Insights of right ventricular anisotropic hysteresis behavior with pulmonary hypertension development

There is growing evidence of myocardial hysteresis and, recently, the viscoelasticity of healthy and pulmonary hypertensive (PH) right ventricle free walls (RVFW) has been studied by stress-relaxation. However, stress-relaxation does not fully capture thein vivodeformation of the tissue, and the changes in right ventricle hysteresis behavior with PH remain unknown. Our aim was to investigate RVFW biaxial hysteresis behavior with PH. We conducted equibiaxial cyclic sinusoidal tensile testing in healthy and PH rat RVFW tissues under 20% strain, with strain rates of 0.1&1 Hz (sub-physiological), and 5&8 Hz (physiological). Elastic modulus, loop height, stored and dissipated energies, the ratio of viscosity to elasticity (V/E), and the percentage of dissipated to total energy (damping) were derived. After PH, elastic modulus was elevated in both directions, while longitudinal loop height and stored and dissipated energies were increased (p< 0.05). Despite these individual changes in viscosity and elasticity, V/E ratio and damping were maintained. We further found frequency-dependent responses of V/E ratio and damping, and these were enhanced in the diseased RVs (p< 0.05 at 5&8 Hz) than healthy RVs (p< 0.05 only at 8 Hz). Finally, we observed significant correlations between individual mechanical properties and structural changes (collagen content/myofiber width), and the correlations were stronger in the longitudinal (p⩽ 0.006) than circumferential (p< 0.05) direction. Moreover, collagen had a much greater contribution (p⩽ 0.002) to tissue elasticity than myofiber (p⩽ 0.02). Multiple linear regression analyses revealed a significant role of myofibers, not collagen content, in the tissue viscosity in both directions (p< 0.05). Our results suggest the importance of incorporating tissue viscoelastic properties into pathophysiology as well as the design of cardiac biomimetic materials for advancements in cardiac health.