Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Determination of Cross-directional and Cross-Wall Variations of Passive Biaxial Mechanical Properties of Rat Myocardium

Version 1 : Received: 11 September 2021 / Approved: 14 September 2021 / Online: 14 September 2021 (15:12:23 CEST)

How to cite: Ngwangwa, H.; Nemavhola, F.; Pandelani, T.; Msibi, M.; Mabuda, I.; Davies, N.; Franz, T. Determination of Cross-directional and Cross-Wall Variations of Passive Biaxial Mechanical Properties of Rat Myocardium. Preprints 2021, 2021090244 (doi: 10.20944/preprints202109.0244.v1). Ngwangwa, H.; Nemavhola, F.; Pandelani, T.; Msibi, M.; Mabuda, I.; Davies, N.; Franz, T. Determination of Cross-directional and Cross-Wall Variations of Passive Biaxial Mechanical Properties of Rat Myocardium. Preprints 2021, 2021090244 (doi: 10.20944/preprints202109.0244.v1).

Abstract

Heart myocardia are critical to the facilitation of heart pumping and blood circulating around the body. The biaxial mechanical testing of the Left Ventricle (RV) is utilised to build the computa-tional model of the whole heart with little importance given to the unique mechanical properties of Right Ventricle (RV) and Mid-wall (MDW). Most of those studies focussed on the LV of the heart, and then apply the obtained characteristics with a few modifications to the right side of the heart. However, that view has been contested over time with the realisation that the right side of the heart possesses its own unique mechanical properties that are widely distinct from that of the left side of the heart. This paper is aimed at reporting and evaluating the passive mechanical property dif-ferences in the three main walls of the rat heart based on biaxial tensile test data. Fifteen mature Wistar rats weighing 225 ± 25 g were euthanised by inhalation of 5 % halothane. The hearts were excised after which all the top chambers comprising the two atria, pulmonary and vena cava trunks, aorta and valves are all dissected out. Then 5 x 5 mm sections from the middle of each wall were carefully dissected with a surgical knife to avoid over-prestraining the specimens. The specimens were subjected tensile test. The elastic moduli, peak stresses in the toe region and stresses at 40 % strain, anisotropy indices as well as the stored strain energy in the toe and linear region up to 40 % strain are used for statistical significance tests. The following are the main findings of this study: (1) LV and MDW tissues have relatively shorter toe regions of 10 - 15 % strain as compared to RV tissue whose toe region extends up to twice as much as that (2) LV tissues have higher strain energy storage in the linear region despite being lower in stiffness than the RV (3) the MDW has the highest strain energy storage along both directions which might be directly related to its high level of anisotropy. These findings, though for a specific animal species at similar age and around the same body mass, emphasize the importance of application of wall specific material parameters to obtain accurate ventricular hyperelastic models. The findings further enhance our understanding of the desired mechanical behaviour of the different ventricle walls.

Keywords

Myocardium tissue; Left ventricle mechanics; right ventricle mechanics; cardiac septum mechanics; anisotropy index

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