Cardiovascular Engineering and Technology最新文献

Purpose: It is known that elastic laminae (ELs) in the aortic wall, especially the inner layers, are structurally buckled due to residual stresses under unpressurized conditions. Herein, we aimed to develop a realistic computational model, replicating the mechanical behavior of an aortic ring from no-load to physiological conditions by considering inherent residual stresses, which has not been widely included in conventional modeling studies.

Methods: We determined specific conditions to reproduce EL buckling with a "preferable" residual stress distribution under no-load conditions by combining the design of experiments and multiobjective optimization. Subsequently, we applied these conditions to two ring models with distinct wall structures comprised ELs and smooth muscle layers (SMLs), and compared their mechanical responses to assess the effect of implemented residual stresses by tracking changes in stress distribution in the aortic wall and corresponding EL waviness under no-load and pressurized conditions.

Results: We successfully reproduced EL buckling with a steady upward residual stress distribution that was considered "preferable" under no-load conditions. Furthermore, we replicated radially cut ring models that spontaneously opened in vitro, and confirmed that an SML circumferential stress distribution approached a uniform state under pressurized conditions, effectively mediating stress concentrations induced at the inner layers.

Conclusions: We established a ready-to-use scheme to implement intrinsic residual stresses in the aortic wall. Our computational model of the aortic ring, reproducing realistic mechanical responses and behavior, represents a valuable tool that offers essential insights for hypertension prevention and potential new clinical applications.

Purpose: Cardiovascular simulators are used in the preclinical testing phase of medical devices. Their reliability increases the more they resemble clinically relevant scenarios. In this study, a physiologically actuated soft robotic left ventricle (SRLV) embedded in a hybrid (in silico- in vitro) simulator of the cardiovascular system is presented, along with its experimental and computational analysis.

Methods: A SRLV phantom, developed from a patient's CT scan using polyvinyl alcohol (PVA), is embedded in a hybrid cardiovascular simulator. We present an activation method in which the hydraulic pressure external ( $P_e\left(t\right)$ ) to the SRLV is continuously adapted to regulate the left ventricular volume ( $V_i\left(t\right)$ ), considering the geometry and material behavior of the SRLV and the left ventricular pressure ( $P_i\left(t\right)$ ). This activation method is verified using a finite element (FE) model of the SRLV and validated in the hybrid simulator. Different hemodynamic profiles are presented to test the flexibility of the method.

Results: Both the FE model and hybrid simulator could represent the desired in silico data ( $P_i\left(t\right)$ , $V_i\left(t\right)$ ) with the implemented activation method, with deviations below 8.09% in the FE model and mainly < 10% errors in the hybrid simulator. Only two measurements out of 32 exceeded the 10% threshold due to simulator setup limitations.

Conclusion: The activation method effectively allows to represent various pressure-volume loops, as verified numerically, and validated experimentally in the hybrid simulator. This work presents a high-fidelity platform designed to simulate cardiovascular conditions, offering a robust foundation for future testing of cardiovascular medical devices under physiological conditions.

These findings provide significant implications for the enhancement of iliac vein stent implantation strategies and stent design. The prevalent use of stents for treating Iliac Vein Compression Syndrome (IVCS) has shown efficacy, yet the associated clinical adverse events, including stent restenosis and postoperative thrombosis, are significant concerns. Up to now, the mechanism how the stent implantation induces the restenosis and DVT is still unclear. Our study hypothesizes that these adverse outcomes arise from altered blood flow dynamics following stent implantation. Employing computational modeling and medical imaging, we simulated IVCS after various stenting procedures to assess their impact on venous blood flow characteristics, including wall shear stress (WSS), residence time (RRT), and oscillatory shear index (OSI). Our findings reveal that a stent protruding into the vena cava impedes blood circulation, with increased protrusion exacerbating this obstruction. This is particularly evident at the vein bifurcation, where low WSS and elevated OSI and RRT are observed. Moreover, a higher stent strut density further obstructs blood flow, deteriorating the hemodynamic environment. Consequently, stent protrusion into the vena cava can enhance the likelihood of adverse post-surgical events. These insights have profound implications for optimizing iliac vein stent implantation techniques and stent design.

Introduction: An abdominal aortic aneurysm (AAA) is a dilation localized in the infrarenal segment of the abdominal aorta that can expand continuously and rupture if left untreated. Computational methods such as finite element analysis (FEA) are widely used with in silico models to calculate biomechanical predictors of rupture risk while choosing constitutive material properties for the AAA wall and intraluminal thrombus (ILT).

Methods: In the present work, we investigated the effect of different constitutive material properties for the wall and ILT on 21 idealized and 10 unruptured patient-specific AAA geometries. Three material properties were used to characterize the wall and two for the ILT, leading to six material model combinations for each AAA geometry subject to appropriate boundary conditions.

Results: The results of the FEA simulations indicate significant differences in the average peak wall stress (PWS), 99th percentile wall stress (99th WS), and spatially averaged wall stress (SAWS) for all AAA geometries subject to the choice of a material model combination. Specifically, using a material model combination with a compliant ILT yielded statistically higher wall stresses compared to using a stiff ILT, irrespective of the constitutive equation used to model the AAA wall.

Discussion: This work provides quantitative insight into the variability of the wall stress distributions ensuing from AAA FEA modeling due to its strong dependency on population-averaged soft tissue material characterizations. This dependency leads to uncertainty about the true biomechanical state of stress of an individual AAA and the subsequent assessment of its rupture risk.

Purpose: The initiation of intracranial aneurysms has long been studied, mainly by the evaluation of the wall shear stress field. However, the debate about the emergence of hemodynamic stimuli still persists. This paper builds on our previous hypothesis that secondary flows play an important role in the formation cascade by examining the relationship between flow physics and vessel geometry.

Methods: A composite evaluation framework was developed to analyze the simulated flow field in perpendicular cross-sections along the arterial centerline. The velocity field was decomposed into secondary flow components around the centerline in these cross-sections, allowing the direct comparison of the flow features with the geometrical parameters of the centerline. Qualitative and statistical analysis was performed to identify links between morphology, flow, and the formation site of the aneurysms.

Results: The normalized mean curvature and curvature peak were significantly higher in the aneurysmal bends than in other arterial bends. Similarly, a significant difference was found for the normalized mean velocity ( $p=0.0274$ ), the circumferential ( $p=0.0029$ ), and radial ( $p=0.0057$ ) velocity components between the arterial bends harboring the aneurysm than in other arterial bends. In contrast, the difference of means for the normalized axial velocity is insignificant ( $p=0.1471$ ).

Conclusion: Thirty cases with aneurysms located on the ICA were analyzed in the virtually reconstructed pre-aneurysmal state by an in-silico study. We found that sidewall aneurysm formation on the ICA is more probable in these arterial bends with the highest case-specific curvature, which are accompanied by the highest case-specific secondary flows (circumferential and radial velocity components) than in other bends.

Purpose: Atrial fibrillation (AF) is the most common chronic cardiac arrhythmia that increases the risk of stroke, primarily due to thrombus formation in the left atrial appendage (LAA). Left atrial appendage occlusion (LAAO) devices offer an alternative to oral anticoagulation for stroke prevention. However, the complex and variable anatomy of the LAA presents significant challenges to device design and deployment. Current benchtop models fail to replicate both anatomical variability and physiological hemodynamics, limiting their utility. This study introduces a novel left atrial cardiac simulator that incorporates patient-derived LAA models within a benchtop circulatory flow loop, enabling high-fidelity LAAO device testing and development.

Methods: A rigid, patient-derived left atrium (LA) model was 3D printed from segmented MRI data and modified to accommodate attachment of patient-specific LAA models. A library of LAA geometries was fabricated using silicone casting techniques to replicate the mechanical properties of native tissue. The LA-LAA model was integrated into a circulatory flow loop equipped with a pulsatile pump, pressure sensors, and flow probes, allowing real-time hemodynamic analysis. System tunability was demonstrated by varying heart rate, stroke volume, resistance, and compliance to simulate physiological and pathological conditions.

Results: The simulator accurately replicated LA pressure and flow waveforms, closely approximating physiological conditions. Changes in heart rate, stroke volume, and compliance effectively modulated LAP and LA inflow before and after LAAO. Distinct pressure and flow waveforms were observed with different LAA geometries. Hemodynamic analysis revealed increased left atrial pulse pressure after occlusion, with the greatest increase occurring after complete exclusion of the LAA. The simulator facilitated the evaluation of LAAO device performance, including metrics such as seal and PDL, and served as an effective training tool for iterative device deployment and recapture with visual and imaging-guided feedback.

Conclusions: The left atrial cardiac simulator offers a highly tunable and realistic platform for testing and developing LAAO devices. It also serves as an effective procedural training tool, allowing for the simulation of patient-specific anatomical and hemodynamic conditions. By enabling these advanced simulations, the simulator enhances pre-procedural planning, device sizing, and placement. This innovation represents a significant step toward advancing personalized medicine in atrial fibrillation management and improving LAAO outcomes.

Purpose: Dysfunction of vasomotor reactions due to arteriolar smooth muscle causes serious adverse events, such as loss of hemodynamic coherence. This in turn can increase risks of cardiovascular-related diseases. A noninvasive and quantitative evaluation of microvascular disorder is therefore very important for early diagnosis and treatment. This paper describes a new approach to the assessment of vasomotor functions using the arteriolar elasticity measurement technique in the fingertip.

Methods: A recently developed device, modified to detect a photoplethysmogram with green light (gPPG) in arteriolar regions, allowed the measurement of arteriolar blood pressure (BP_ca.) and gPPG from a left index fingertip placed on an occlusive cuff of the device. Arteriolar stiffness and distensibility were analyzed as effective elasticity indices, as a function of arteriolar distending pressure derived by volume-oscillometry. Cold pressor tests to induce vasoconstriction were carried out whether appropriate elasticity changes could be obtained.

Results: Experiments using 6 healthy subjects were successfully made to obtain arteriolar elastic properties before and while immersing a right hand in cold water. The index-values of stiffness and distensibility showed, respectively, a considerable increase and decrease, clearly demonstrating the appropriate elasticity changes with vasoconstrictive reactions.

Conclusion: Although a further study using many subjects is needed, the results so far suggest that this method could easily provide important features to acquire quantitatively arteriolar elasticity together with BP_ca. and to assess vasomotor functions in the microvasculature. This convenient method appears useful for clinical practices and health management and promising also for screening cardiovascular-related diseases. (242/250 words).

Purpose: Over time, transit time flow measurement (TTFM) has proven itself as a simple and effective tool for intra-operative evaluation of coronary artery bypass grafts (CABGs). However, metrics used to screen for possible technical error show considerable spread, preventing the definition of sharp cut-off values to distinguish between patent, questionable, and failed grafts. The simulation study presented in this paper aims to quantify this uncertainty for commonly used patency metrics, and to identify the most important physiological parameters influencing it.

Methods: Uncertainty quantification was performed on a realistic multiscale numerical model of the coronary circulation, guided by Morris screening sensitivity analysis of a simpler, lumped-parameter model. Simulation results were qualitatively verified against results of a recent clinical study.

Results: Correspondence with clinical study data is reasonable, especially considering that the model was not fitted in any way. Stenosis severity was confirmed to be an influential parameter. However, also cardiac period and graft diameter were observed to be important, particularly for mean flow rate and pulsatility index.

Conclusion: Metrics quantifying the flow waveform's diastolic dominance show the highest sensitivity to graft stenosis, and seem to be least affected by autoregulation. Among these, the novel diastolic resistance index shows the strongest sensitivity to stenosis severity.

Significance: The approach used in this study is expected to benefit the development of improved patency metrics, by allowing medical engineers to include sensitivity and uncertainty in assessing, in-silico, the potential of novel metrics, thus enabling them to provide better guidance in the design of clinical studies.

Purpose: Advancements in minimally invasive technologies to decrease postoperative morbidity and recovery times represent a large opportunity for mitral valve repair operations. However, current technologies are unable to replicate gold standard surgical neochord implantation.

Methods: We developed a novel neochordal repair device, Minimally Invasive Ventricular Anchoring Neochordoplasty (MIVAN), which operates via transcatheter, trans-septal anchoring to the posterior ventricular wall. We evaluated MIVAN in an ex vivo heart simulator and compared it with surgical neochordal repair and MitraClip using a prolapse model.

Results: Upon MIVAN repair of the model (n = 5), regurgitant fraction was reduced from 19.46 ± 1.77% to 7.30 ± 0.99% (p = 0.01). Surgical neochordal repair reduced regurgitant fraction to 5.65 ± 0.66%, but there was no significant difference between MIVAN and surgical repair (p = 0.22). Unpaired MitraClip repair had significantly higher regurgitant fraction of 11.9 ± 1.40%, compared with those of neochord (p < 0.01) and MIVAN (p = 0.03) repairs.

Conclusions: MIVAN represents a high-value opportunity for minimally invasive mitral valve repair. The benefits of the percutaneous, trans-septal approach for implantation on the posterior ventricular wall necessitate the expanded exploration of this device as a treatment alternative.