Artery Research (Dec 2020)

P.08 Biomechanical Characterization of Ascending Thoracic Aortic Aneurysms in Humans: A Continuum Approach to in vivo Deformations

  • Shaiv Parikh,
  • Bart Spronck,
  • Gijs Debeij,
  • Berta Ganizada,
  • Mitch Ramaekers,
  • Simon Schalla,
  • Ehsan Natour,
  • Jos Maessen,
  • Tammo Delhaas,
  • Wouter Huberts,
  • Elham Bidar,
  • Koen Reesink

DOI
https://doi.org/10.2991/artres.k.201209.022
Journal volume & issue
Vol. 26, no. Supplement 1

Abstract

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Background: Dysfunctional cellular mechanosensing appears central to aneurysm formation [1]. We aimed to derive material parameters of aneurysm tissue from in vivo deformations, which may increase insight into the underlying structural integrity of the pathological tissue. Methods: Videos of tracking markers (example Video in supplement, screenshot in Figure) placed on ascending aortic segments were captured alongside radial arterial blood pressure in patients undergoing open-thorax ascending thoracic aorta aneurysm (ATAA) repair (n = 5) and coronary bypass (controls; n = 2). Normalised cross-correlation was used to determine marker displacements, resulting in estimates of systolic/diastolic diameters, distensibility, and cyclic axial engineering strain. A thin-walled, cylindrical geometry was assumed, with amorphous (Neo-Hookean) and fibrous (two-family) constitutive contributions [2]. This framework was fitted to individual patient measurements, by varying parameters c (amorphous material constant), k1 and k2 (fiber stiffness and strain stiffening parameter), β (fiber angle w.r.t. circumferential direction), unloaded intact length (L), and internal radius (Ri). FigureLeft: Example of ascending aortic region of interest with tracking markers. Right: Data presented as mean ± standard deviation. SBP/DBP, systolic/diastolic blood pressure. Estimated properties are defined in the text. Results: Axial strain tended to be lower (expected) and distensibility larger (unexpected) in aneurysm than controls (Figure). However, the intrinsic pressure-dependence of distensibility must be considered when drawing conclusions related to differences in structural stiffness between both groups [3]. Material stiffness parameters (c and k1) appeared higher in aneurysm patients than in controls which is in line with previous studies in mice [4]. Conclusion: We are developing a method to determine ATAA material properties from in vivo deformations and observed increased material stiffness in ATAA.

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