Active wall tension and passive constitutive relation of the right ventricular free wall

The right ventricle (RV) of the heart plays a vital role in such disorders as pulmonary hypertension, myocardial ischemia, congenital defects, and congestive heart failure. Many important questions on how the RV performs its function still remain. The objective of this dissertation was to extend our knowledge of the mechanical behavior of the right ventricular free wall (RVFW) through both experimental and computational approaches.;The in-vivo surface geometry of the RVFW was reconstructed using ECG-gated MR images of the heart during systole. The complex RVFW differential geometry was quantitatively characterized, using biquadric surface patches and smoothing and refinement processing, in terms of in-surface coordinates. Results showed that while the RVFW undergoes small changes in curvature, its overall shape remained constant during systole. The ratio of wall thickness/mean radius of curvature was less than 0.1 during systole throughout the RVFW, indicating it can be idealized as a thin shell.;Using a thin-walled membrane shell model and the in-vivo geometry, the in-vivo wall tensions at end diastole (ED) and end systole (ES) were computed. The method involved no mechanical coupling to the myocardium, and can account for shear in the myocardium. Results indicated a uniform development of wall tension in the RVFW at both ED and ES, with no regional differences. The direction of major principal tension corresponded closely to the direction of major principal curvature. Overall, the development of active wall tension in the RVFW appears to be rather uniform.;Using excised tissue specimens from the RVFW sub-epicardium, biaxial mechanical experiments were conducted using different stretch protocols, to characterize the myocardium's mechanical response. Specimens were obtained from the conus and sinus to assess regional differences in mechanical properties. The RVFW myocardium was found to be consistently anisotropic, with the fiber direction exhibiting greater stiffness. Further, the anisotropy in the conus region was more pronounced. A comparison with studies of LV midwall myocardium revealed that, (1) the fiber direction stiffnesses were greater in the RVFW than in the LV, (2) the degree of anisotropy is greater in the RVFW than in the LV.