Biaxial mechanical properties of human pericardium and canine comparisons

The two-dimensional mechanical properties of human pericardium from seven males undergoing coronary artery bypass surgery were studied. A 25-mm square piece of parietal pericardium overlying the right ventricle was excised. An approximately 8-mm square target was marked at the center, and its dimension was measured electrooptically. When immersed in physiological saline at 37 degrees C, the specimen was subjected to biaxial isotropic loading. Large deformations developed in the beginning of the loading; the pericardium became increasingly stiffer when load was increased, and then became almost inextensible. As in canine pericardium [Lee et al., Am. J. Physiol. 249 (Heart Circ. Physiol. 18): H222-H230, 1985], hysteresis was present and tension-stretch relationship was insensitive to loading frequency during cyclic loading, relaxation of tension was substantial, and creep was insignificant. Unlike canine specimens, however, human pericardium was nearly isotropic and almost three times as thick [mean 0.55 +/- 0.02 mm (SD)]. The human tension-area relation for isotropic loading could be described by an exponential function and was found to shift significantly to the left of the canine. Therefore, human pericardium is less extensible than canine.