Comparison of biaxial mechanical properties of excised endocardium and epicardium.

A complete understanding of cardiac mechanics requires knowledge of the mechanical properties of each of the tissues that comprise the heart, Data and constitutive relations are available for the nonlinear multiaxial behavior of epicardium and noncontracting myocardium, but there have been no comparable results for endocardium. In this paper, we present biaxial mechanical data for endocardium and epicardium excised from the same bovine hearts. The data reveal that these two membranes behave differently; endocardium exhibits a greater stiffness in the low-strain range. Moreover, quantification of endocardial behavior requires a seven-parameter, polynomial-exponential pseudostrain-energy function w, whereas epicardium can be described by a four-parameter exponential w. Comparison of our current findings with previous results on canine epicardium reveals further that canine and bovine epicardium behave similarly, although the latter is more extensible. Thus there appear to be marked species differences.