Pao, Y. C.

Abstract A modified myocardium-blood composite model enables the temporal changes in instantaneous extension and contraction of in vivo myocardial fiber to be computed by using the measured blood volume fractions and wall thicknesses in the investigated left ventricular region. A 16 time-increment study of 6 dogs shows that myocardial fiber may undergo an average length change of 62% and −38% during the diastolic and systolic phases of cardiac cycle, respectively. Two comparable results had been obtained previously, but the new method is much simpler, removes the incompressibility assumption and takes into consideration the intravascular blood in the ventricular wall.

Abstract For biomechanics analysis of body organs, finite element method [1∼3] is the practical tool for dealing with the complex geometric shapes and material composition involved. Either for direct computation of the stresses and strains in the body organ or inverse determination of its material properties, the change of geometrical shapes and dimensions and the change of the loadings, both in time, must be accurately recorded. Moreover, fast imaging techniques [4] and a vast volume of computer storage memory are necessary for acquisition of such temporal data, particularly if finite-element biomedical algorithms are to be developed for routine use. This paper reports a chronological development of finite-element inverse determination of global and regional material properties, passive diastolic stiffness and active systolic contractile strength of the in vivo heart wall. A collection of computer algorithms has been accumulated as a result of continuing collaborative research on cardiopulmonary dynamics by the authors and their co-workers since 1973.

Abstract For occlusion experiments of 9 dogs [1], the infarcted and not-infarcted regions of left ventricular cross sections have been investigated by application of a plane-strain finite-element method to determine the change in the wall passive stiffness, or, Young’s modulus E [2]. The present paper reports how the instantaneous strain equation derived from the myocardium-blood composite model [3,4] can be utilized to obtain a formula for calculation of the ratio of extended myocardial fiber length in the infarcted (IN) region and that in the not-infarcted (NI) region of left ventricular cross section during the diastole phase of cardiac cycle. This formula uses the blood volume fraction (f) data [5] listed in Table 1 and the ventricular wall thickness (t) directly measurable from the LV walls as visualized in short-axis tomographic images of the LV.

Abstract The true cross-sectional shape and dimensions of a coronary arterial wall with an atherosclerotic plaque obtained at postmortem, Fig. 1, is utilized for dilation rupture study related to the balloon angioplasty process. Plane-strain, finite-element analysis [1,2] of the shape changes and stress distributions of the cross section are performed by an incremental loading approach. The location of rupture is predicted by a dilation study ranging from 10 kPa to 120 kPa (about 1.2-fold of atmospheric pressure).

Abstract Formulas have been derived for computation of the cross sectional area, location of the centroid, and moments of inertia making direct use of the binary-data which are to be collected from computer-tomographical scanning of porous materials. Bone data are applied to demonstrate the developed computational procedure and interactive operation of QuickBASIC programs.

The constitutive equation with stress-dependent coefficients for laminated composite is derived and employed for iterative determination of myocardial fiber’s stiffness equation Ef = Kσf + C from myocardial strip’s stiffness equation Es = Ksσs + Cs. The strip’s stiffness constants Ks and Cs are estimated by the least-square curve fitting of the stress-strain data experimentally obtained from uniaxially stretching of strips of left ventricular heart wall excised from seven canine hearts. The values of K and C computed at selected fiber orientations across the thickness of the strip and using three, five, and ten-layer approximations are reported.