This experimental study adopts a fracture mechanics strategy to investigate the mechanical cause of aortic dissection. Inflation of excised healthy bovine aortic rings with a cut longitudinal notch that extends into the media from the intima suggests that an intimal tear may propagate a nearly circumferential-longitudinal rupture surface that is similar to the delamination that occurs in aortic dissection. Radial and 45°-from-radial cut notch orientations, as seen in the thickness surface, produce similar circumferential crack propagation morphologies. Partial cut notches, whose longitudinal length is half the width of the ring, measure the influence of longitudinal material on crack propagation. Such specimens also produce circumferential cracks from the notch root that are visible in the thickness circumferential-radial plane, and often propagate a secondary crack from the base of the notch, visible in the intimal circumferential-longitudinal plane. Inflation of rings with pairs of cut notches demonstrates that a second notch modifies the propagation created in a specimen with a single notch.

The circumferential crack propagation is likely a consequence of the laminar medial structure. These fracture surfaces are probably due to non-uniform circumferential shear deformation in the heterogeneous media as the aortic wall expands. The qualitative deformation morphology around the root of the cut notch during inflation is evidence for such shear deformation. The shear apparently results from relative slip in the circumferential direction of collagen fibers. The slip may produce shear in the longitudinal-circumferential plane between medial layers or in the radial-circumferential plane within a medial lamina in an idealized model. Circumferential crack propagation in the media is then a shear mechanical process that might be facilitated by disease of the tissue.

Statement of Significance

An intimal tear of an apparently healthy aortic wall near the aortic arch is life-threatening because it may lead to full rupture or to wall dissection in which delamination of the medial layer extends around most of the aortic circumference. The mechanical events underlying dissection are not definitively established. This experimental fracture mechanics study provides evidence that shear rupture is the main mechanical process underlying aortic dissection. The commonly performed tensile strength tests of aortic tissue are not clinically useful to predict or describe aortic dissection. One implication of the study is that shear tests might produce more fruitful simple assessments of the aortic wall strength. A clinical implication is that when presented with an intimal tear, those who guide care might recommend steps to reduce the shear load on the aorta.

中文翻译：

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健康牛降主动脉介质中的剪切裂纹扩展和解剖的断裂力学

本实验研究采用骨折力学策略研究主动脉夹层的机械原因。切除的健康牛主动脉环具有从内膜延伸到中膜的切开的纵向凹口，表明内膜撕裂可能会传播近乎周向的纵向破裂表面，这与在主动脉夹层中发生的分层相似。从厚度表面看，径向和与径向成45°的切口方向会产生类似的周向裂纹扩展形态。纵向切口的长度为环的一半，用于测量纵向材料对裂纹扩展的影响。这样的样品还会从缺口的根部产生周向裂纹，这些裂纹在厚度周向径向平面中可见，并且通常会从凹口的底部传播第二个裂纹，在内膜的周向-纵向平面中可见。带有成对切口的环的充气表明，第二个切口会修改带有单个切口的样本中产生的传播。

周向裂纹扩展可能是层状中间结构的结果。这些破裂面可能是由于主动脉壁扩张时，异质介质中的周向剪切变形不均匀所致。膨胀期间切槽根部周围的定性变形形态是这种剪切变形的证据。剪切力显然是由于胶原纤维在圆周方向上的相对滑动而引起的。在理想模型中，滑动可能会在中间层之间的纵向周向平面中或在中间层内的径向周向平面中产生剪切。介质中的周向裂纹扩展是一种剪切机械过程，可能由于组织疾病而变得容易。

重要声明

主动脉弓附近表面健康的主动脉壁的内膜撕裂会危及生命，因为它可能导致完全破裂或壁剥离，其中内侧层的分层会围绕主动脉的大部分周围延伸。解剖的机械事件尚未确定。这项实验性的断裂力学研究提供了证据，即剪切断裂是主动脉夹层的主要力学过程。通常进行的主动脉组织抗张强度测试在临床上无法预测或描述主动脉夹层。该研究的一个含义是，剪切试验可能会对主动脉壁强度进行更有效的简单评估。临床意义是当出现内膜撕裂时，