Dynamic and static tensile mechanical properties of myocardial tissue

摘要

Introduction: Heart disease is a significant cause of morbidity and mortality that affects 1.3 million Canadians annually. Coronary artery disease (CAD) is a leading cause of heart disease and is due to progressive accumulation of arterial plaque resulting in occlusion of the arterial lumen and abnormal myocardial contractility. Computed Tomography Coronary Angiography (CTCA) is used to exclude significant CAD in patients with low-intermediate pre-test probability. However, dynamic anthropomorphic CT phantom devices that realistically mimic normal and diseased cardiac tissues are required to test new imaging techniques and algorithms that target ultralow radiation dose and under varying hemodynamic conditions. Materials and Methods: The elasticity of myocardial tissue was tested under static and dynamic conditions. Tensile testing was performed to obtain the Young's modulus and a dynamic mechanical analyzer (DMA) induced a frequency sweep to determine the complex (dynamic) modulus. A frequency range of 0.5Hz to 3.5Hz was analyzed as these frequencies correspond to human heart rates of 30 to 210bpm. Multiple tissue samples were taken from each pig and lamb heart, these animal models were chosen as they are close human analogues and are commonly used as replacements for human tissue.The heart tissue was tested while freshly sacrificed without any intervening freeze-thaw cycles to ensure the integrity of the muscle tissue. The tissue was placed in a balanced salt solution and tested at 37°C to simulate in vitro conditions. Results and Discussion: Preliminary data (mean ± SD): The tensile and complex moduli were tested on 6 pig and lamb hearts; tensile modulus of lamb = 0.06 ±0.03 (n=15 samples) and for pig =0.04 ± 0.03 (n=11 samples); the complex modulus for lamb = 0.03Mpa at 0.5Hz to 0.06 Mpa at 3.5Hz ± 0.02 (n=15 samples) and for pig = 0.03Mpa at 0.5Hz to 0.06 Mpa at 3.5Hz ± .01 (n=15 samples) and both exhibited a linear trend. These values indicate that myocardial tissue behaves similarly to soft rubbers and stiffens under higher frequency loads. Moreover, for tensile testing there was no statistical difference between individual hearts or animals (P values of 0.235,0.483, and 0.73 between the animals, pig hearts, and lamb hearts respectively). Conclusions: The static and dynamic moduli of myocardial tissue in pig and lamb hearts is between 0.02 and 0.1Mpa which is similar to soft, rubber-like materials. This quantitative data will inform selection and fabrication of customized biomaterials for construction of the myocardium in a dynamic anthropomorphic tissue realistic heart phantom.