Epicardial Suction: A New Approach to Mechanical Testing of the Passive Ventricular Wall

[+] Author and Article Information
R. J. Okamoto, S. J. Peterson

Department of Mechanical Engineering, Washington University, St. Louis, MO 63130

M. J. Moulton, M. K. Pasque

Division of Cardiothoracic Surgery, Washington University, St. Louis, MO 63130

D. Li

Mallinckrodt Institute of Radiology, Washington University, St. Louis, MO 63130

J. M. Guccione

Department of Mechanical Engineering, Division of Cardiothoracic Surgery, Washington University, St. Louis, MO 63130

J Biomech Eng 122(5), 479-487 (May 30, 2000) (9 pages) doi:10.1115/1.1289625 History: Received April 27, 1999; Revised May 30, 2000
Copyright © 2000 by ASME
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MR tagged images through center of suction cup for experiment 06. (A) and (B): Undeformed short and long-axis images. (C) and (D): Images acquired at t=60 ms, suction pressure=2.3 kPa. (E) and (F): Images acquired at t=105 ms, suction pressure=3.2 kPa.
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Deformed shape plots of FE solution (Exp. 06) with optimized homogeneous material parameters at suction pressure of 3.2 kPa, corresponding to Figs. 5(E) and 5(F). (A) Short-axis view through center of suction cup (B) Long-axis view through center of suction cup.
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Normal (A) and shear (B) strain components as a function of transmural position in FE elements through center of suction cup. (C) Radial-circumferential shear strains in elements through the center of suction cup and to the anterior and posterior of center elements. (D) Radial-longitudinal shear strains in elements through the center of suction cup, and in elements toward the apex and base. All values were predicted from the FE model for experiment 06 using optimized material parameters at experimental pressure of 3.2 kPa as shown in Fig. 6.
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Transmural variation in strain components in FE model of passive LV filling computed at 1 kPa cavity pressure. Lagrangian strain components referred to cardiac coordinates for five experiments were computed at the central gauss point of midventricular elements. Results shown are mean values with one-sided error bars of 1 SD for the model assuming homogeneous, transversely isotropic heart wall (open circles) and transversely isotropic myocardium and isotropic epicardium (open squares). Closed circles with error bars (±1 SD) represent experimental data of Omens et al. 10 on the anterior wall of the LV at midventricle at the same cavity pressure.
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Image planes for MR tagging. In order to acquire a three-dimensional deformation field, five image sequences were obtained in two orthogonal directions with image planes parallel to the walls of the suction cup. Image planes are approximately aligned with the long and short axes of the heart.
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Suction cup with concave surface of nonuniform curvature. The surface was contoured to approximately match the radii of curvature of the lateral free wall of the canine LV.
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Experiment setup, showing: (1) isolated arrested heart in cold saline solution; (2) suction cup; (3) vacuum applied continuously in narrow channel surrounding orifice; (4) servopump; (5) suction pressure measurement; (6) holding fixture and MR orbit coil (cross-hatched). A clamp holding the suction cup in position has been omitted for clarity.
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Overview of the method for optimizing material properties using the epicardial suction. Epicardial suction is applied to a site on the LV. Geometry MR images are used to create an FE model that matches the experimental geometry and location of the suction cup. Measured pressures are used to define the loading for the FE model. Deformed and undeformed tag point locations are used to determine displacements. FE predicted displacements are interpolated from the FE model solution using the deformed tag point locations. At each iteration, the optimization algorithm solves the forward FE problem and calculates the sum of squares of the difference between predicted and measured displacements at all data points. Material parameters in the constitutive relation used in the FE model are adjusted iteratively to minimize the sum of squares objective function.




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