Ultrasonic determination of the anisotropy of Young's modulus of fixed tendon and fixed myocardium.

The linear elastic properties of a soft tissue exhibiting a unidirectional arrangement of reinforcing fibers may be described in terms of the five independent elastic stiffness coefficients C11, C13, C33, C44, and C66. In previous studies, ultrasonic measurements of these coefficients for formalin fixed specimens of bovine Achilles tendon and normal human myocardium were reported. In the present study these results are used to analyze the anisotropy of Young's modulus of these tissues. For formalin fixed tendon a value of 1.37 GPa is obtained for Young's modulus along the fiber axis of the tissue, and a value of 0.0706 GPa is obtained perpendicular to the fibers. For formalin fixed myocardium, values of 0.101 and 0.0311 GPa parallel and perpendicular to the fibers, respectively, are obtained. Based on the results for the angular dependence of Young's modulus from unidirectional specimens of myocardium, a model is introduced to estimate these features for the more complicated fiber architecture of the left ventricular wall.