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. 2021 Dec 15;8(12):216.
doi: 10.3390/bioengineering8120216.

The Interventricular Septum Is Biomechanically Distinct from the Ventricular Free Walls

Michael Nguyen-Truong  1 , Wenqiang Liu  1 , Courtney Doherty  1   2 , Kristen LeBar  2 , Kevin M Labus  2 , Christian M Puttlitz  1   2 , Jeremiah Easley  3 , Eric Monnet  3 , Adam Chicco  4 , Zhijie Wang  1   2
Affiliations

The Interventricular Septum Is Biomechanically Distinct from the Ventricular Free Walls

Michael Nguyen-Truong et al. Bioengineering (Basel). .

Abstract

The interventricular septum contributes to the pumping function of both ventricles. However, unlike the ventricular wall, its mechanical behavior remains largely unknown. To fill the knowledge gap, this study aims to characterize the biaxial and transmural variation of the mechanical properties of the septum and compare it to the free walls of the left and right ventricles (LV/RV). Fresh hearts were obtained from healthy, adult sheep. The septal wall was sliced along the mid-line into two septal sides and compared to the epicardial layers of the LV- and RV-free walls. Biaxial tensile mechanical tests and constitutive modeling were performed to obtain the passive mechanical properties of the LV- and RV-side of the septum and ventricular walls. We found that both sides of the septum were significantly softer than the respective ventricular walls, and that the septum presented significantly less collagen than the ventricular walls. At low strains, we observed the symmetric distribution of the fiber orientations and a similar anisotropic behavior between the LV-side and RV-side of the septum, with a stiffer material property in the longitudinal direction, rather than the circumferential direction. At high strains, both sides showed isotropic behavior. Both septal sides had similar intrinsic elasticity, as evidenced by experimental data and constitutive modeling. These new findings offer important knowledge of the biomechanics of the septum wall, which may deepen the understanding of heart physiology.

Keywords: Fung type model; compliance; ovine; septal; transmural difference.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic of orientations for each side of the septum. The arrowhead (longitudinal direction) represents the apex-to-base direction. The black, dashed line square represents the region at which samples were taken for fiber angle measurements and mechanical testing.
Figure 2
Figure 2
Average stress–strain curves of the ventricular free walls (LV, RV) and the LV-side and RV-side of the septum. n = 12 for septum; n = 8 for ventricles. S-LV: LV-side of septum; S-RV: RV-side of septum; L: longitudinal direction; C: circumferential direction.
Figure 3
Figure 3
Comparisons of elastic moduli (M) at low (A,B) and high (C,D) strains from the septal sides and ventricles. Left columns show the M obtained in the longitudinal direction and right columns show the M obtained in the circumferential direction. ** p < 0.01, *** p < 0.001, **** p < 0.0001. n = 10–12 per group for septum; n = 7–8 per group for ventricles. S-LV: LV-side of septum; S-RV: RV-side of septum.
Figure 4
Figure 4
(A,B) Comparison of elastic moduli (M) between biaxial directions in the left and right sides of the septum. Significant anisotropy in both S-LV and S-RV at low strains, and the degree of anisotropy was much stronger in the S-LV. * p < 0.05 vs. circumferential in the same strain range. ** p < 0.01 vs. circumferential in the same strain range. n = 10–12 per group for septum; n = 10–12 per group. S-LV: LV-side of septum; S-RV: RV-side of septum.
Figure 5
Figure 5
Longitudinal (L) and circumferential (C) zero-load elastic modulus (M0) at zero load derived from the fitting parameters for each side of septum. n = 9–11 per group. S-LV: LV-side of septum; S-RV: RV-side of septum.
Figure 6
Figure 6
Representative histology images (left) and the comparisons of collagen area fraction (right) between the S-LV, S-RV, LV, and RV groups. Arrows show the positive staining of collagen fibers. ** p < 0.01, *** p < 0.001. n = 5 per group. S-LV: LV-side of septum; S-RV: RV-side of septum.
See this image and copyright information in PMC

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