RECONSTRUCTION OF LOADS IN THE FIBROSA AND VENTRICULARIS OF PORCINE AORTIC VALVES

The main structural components of aortic valve cusps, the fibrosa and ventricularis, are pre loaded by virtue of their attachment to each ot her. The fibrosa is under compression and the ventricularis is under t ension. Once separated from each other, these internal stresses are re lieved, and the fibrosa elongates and the ventricularis shrinks. It th en becomes impossible to determine what fraction of the load is carrie d by the two layers at a given strain, using the standard superpositio n of tension vs strain curves. To enable the superposition approach, w e needed to adjust the tension/strain curves of the fibrosa and ventri cularis, and duplicate the pre load that exists in these layers. We, t herefore, iteratively shifted these curves and compared their arithmet ic sum to the tension curve for the whole intact cusp, using a sum-of- squares error function. The best fits occurred when the fibrosa and ve ntricularis were shifted to the right and left by amounts correspondin g to a true strain of epsilon = 0.26 and 0.10 for the fibrosa and vent ricularis in the radial directions. In the circumferential direction, the best fit was achieved for shifts of epsilon = -0.11 and 0.010 for the fibrosa and ventricularis, respectively. This 26% compressive stra in of the radial fibrosa compares well with direct observations. The r econstructed tension curves indicate that the ventricularis carries mu ch of the radial loads, whereas circumferentially the two layers share loads equally up to 25% strain, beyond which the fibrosa takes over.