School of Biomedical Engineering, Colorado State University, Fort Collins, CO, 80523, USA.
Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, 80523, USA.
Acta Biomater. 2022 Oct 15;152:290-299. doi: 10.1016/j.actbio.2022.08.043. Epub 2022 Aug 24.
The increasing evidence of stress-strain hysteresis in large animal or human myocardium calls for extensive characterizations of the passive viscoelastic behavior of the myocardium. Several recent studies have investigated and modeled the viscoelasticity of the left ventricle while the right ventricle (RV) viscoelasticity remains poorly understood. Our goal was to characterize the biaxial viscoelastic behavior of RV free wall (RVFW) using two modeling approaches. We applied both quasi-linear viscoelastic (QLV) and nonlinear viscoelastic (NLV) theories to experimental stress relaxation data from healthy adult ovine. A three-term Prony series relaxation function combined with an Ogden strain energy density function was used in the QLV modeling, while a power-law formulation was adopted in the NLV approach. The ovine RVFW exhibited an anisotropic and strain-dependent viscoelastic behavior relative to anatomical coordinates, and the NLV model showed a higher capacity in predicting strain-dependent stress relaxation than the QLV model. From the QLV fitting, the relaxation term associated with the largest time constant played the dominant role in the overall relaxation behavior at most strains from early to late diastole, whereas the term associated with the smallest time constant was pronounced only at low strains at early diastole. From the NLV fitting, the parameters showed a nonlinear dependence on the strain. Overall, our study characterized the anisotropic, nonlinear viscoelasticity to capture the elastic and viscous resistances of the RVFW during diastole. These findings deepen our understanding of RV myocardium dynamic mechanical properties. STATEMENT OF SIGNIFICANCE: Although significant progress has been made to understand the passive elastic behavior of the right ventricle free wall (RVFW), its viscoelastic behavior remains poorly understood. In this study, we originally applied both quasi-linear viscoelastic (QLV) and nonlinear viscoelastic (NLV) models to published experimental data from healthy ovine RVFW. Our results revealed an anisotropic and strain-dependent viscoelastic behavior of the RVFW. The parameters from the NLV fitting showed nonlinear relationships with the strain, and the NLV model showed a higher capacity in predicting strain-dependent stress relaxation than the QLV model. These findings characterize the anisotropic, nonlinear viscoelasticity of RVFW to fully capture the total (elastic and viscous) resistance that is critical to diastolic function.
越来越多的证据表明，大型动物或人体心肌存在应力-应变滞后现象，这就需要对心肌的被动黏弹性行为进行广泛的描述。最近有几项研究调查并建立了左心室的黏弹性模型，而右心室（RV）的黏弹性仍然知之甚少。我们的目标是使用两种建模方法来描述 RV 游离壁（RVFW）的双轴黏弹性行为。我们将拟线性黏弹性（QLV）和非线性黏弹性（NLV）理论应用于健康成年绵羊的实验应力松弛数据。在 QLV 建模中，采用了三参数 Prony 松弛函数和 Ogden 应变能密度函数，而在 NLV 方法中采用了幂律公式。与解剖坐标相比，绵羊 RVFW 表现出各向异性和应变依赖性的黏弹性行为，NLV 模型在预测应变依赖性的应力松弛方面比 QLV 模型表现出更高的能力。从 QLV 拟合来看，在早期至晚期舒张的大多数应变下，与最大时间常数相关的松弛项在整体松弛行为中起着主导作用，而与最小时间常数相关的松弛项仅在早期舒张的低应变下明显。从 NLV 拟合来看，参数表现出对应变的非线性依赖性。总的来说，我们的研究描述了各向异性、非线性黏弹性，以捕捉舒张期间 RVFW 的弹性和粘性阻力。这些发现加深了我们对 RV 心肌动态力学特性的理解。
尽管在理解右心室游离壁（RVFW）的被动弹性行为方面已经取得了重大进展，但它的黏弹性行为仍未得到很好的理解。在这项研究中，我们最初将拟线性黏弹性（QLV）和非线性黏弹性（NLV）模型应用于健康绵羊 RVFW 的已发表实验数据。我们的结果揭示了 RVFW 的各向异性和应变依赖性黏弹性行为。NLV 拟合的参数与应变呈非线性关系，NLV 模型在预测应变依赖性的应力松弛方面比 QLV 模型表现出更高的能力。这些发现描述了 RVFW 的各向异性、非线性黏弹性，以充分捕捉对舒张功能至关重要的总（弹性和粘性）阻力。
