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Research Papers

Impact of Weightlessness on Cardiac Shape and Left Ventricular Stress/Strain Distributions

[+] Author and Article Information
Ilana Iskovitz

Senior Scientist
e-mail: Ilana.Iskovitz@nasa.gov

Mohammad Kassemi

Mem. ASME
Chief Scientist
e-mail: Mohammad.Kassemi@nasa.gov
National Center for Space Exploration Research (NCSER),
NASA Glenn Research Center,
Cleveland, OH 44135

James D. Thomas

Department of Cardiovascular Medicine,
Cleveland Clinic Foundation,
9500 Euclid Avenue J1-5,
Cleveland, OH 44195

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received January 29, 2013; final manuscript received September 10, 2013; accepted manuscript posted September 9, 2013; published online October 24, 2013. Assoc. Editor: Jeffrey W. Holmes.

J Biomech Eng 135(12), 121008 (Oct 24, 2013) (11 pages) Paper No: BIO-13-1053; doi: 10.1115/1.4025464 History: Received January 29, 2013; Accepted September 09, 2013; Revised September 10, 2013

In this paper, a finite element model of the heart is developed to investigate the impact of different gravitational loadings of Earth, Mars, Moon, and microgravity on the cardiac shape and strain/stress distributions in the left ventricle. The finite element model is based on realistic 3D heart geometry, detailed fiber/sheet micro-architecture, and a validated orthotropic cardiac tissue model and constitutive relationship that capture the passive behavior of the heart at end-diastole. The model predicts the trend and magnitude of cardiac shape change at different gravitational levels with great fidelity in comparison to recent cardiac sphericity measurements performed during simulated reduced-gravity parabolic flight experiments. Moreover, the numerical predictions indicate that although the left ventricular strain distributions remain relatively unaltered across the gravitational fields and the strain extrema values occur at the same relative locations, their values change noticeably with decreasing gravity. As for the stress, however, both the magnitude and location of the extrema change with a decrease in the gravitational field. Consequently, tension regions of the heart on Earth can change into compression regions in space.

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Figures

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Fig. 1

The 3D heart geometry: LV anterior, free-wall, posterior, and septum zones shown with respect to the global reference coordinate system XYZ (a), the whole heart structure (b), and the side (c) and top (d) views of the heart finite element mesh displaying the left and right ventricle cavities.

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Fig. 2

Validation of the orthotropic material model: Comparison of the Finite element models predictions with: (a) shear test [30], (b) uniaxial test [37], and (c) intact heart inflation experiments [38,39]

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Fig. 3

(a) Echocadiographic image indicating the location of the measured sphericity dimensions, (b) Numerical prediction of gravitational impact on cardiac sphericity (H/W) in comparison to the parabolic flight experimental measurements (Summers et al. [10]). R1 and R2 plots correspond to two different locations of W as shown in the insert schematic.

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Fig. 4

(a) LV sphericity as a function of LV pressure, (b) contours of the difference in cardiac deformation between 1 g and μg for three LV pressure levels

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Fig. 5

Distribution of major principal strain value, E1, within the LV anterior surface for the four gravitational levels and a LV ventricular pressure of 1 kPa. Bullet points mark the locations of maximum (P-8397) and minimum (P-642) strain values. For most of the LV surface, the strain is within the range 0.25–0.40.

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Fig. 6

Major (a) and minor (b) principal strains (E1 and E3) as a function of normalized gravity for a LV ventricular pressure of 1 kPa. Numbered bullets mark the extrema locations where the data were extracted.

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Fig. 7

Distribution of the major principal stress, S1, in the LV septum for a ventricular pressure of 1 kPa: localized extrema values in the red contour regions are listed on the cases' legend. Compression areas are depicted via gray shading.

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Fig. 8

Major principal stress values (for a LV ventricular pressure of 1 kPa) as a function of normalized gravity at the extrema locations depicted on the side sketch: (a) P-7456 and P-6456, (b) P-13753, and (c) variation of S1 at location P-8518 as a function of LV pressure (note that the 1 g results were simulated by ramping up gravity to its desired final value during the first ten pseudotime increments and then keeping it constant during the rest of the simulation).

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Fig. 9

Scaled compression distribution for minor principal stress, S3, within the LV free wall with a ventricular pressure of 1 kPa. The extreme stress values are quite localized (around P-7456). Most of the structure is under uniform stress as depicted in blue.

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