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Comparative Study
. 2009 Apr;49(4):1029-36.
doi: 10.1016/j.jvs.2008.11.056.

Circumferential and Longitudinal Cyclic Strain of the Human Thoracic Aorta: Age-Related Changes

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Free PMC article
Comparative Study

Circumferential and Longitudinal Cyclic Strain of the Human Thoracic Aorta: Age-Related Changes

Tina M Morrison et al. J Vasc Surg. .
Free PMC article

Abstract

Objective: We developed a novel method using anatomic markers along the thoracic aorta to accurately quantify longitudinal and circumferential cyclic strain in nondiseased thoracic aortas during the cardiac cycle and to compute age-related changes of the human thoracic aorta.

Methods: Changes in thoracic aorta cyclic strains were quantified using cardiac-gated computed tomography image data of 14 patients (aged 35 to 80 years) with no visible aortic pathology (aneurysms or dissection). We measured the diameter and circumferential cyclic strain in the arch and descending thoracic aorta (DTA), the longitudinal cyclic strain along the DTA, and changes in arch length and motion of the ascending aorta relative to the DTA. Diameters were computed distal to the left coronary artery, proximal and distal to the brachiocephalic trunk, and distal to the left common carotid, left subclavian, and the first and seventh intercostal arteries. Cyclic strains were computed using the Green-Lagrange strain tensor. Arch length was defined along the vessel centerline from the left coronary artery to the first intercostal artery. The length of the DTA was defined along the vessel centerline from the first to seventh intercostal artery. Longitudinal cyclic strain was quantified as the difference between the systolic and diastolic DTA lengths divided by the diastolic DTA length. Comparisons were made between seven younger (age, 41 +/- 7 years; 5 men) and seven older (age, 68 +/- 6 years; 5 men) patients.

Results: The average increase of diameters of the thoracic aorta was 14% with age from the younger to the older (mean age, 41 vs 68 years) group. The average circumferential cyclic strain of the thoracic aorta decreased by 55% with age from the younger to the older group. The longitudinal cyclic strain decreased with age by 50% from the younger to older group (2.0% +/- 0.4% vs 1.0% +/- 1%, P = .03). The arch length increased by 14% with age from the younger to the older group (134 +/- 17 mm vs 152 +/- 10 mm, P = .03).

Conclusions: The thoracic aorta enlarges circumferentially and axially and deforms significantly less in the circumferential and longitudinal directions with increasing age. To our knowledge, this is the first quantitative description of in vivo longitudinal cyclic strain and length changes for the human thoracic aorta, creating a foundation for standards in reporting data related to in vivo deformation and may have significant implications in endoaortic device design, testing, and stability.

Figures

Figure 1
Figure 1
Above are two volume-rendered thoracic aortas, one from the young (a) and older (b) group. Note the qualitative difference in the curvature of the arch. The older patient has a larger radius of curvature and an increased center line length by approximately 14%.
Figure 2
Figure 2
A partial 3D volume-rendering of the ascending aorta is shown at (a) peak-systole, (b) end-diastole in the Lagrangian frame, and (c) end-diastole in the Eulerian frame. The white line is the segmentation plane aligned at the distal location of the LCA in (a) and (b). In (c), the segmentation plane is fixed at the location from peak-systole, which does not capture the desired lumen boundary. Note that the volume of the left ventricle indicates the stage of the cardiac cycle.
Figure 3
Figure 3
Displayed is a schematic of the thoracic aorta, where the branch vessels are drawn in-plane, which is not typical for patients. (a) The labels for the left coronary artery (LCA), the left subclavian artery (LSC), the first, third and seventh intercostal artery (ICA) are shown. The arch is defined from the LCA to the first ICA, while the DTA is defined from the first to the seventh ICA. The dashed line represents the 3D measurement of the relative deformation between the ascending and descending aorta. (b) The numbers correspond to the locations along the arch and DTA where we quantified circumferential cyclic strain and systolic diameters.
Figure 4
Figure 4
(a) An axial slice of the DTA was captured just distal to an intercostal artery. The white curve, from peak-systole, is super-imposed with the grey curve from end-diastole. Both curves are from the same material location. Notice the circumferential deformation is nonuniform, where the maximum displacement appears to be directly across from a region of minimum vessel displacement near the spine and the ICA. (b) A sagittal slice of the DTA was captured in the middle of the aorta. The white curve, from peak-systole, is super-imposed with the grey curve from end-diastole to highlight the longitudinal motion of the thoracic aorta, where both curves are from the same material location.
Figure 5
Figure 5
The top graph displays the diameters along the thoracic aorta at seven locations. The light and dark shaded bars correspond to the young and older patient populations, respectively. The diameters in the older group are statistically larger that the young group at all locations except for the LCA and BRC. Additionally, the decrease in diameters along the aorta indicates the tapering of the aorta in both populations. The bottom graph displays the circumferential cyclic strain along the thoracic aorta at seven locations. The cyclic strain is significantly smaller in the older patient population and is not statistically different along the length of the aorta in either group.

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