Wall stress in media layer of stented three-layered aortic aneurysm at different intraluminal thrombus locations with pulsatile heart cycle

Narrative Review of Risk Assessment of Abdominal Aortic Aneurysm Rupture Based on Biomechanics-Related Morphology

CLINICAL IMPACT

Studies have shown that the biomechanical indicators based on multi-scale models are more effective in accurately assessing the rupture risk of AAA. To meet the need for clinical monitoring and rapid decision making, the typical morphological parameters associated with AAA rupture and their relationships with the mechanical environment have been summarized, which provide a reference for clinical preoperative risk assessment of AAA.

Diagnostic potential of soluble ST2 and D-dimer for Stanford Type B aortic dissection and intramural aortic hematoma

OBJECTIVE

Type B aortic dissection (TBAD) and intramural aortic hematoma (IMH) are common manifestations of Acute Aortic Syndrome (AAS), exhibiting overlapping clinical features. The timely and accurate diagnosis and differentiation between TBAD and IMH are critical for appropriate management. Tumorigenicity 2 (sST2) and D-dimer have been shown to elevate levels in both TBAD and IMH, making them valuable as "rule-out" markers. Hence, we aimed to assess the diagnostic utility of sST2 and D-dimer in distinguishing TBAD from IMH.

METHODS

In this retrospective study, we analyzed serum levels of sST2 and D-dimer in 182 AAS patients, comprising 90 TBAD cases, 92 IMH cases, and 90 non-AAS cases. Serial measurements were taken at 1 h, 6 h, 12 h, 24 h, and 72 h post-admission. Comparative analyses were conducted between TBAD and non-AAS cases, IMH and non-AAS cases, and TBAD and IMH cases. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic accuracy of sST2 and D-dimer in identifying TBAD or IMH cases.

RESULTS

Both TBAD and IMH patients displayed elevated levels of sST2 and D-dimer compared to non-AAS cases. Notably, sST2 levels were significantly higher in TBAD patients than in IMH patients, whereas D-dimer levels exhibited moderate differences. TBAD patients tended to exhibit elevated levels of either sST2 or D-dimer, with a modest correlation between the two (Pearson correlation coefficient = 0.3614). In contrast, IMH patients showed elevations in both markers, with a positive correlation between them (Pearson correlation coefficient = 0.6814). The ROC analysis revealed that both sST2 (AUC, 0.657; 95 % CI, 0.552-0.753; cutoff value, 27.54 ng/ml) and D-dimer (AUC, 0.695; 95 % CI, 0.591-0.787, cutoff value, 1.215 ng/ml) demonstrated favorable diagnostic performance for TBAD. sST2 exhibited a sensitivity of 80.92 % and a specificity of 75.00 %, while D-dimer showed a sensitivity of 80.92 % and a specificity of 75.00 %. For the diagnosis of IMH, the combined assessment of sST2 and D-dimer (AUC, 0.674; 95 % CI, 0.599-0.768; sensitivity, 69.20 %; specificity, 80.00 %) proved effective.

CONCLUSIONS

Our results indicate that both sST2 and D-dimer show diagnostic potential for TBAD. Elevated levels of either serve as an indicator of TBAD onset. However, concurrent elevation of both markers seems to be indicative of IMH. The combination of increased sST2 and D-dimer levels demonstrates strong diagnostic performance in identifying IMH cases.

High-density thrombus and maximum transverse diameter on multi-spiral computed tomography angiography combine to predict abdominal aortic aneurysm rupture

Objective

We attempted to measure maximum transverse diameter (MTD) of and CT values of ILT by using multi-spiral computed tomography angiography (MSCTA) to investigate the predictive value of MTD with different CT values of thrombus on the risk of AAA rupture.

Methods

Forty-five intact abdominal aortic aneurysms (IAAA) and 17 ruptured abdominal aortic aneurysms (RAAA) were included in this study. MTD and CT values in their planes were measured from MSCTA images and aneurysm lumen and thrombus volumes were calculated for the range of different CT values.

Results

The median of maximum CT value of thrombus at the plane of MTD was higher in RAAA (107.0 HU) than the median in IAAA (84.5 HU) (P < 0.001). Univariate logistic regression analysis showed that the maximum CT value was a risk factor for RAAA (P < 0.001). It was further found that the area under the ROC curve for thrombus maximum CT value in the MTD plane to predict RAAA was 0.848 (P < 0.001), with a cut-off value of 97.5 HU, a sensitivity of 82.35%, and a specificity of 84.44%. And the MTD of the abnormal lumen combined with the maximum CT value at its plane predicted RAAA with an area under the ROC curve of 0.901, a sensitivity of 76.47%, and a specificity of 97.78%. The further analysis of thrombus volume in the range of different CT value showed that median thrombus volume in RAAA in the range of 30 HU~150 HU was 124.2 cm³ which was higher than the median of 81.4 cm³ in IAAA (P = 0.005). To exclude confounding factors (aneurysm volume), we calculated the standardized thrombus (ILT volume/total aneurysm volume), and the thrombus volume in the range of 30 HU~150 HU in RAAA was positively correlated with the standardized thrombus volume (ρ = 0.885, P < 0.001), while the thrombus volume in the range of −100 HU~30 HU was not correlated with it (ρ = 0.309, P = 0.228).

Conclusions

High-density ILT shown on MSCTA in AAAs is associated with aneurysm rupture, and its maximum transverse diameter combined with the maximum CT value in its plane is a better predictor of RAAA.

A computational fluid-structure interaction model to predict the biomechanical properties of the artificial functionally graded aorta

In the present study, three layers of the ascending aorta in respect to the time and space at various blood pressures have been simulated. Two well-known commercial finite element (FE) software have used to be able to provide a range of reliable numerical results while independent on the software type. The radial displacement compared with the time as well as the peripheral stress and von Mises stress of the aorta have calculated. The aorta model was validated using the differential quadrature method (DQM) solution and, then, in order to design functionally graded materials (FGMs) with different heterogeneous indexes for the artificial vessel, two different materials have been employed. Fluid-structure interaction (FSI) simulation has been carried out on the FGM and a natural vessel of the human body. The heterogeneous index defines the variation of the length in a function. The blood pressure was considered to be a function of both the time and location. Finally, the response characteristics of functionally graded biomaterials (FGBMs) models with different values of heterogeneous material parameters were determined and compared with the behaviour of a natural vessel. The results showed a very good agreement between the numerical findings of the FGM materials and that of the natural vessel. The findings of the present study may have implications not only to understand the performance of different FGMs in bearing the stress and deformation in comparison with the natural human vessels, but also to provide information for the biomaterials expert to be able to select a suitable material as an implant for the aorta.

A combination of experimental and numerical methods to investigate the role of strain rate on the mechanical properties and collagen fiber orientations of the healthy and atherosclerotic human coronary arteries

Atherosclerosis enables to alter not only the microstructural but also the physical properties of the arterial walls by plaque forming. Few studies so far have been conducted to calculate the isotropic or anisotropic mechanical properties of the healthy and atherosclerotic human coronary arteries. To date there is a paucity of knowledge on the mechanical response of the arteries under different strain rates. Therefore, the objective of the concurrent research was to comprehend whether the alteration in the strain rates of the human atherosclerotic arteries in comparison with the healthy ones contribute to the biomechanical behaviors. To do this, healthy and atherosclerotic human coronary arteries were removed from 18 individuals during autopsy. Histological analyses by both an expert histopathologist and an imaged-based recognizer software were performed to figure out the average angle of collagen fibers in the healthy and atherosclerotic arterial walls. Thereafter, the samples were subjected to 3 diverse strain rates, i.e., 5, 20, and 50 mm/min, until the material failure occurs. The stress-strain diagrams of the arterial tissues were calculated in order to capture their linear elastic and nonlinear hyperelastic mechanical properties. In addition, Artificial Neural Networks (ANNs) was employed to predict the alteration of mean angle of collagen fibers during load bearing up to failure. The findings suggest that strain rate has a significant (p < 0.05) role in the linear elastic and nonlinear hyperelastic mechanical properties as well as the mean angle of collagen fibers of the atherosclerotic arteries, whereas no specific impact on the healthy ones. Furthermore, the mean angle of collagen fibers during the load bearing up to the failure at each strain rate was well predicted by the proposed ANNs code.

A comparative study on the mechanical properties of the healthy and varicose human saphenous vein under uniaxial loading

Saphenous Vein (SV) due to fatness, age, inactiveness, etc. can be afflicted with varicose. The main reason of the varicose vein is believed to be related to the leg muscle pump which is unable to return the blood to the heart in contradiction of the effect of gravity. As a result of the varicose vein, both the structure and mechanical properties of the vein wall would alter. However, so far there is a lack of knowledge on the mechanical properties of the varicose vein. In this study, a comparative study was carried out to measure the elastic and hyperelastic mechanical properties of the healthy and varicose SVs. Healthy and varicose SVs were removed at autopsy and surgery from seven individuals and then axial tensile load was applied to them up to the failure point. In order to investigate the mechanical behaviour of the vein, this study was benefitted from three different stress definitions, such as 2nd Piola-Kichhoff, engineering and true stresses and four different strain definitions, i.e. Almansi-Hamel, Green-St. Venant, engineering and true strains, to determine the linear mechanical properties of the SVs. A Digital Image Correlation (DIC) technique was used to measure the true strain of the vein walls during load bearing. The non-linear mechanical behaviour of the SVs was also computationally evaluated via the Mooney-Rivlin material model. The true/Cauchy stress-strain diagram exhibited the elastic modulus of the varicose SVs as 45.11% lower than that of the healthy ones. Furthermore, by variation of the stress a significant alteration on the maximum stress of the healthy SVs was observed, but then not for the varicose veins. Additionally, the highest stresses of 4.99 and 0.65 MPa were observed for the healthy and varicose SVs, respectively. These results indicate a weakness in the mechanical strength of the SV when it becomes varicose, owing to the degradation of the elastin and collagen content of the SV. The Mooney-Rivlin hyperelastic and the Finite Element (FE) data were finally well compared to the experimental data.