Cardiovascular Engineering and Technology最新文献

Purpose: This study explores the use of heart rate variability (HRV) analysis, a noninvasive technique for assessing the autonomic nervous system, by applying nonlinear dynamics and chaos theory to detect chaotic behavior in RR intervals and assess cardiovascular health.

Methods: Employing the "System Analysis of Heart Rate Dynamics" (SADR) program, this research combines chaos analysis with the short-time Fourier transform to assess nonlinear dynamic parameters in HRV. It includes constructing phase portraits in Takens space and calculating measures of chaos to identify deterministic chaos indicators.

Results: The analysis identifies distinct chaos indicators in the cardiac rhythm of healthy volunteers compared to tachyarrhythmia patients, both before and after catheter treatment. Post-radiofrequency ablation (RFA) analysis shows promise as a predictive tool for arrhythmia recurrence.

Conclusions: The findings suggest that HRV analysis, through nonlinear dynamics, can be an effective noninvasive method for predicting arrhythmia recurrence following treatments like catheter ablation. This approach has the potential for early and precise detection of arrhythmia, pending further validation.

Introduction: Extracorporeal membrane oxygenation is a lifesaving treatment for patients with refractory acute respiratory, circulatory, or combined cardiopulmonary failure. The patient is cannulated with one or two cannulae for drainage and reinfusion of blood. Blood is drained from the patient, pumped through a membrane lung for oxygenation and returned to the patient. Treatment efficiency depends on correct cannula positioning and interactions between drainage and reinfusion cannula.

Methods: An experimental setup was built to study the isolated drainage performance of 24 Fr rigid models of a blunt and lighthouse tip cannula, both when centered and when tilted towards the vessel wall. Planar particle image velocimetry was used to investigate the flow field with water as the fluid medium.

Results: For similar flow configuration, higher shear stresses were recorded in the blunt tip rather than lighthouse tip cannula. Moreover, in the lighthouse tip cannula, side-holes furthest from the tip (proximal side-holes) had the highest drainage. Results did not change substantially when the cannula was tilted towards the vessel wall.

Conclusions: The effective drainage point of the lighthouse tip cannula was located near the proximal side-holes. Lower shear stresses were recorded in the lighthouse tip cannula when compared with the blunt tip cannula, for all considered flow rate ratios and cannula positions.

Purpose: Computational models of the cardiovascular system continue to increase in complexity. As more elements of the physiology are captured in multiscale models, there is a need to efficiently integrate subsystems. The objective of this study is to demonstrate the effectiveness of a coupling methodology, called functional mock-up interface (FMI), as applied to multiscale cardiovascular modeling.

Methods: The multiscale model is composed of two subsystems: a computational fluid dynamics (CFD) model coupled to a lumped parameter model (LPM). The LPM is packaged using the FMI standard and imported into the CFD subsystem using an FMI co-simulation architecture. The functionality of an FMI coupling was demonstrated in a univentricular parallel circulation by means of compatible tools, including ANSYS CFX and Python. Predicted pressures and flows were evaluated in comparison with clinical data and a previously developed computational model.

Results: The two models exchanged pressure and flow data between their boundaries at each timestep, demonstrating sufficient inter-subsystem communication. The models recreated pressures and flows from clinical measurements and a patient-specific model previously published.

Conclusion: FMI integrated with ANSYS CFX is an effective approach for interfacing cardiovascular multiscale models as demonstrated by the presented univentricular circulatory model. FMI offers a modular approach towards tool integration and is an advantageous strategy for modeling complex systems.

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.

Purpose: A triple lumen iteration of the novel photo-angioplasty drug eluting balloon catheter (DEBc) Lumi-Solve may be compromised by guidewire shadow (GWS)-mediated attenuation of balloon surface drug activation. The current study aimed to design and evaluate a novel triple lumen prototype, designated Lumi-Solve-T, to circumvent these issues.

Methods: Effects of guidewire shadowing (GWS) on vascular smooth muscle cell (VSMC) proliferation was evaluated using the MTT assay. In-silico modelling of GWS in the novel triple lumen design was conducted. Computer-aided design (CAD) and finite element analysis (FEA) contributed to development of a novel triple lumen catheter. 3D printing of rudimentary and refined prototypes of the catheter together with assembly of a novel fibre-optic (FO) complex and ex-vivo evaluation of the triple lumen device, Lumi-Solve T, was also performed.

Results: GW insertion in a parallel triple lumen FO: GW port orientation demonstrated significantly reduced inhibition of VSMC proliferation after 7 days confirming the need for an alternative triple lumen design. In-silico analysis identified a multi-fibre FO sleeve design supported uniform, radial and uninterrupted UV365nm light transmission to the angioplasty balloon surface. FEA confirmed a multi-fibre FO ribbon design afforded a practical method of FO sleeve generation and facilitated a novel hub configuration able to afford a FO ribbon to sleeve transition. 3D printed prototypes demonstrated the utility of the novel design.

Conclusions: A dedicated third port and lumen for the Lumi-Solve FO is required for optimal balloon surface photo-activation. A novel triple lumen design, Lumi-Solve-T, incorporating a ribbon to sleeve FO transition and novel hub design offers a realistic solution to current device limitations.

The flow convergence method includes calculation of the proximal isovelocity surface area (PISA) and is widely used to classify mitral regurgitation (MR) with echocardiography. It constitutes a primary decision factor for determination of treatment and should therefore be a robust quantification method. However, it is known for its tendency to underestimate MR and its dependence on user expertise. The present work systematically compares different pulsatile flow profiles arising from different regurgitation orifices using transesophageal echocardiographic (TEE) probe and particle image velocimetry (PIV) as a reference in an in-vitro environment. It is found that the inter-observer variability using echocardiography is small compared to the systematic underestimation of the regurgitation volume for large orifice areas (up to 52%) where a violation of the flow convergence method assumptions occurs. From a flow perspective, a starting vortex was found as a dominant flow pattern in the regurgant jet for all orifice shapes and sizes. A series of simplified computational fluid dynamics (CFD) simulations indicate that selecting a suboptimal aliasing velocity during echocardiography measurements might be a primary source of potential underestimation in MR characterization via the PISA-based method, reaching up to 40%. In this study, it has been noted in clinical observations that physicians often select an aliasing velocity higher than necessary for optimal estimation in diagnostic procedures.

Purpose: Pulmonary atresia with intact ventricular septum is a multifactorial disease requiring complex surgeries. The treatment route is determined based on the right ventricle (RV) size, tricuspid annulus size and coronary circulation dependency of RV. Since multiple parameters influence the post-operative success, a personalized decision-making based on computed hemodynamics is hypothesized to improve the treatment efficacy.

Methods: A lumped parameter cardiovascular model is developed to calculate the hemodynamics of virtual patients which are generated by statistical distribution of circulation parameters. Four cohorts each with 30 digital patients are grouped based on RV size. For each patient, biventricular and one-and-half ventricle (1.5 V) repair were applied in silico and assessed via pressure, flow and saturations computed for every organ bed.

Results: Biventricular and 1.5 V repair yield significant increase in the pulmonary flow and oxygen saturation for all patients compared to the pre-operative state (p-values < 0.001). Approximately 30% of generated patients failed to meet the sufficient saturation and flow following biventricular repair and were directed to 1.5 V repair. However, 14% of these 1.5 V repair patients failed post-operatively, requiring Fontan completion. Based on the pre-determined hemodynamics criteria, this study implies that patients having RV sizes larger than 22 ml/m² are likely to undergo successful biventricular repair.

Conclusion: Pending further clinical trials, computational pre-interventional planning has the potential to screen patients that would not optimally fit to the traditional pathway prior to in vivo execution by providing personalized hemodynamic outcome. Statistical approach allows in silico clinical trials, useful for diseases with low patient numbers.

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: Recent studies have identified an effect of glycosaminoglycans (GAG) on residual stresses in the aorta, underscoring the need to better understand their biomechanical roles.

Methods: Aortic ring models for each of the ascending, arch and descending thoracic regions of the porcine thoracic aorta were created in FEBioStudio, using a framework that incorporates the Donnan osmotic swelling in a porous solid matrix. The distribution of fixed charge densities (FCD) through the thickness of the tissue was prescribed as calculated from experimentally quantified sulfated GAG mural distributions. Material parameters for the solid matrix, modeled using a Holmes-Mow constitutive law, were optimized using data from biaxial tensile tests. In addition to modelling the solid matrix as one layer, two layers were considered to capture the differences between the intima-media and the adventitia, for which various stiffness ratios were explored.

Results: As the stiffness of the adventitia with respect to that of the media increased, the simulated opening angle increased. The opening angle also decreased from the ascending to the descending thoracic region in both one- and two-layered solid matrices models. The simulated results were compared against the experimental contribution of GAG to the opening angle, as previously quantified via enzymatic GAG-depletion. When using one layer for the solid matrix, the errors between the simulated opening angles and the experimental contribution of GAG to the opening angle were respectively 28%, 15% and 23% in the ascending, arch and descending thoracic regions. When using two layers for the solid matrix, the smallest errors in the ascending and arch regions were 21% and 5% when the intima-media was modelled as 10 times stiffer, and as twice stiffer than the adventitia, respectively, and 23% in the descending thoracic regions when the intima-media and adventitia shared similar mechanical properties.

Conclusions: Overall, this study demonstrates that GAG partially contribute to circumferential residual stress, and that GAG swelling is one of several regulators of the opening angle. The minor discrepancies between simulated and experimental opening angles imply that the contribution of GAG extends beyond mere swelling, aligning with previous experimental indications of their interaction with ECM fibers in determining the opening angle.

Purpose: Central venous catheters (CVCs) provide a direct route to the venous circulation but are prone to catheter-related thrombosis (CRT). A known CRT risk factor is a high catheter-to-vein ratio (CVR), or a large catheter diameter with respect to the indwelling vein size. In this study, the CVR's effect on CVC hemodynamics and its impact on CRT is investigated with in vitro and in silico experiments.

Methods: An in vitro flow loop is used to characterize the hemodynamics around CVCs using particle image velocimetry. In addition, CRT is investigated using an in vitro flow loop with human blood and clinical catheters. The wall shear rate of flow around the CVC is computed numerically. CVRs of 0.20, 0.33, and 0.49 and Reynolds numbers of 200, 800, and 1300 are evaluated. No flow is used through CVC lumens to model chronic indwelling catheters.

Results: Results show CVR ≥ 0.33 promotes platelet-rich clot growth at the device tip and at an increased rate compared to lower CVR cases. A high wall shear rate gradient on the CVC tip and an extended wake distal to the tip exists for higher CVR cases, promoting the aggregation of platelets and subsequent stagnation for clot formation. Further, the combination of the CVR and Reynolds number are crucial to CRT potential, not the CVR alone. Specifically, thrombosis risk is increased with low (stasis driven) and/or high (platelet activation driven) flow conditions, with the CVR and CVC's geometry playing an additional role in promoting fluid mechanic driven thrombus development. A high CVR (≥ 0.33) and high flow condition (≥ 1300) results in the highest risk for clot growth at the tip of the device; other locations of the device are at risk for thrombus development in lower flow conditions, regardless of the CVR. The importance of the device geometry and flow in promoting thrombus and fibrin sheath formation is also shown for the device investigated.

Conclusions: This work demonstrates that the CVR, flow, and device geometry affect CRT. For clinical cases with CVR ≥ 0.33 and/or Re ≥ 1300, the device tip may be monitored more consistently for clot formation. Thrombosis risks remain on the entire catheter, regardless of the flow condition, for a CVR = 0.49. Device placement should be chosen carefully with respect to the combination of the Reynolds number and CVR. Further study is needed on the effect of catheterization to confirm these findings.