used in this work received care in compliance with the protocols approved by the Institutional Animal Care and Use Committee at the University of Pennsylvania in accordance with the guidelines for humane care (National Institutes of Health Publication 85-23, revised 1996). The data used in the current study is from the same animal cohort that was used in the study of Nikou et al [9], in which many of the experimental details can be found. Briefly, the endocardium and epicardium of the LV were contoured from the 3D SPAMM (SPAtial Modulation of Magnetization) MR images and fit with 3D surface geometry.…”

“…Briefly, the passive material parameters (C, b f , b t , b fs ) were optimized within the ranges previously reported for normal myocardium [12]. Diastolic strain was calculated from the 3D SPAMM MR images using a custom optical flow plug-in for ImageJ to derive 3D displacement flow fields [9]. The objective function that was minimized during the optimization was taken to be the mean squared error (MSE) between MRI measured and FE predicted strains as well as the normalized difference in LV cavity volume.…”

“…This provided two FE models for each of the five animals; (1) a model with a reference geometry based on early-diastolic filling and (2) a model with a reference geometry that is based on the numerically unloaded state. Next, passive material parameters of the myocardium were identified using a technique that utilizes a combination of MRI/pressure data, FE modeling, and numerical optimization [9]. The ultimate goal of this study was to estimate the in-vivo material properties of left ventricular myocardium, as well as quantify how the material properties and end-diastolic stress distributions were affected by the choice of reference configuration.…”

Transmural gradients of myocardial structure and mechanics: Implications for fiber stress and strain in pressure overload

“…the sheet structure) of the myocardium has surfaced more recently (Arts et al, 2001), (Ashikaga et al, 2005), (Ashikaga et al, 2008), (Chen et al, 2005), (Cheng et al, 2005), (Cheng et al, 2008), (Coppola and Omens, 2008), (Costa et al, 1999), (Covell, 2008), (Nikou et al, 2015), (Pope et al, 2008). Since it is commonly argued that sheet structures contribute to wall thickening by allowing large shear deformations to occur (Costa et al, 1999), (Cheng et al, 2005), the orientation, dispersion, and mechanical properties of these sheets are undoubtedly important factors contributing to fiber stress and strain.…”

Biaxial quantification of passive porcine myocardium elastic properties by region

“…However, most of these studies have focused on one region only, namely, the LV (Nikou et al, 2016, Wise et al, 2016. The stress-strain curve of the LV has then been used as being representative of the whole heart.…”