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Biomedical subjects

Y C Pao

Publications and source records attributed to Y C Pao.

17 recordsLinked to original sources
PubMed1998

Comparative characterization of the infarcted and reperfused ventricular wall muscles by finite element analysis and a myocardial muscle-blood composite model.

Two methods of characterizing the myocardial fiber bundles' property in the left ventricular wall are reviewed: (1) a myocardial muscle-blood composite model which assumes the myocardial muscle bundles to be incompressible but allows the intramural blood volume fraction to be taken into account, and (2) a two-dimensional finite element method for inverse determination of the myocardial Young's modulus during diastole by matching the computed and tomographically imaged cross-sectional areas near the mid-ventricular, short axis of the left ventricle at the end of diastole. The first method requires the measurements of ventricular wall thickness and the intramural blood volume fraction while the second method requires the image cross-sectional shapes and the corresponding left ventricular chamber pressures. This paper gives greater details of these two methods than in the previously presented progress reports and also presents a scheme for comparative characterization of the myocardial properties for an initial coronary artery occlusion and subsequent reperfusion study of the recently infarcted, left-ventricular wall regions. Furthermore, an attempt is made to correlate the data computed by the two methods. This may eventually lead to a reduction in the number of the required measurements needed for the two methods.

Animals↗
PubMed1993

A large-deformation, finite-element study of chondrodiatasis in the canine distal femoral epiphyseal plate.

A large-deformation, finite-element analysis was conducted to model stress fields around the developing growth plate as a first approach to comprehend the clinical application of traction for limb lengthening procedures. The model chosen was a cross section through the distal femoral growth plate of a 14-week-old dog. The chosen section passed through two of the conformational bends (mammillary processes) formed by the natural convolutions of the physis. Three different loading conditions were applied to the distal femoral epiphyseal model. The model also examined the effects of different values of Young's modulus of the growth-plate cartilage. The cortical bone in all cases, experienced the highest stresses. In the growth plate, the highest principal stresses occurred where the physis intersects cortical bone. There were localized stresses that were higher than those that caused fracture in a rabbit model [Guse et al., J. Orthop. Res. 7, 667-673 (1989)]. Results also indicated the following: a small tilt of 0.1 degree in loading application increases the maximum principal stresses and the von Mises stresses in certain regions of the growth plate by about 8%; the shearing stresses in the growth plate are sensitive to Young's modulus of the growth plate; and traction pins that do not grip the cancellous bone in the epiphysis will increase the regions of high principal stress in the growth plate.

Animals↗
PubMed1992

Bending and twisting of an in vivo coronary artery at a bifurcation.

Dynamic changes in the geometric shape and dimensions of a left coronary artery tree were extracted from the computer-tomographically reconstructed three-dimensional images of an in situ beating heart of an anesthetized dog. Wireframe models of the left coronary artery tree at 16 different instants of a cardiac cycle were constructed for the study of its flexing motion. For quantifying the local bending and twisting of the left coronary artery tree, the anatomic landmarks of the bifurcation points are selected as focussed locations. At these points, the space curves of the tree at different cardiac instants were first derived in parametric forms. Curvature and torsion expressions are next obtained in terms of the derivatives with respect to the parameter. This analysis revealed that during the initial contraction of the heart wall, a 2% reduction per millisecond in the radius of curvature occurred near the bifurcation point where the left circumflex coronary artery descends toward the apex of the heart. When the left ventricular chamber reached a maximum value, the radius of curvature was found to decrease at a rate of 2.3% ms-1. At the end of diastole, an increase in the radius of curvature at a rate of 5.7% ms-1 was observed. The twisting rates per unit length of artery near the bifurcation point of the selected artery were found to range from -0.62 to 0.63 degrees ms-1.

Animals↗
PubMed1990

Tooth surface fitting and three-dimensional display using hidden surface removal technique.

Bi-cubic parametric spline surface is applied for surface-fitting of the external surface and canal of tooth based on its crown-to-root, cross-sectional data obtained by X-ray scanning. For three-dimensional display of the fitted surfaces, a technique for fast removal of the hidden surfaces is also reported. The selection of the accumulated chord length or coordinate component as parameter make it possible to fit any kind of surface smoothly. For displaying or plotting a well-fitted surface, a method capable of discriminating the grades for sequential removal of the hidden surfaces is developed for substantial reduction of computing time.

Algorithms↗
PubMed1983

Dentin stresses in post-reconstructed teeth with diminishing bone support.

Dentin stresses from simulated functional loads to post-reinforced tooth models with four levels of periodontal support were calculated using finite element analysis. As bone levels diminished, stresses were found to increase dramatically and to concentrate in the small amount of dentin remaining near the post apex.

Alveolar Process↗