Effect of Laminar Orthotropic Myofiber Architecture on Regional Stress and Strain in the Canine Left Ventricle |
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Authors: | TP Usyk R Mazhari AD McCulloch |
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Institution: | (1) Department of Bioengineering, The Whitaker Institute for Biomedical Engineering, University of California, San Diego, La Jolla, Calif., U.S.A.;(2) Department of Bioengineering, The Whitaker Institute for Biomedical Engineering, University of California, San Diego, La Jolla, Calif., U.S.A. |
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Abstract: | Recent morphological studies have demonstrated a laminar (sheet) organization of ventricular myofibers. Multiaxial measurements
of orthotropic myocardial constitutive properties have not been reported, but regional distributions of three-dimensional
diastolic and systolic strains relative to fiber and sheet axes have recently been measured in the dog heart by Takayama et
al. 30]. A three-dimensional finite-deformation, finite element model was used to investigate the effects of material orthotropy
on regional mechanics in the canine left ventricular wall at end-diastole and end-systole. The prolate spheroidal model incorporated
measured transmural distributions of fiber and sheet angles at the base and apex. Compared with transverse isotropy, the orthotropic
model of passive myocardial properties yielded improved agreement with measured end-diastolic strains when: (1) normal stiffness
transverse to the muscle fibers was increased tangent to the sheets and decreased normal to them; (2) shear coefficients were
increased within sheet planes and decreased transverse to them. For end-systole, orthotropic passive properties had little
effect, but three-dimensional systolic shear strain distributions were more accurately predicted by a model in which significant
active systolic stresses were developed in directions transverse to the mean fiber axis as well as axial to them. Thus the
ventricular laminar architecture may give rise to anisotropic material properties transverse to the fibers with greater resting
stiffness within than between myocardial laminae. There is also evidence that intact ventricular muscle develops significant
transverse stress during systole, though it remains to be seen if active stress is also orthotropic with respect to the laminar
architecture.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | myocardium myofibers constitutive equation and orthotropy |
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