Sokolis Dimitrios P, Ch Markidi Despoina, Iliopoulos Dimitrios C, Kourkoulis Stavros K
Laboratory of Biomechanics, Center of Clinical, Experimental Surgery, and Translational Research, Biomedical Research Foundation of the Academy of Athens, Athens, Greece.
Department of Mechanics, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Athens, Greece.
J Biomech. 2023 Jan;147:111432. doi: 10.1016/j.jbiomech.2023.111432. Epub 2023 Jan 5.
The stress distribution in ascending thoracic aortic aneurysms is determined by the mechanical properties, geometry, loading conditions, and zero-stress state of the aneurysmal aorta. Our objective was to fully characterize the zero-stress state of the aneurysmal aorta in twelve tricuspid aortic valve patients and eight (age/aortic diameter-matched) bicuspid aortic valve patients, for which little data are available. Opening angles and residual stretches were measured for the intact wall and individual layers according to quadrant and were similar in the two patient groups. The intact-wall and medial opening angles were comparable; their circumferential but not their axial ones peaked in the left lateral quadrant, with non-significant regional differences in the other layers. The intima's circumferential opening angles were the highest of all layers (∼300 deg) and the adventitia's the lowest (∼165 deg), with lesser layer differences in the axial opening angles. Upon radially cutting aortic rings, the released circumferential residual stretches were tensile (of large magnitude) externally and compressive (of small magnitude) internally, unlike the axial residual stretches released when cutting intact-wall strips, whose magnitude was small externally and large internally. Nevertheless, large circumferential compressive residual stretches were released in the adventitia upon layer dissection, counteracting the large circumferential tensile stretches of the intact wall externally. Moreover, the large axial tensile residual stretches of the intima counteracted the large axial compressive stretches of the intact wall internally. These layer-specific residual stretches may moderate the in-vivo stress gradients across wall thickness, serving as a protective mechanism against aortic dissection or rupture.
升主动脉瘤的应力分布由瘤性主动脉的力学性能、几何形状、负荷条件和零应力状态决定。我们的目标是全面表征12例三尖瓣主动脉瓣患者和8例（年龄/主动脉直径匹配）二尖瓣主动脉瓣患者瘤性主动脉的零应力状态，目前关于这方面的数据很少。根据象限测量完整壁和各层的开口角度及残余伸长，两组患者的结果相似。完整壁和中层的开口角度相当；它们的周向开口角度在左侧象限达到峰值，而轴向开口角度并非如此，其他层的区域差异不显著。内膜的周向开口角度在所有层中最高（约300度），外膜的最低（约165度），轴向开口角度的层间差异较小。在对主动脉环进行径向切割时，释放的周向残余伸长在外部是拉伸的（幅度较大），在内部是压缩的（幅度较小），这与切割完整壁条带时释放的轴向残余伸长不同，后者在外部幅度较小，在内部幅度较大。然而，在进行层间解剖时，外膜释放出较大的周向压缩残余伸长，在外部抵消了完整壁的大周向拉伸伸长。此外，内膜的大轴向拉伸残余伸长在内部抵消了完整壁的大轴向压缩伸长。这些特定层的残余伸长可能会缓和体内跨壁厚的应力梯度，起到防止主动脉夹层或破裂的保护机制作用。
