Computational modeling of low-density lipoprotein accumulation at the carotid artery bifurcation after stenting

Restenosis typically occurs in regions of low and oscillating wall shear stress, which also favor the accumulation of atherogenic macromolecules such as low-density lipoprotein (LDL). This study aims to evaluate LDL transport and accumulation at the carotid artery bifurcation following carotid artery stenting (CAS) by means of computational simulation. The computational model consists of coupled blood flow and LDL transport, with the latter being modeled as a dilute substance dissolved in the blood and transported by the flow through a convection-diffusion transport equation. The endothelial layer was assumed to be permeable to LDL, and the hydraulic conductivity of LDL was shear-dependent. Anatomically realistic geometric models of the carotid bifurcation were built based on pre- and post-stent computed tomography (CT) scans. The influence of stent design was investigated by virtually deploying two different types of stents (open- and closed-cell stents) into the same carotid bifurcation model. Predicted LDL concentrations were compared between the post-stent carotid models and the relatively normal contralateral model reconstructed from patient-specific CT images. Our results show elevated LDL concentration in the distal section of the stent in all post-stent models, where LDL concentration is 20 times higher than that in the contralateral carotid. Compared with the open-cell stents, the closed-cell stents have larger areas exposed to high LDL concentration, suggesting an increased risk of stent restenosis. This computational approach is readily applicable to multiple patient studies and, once fully validated against follow-up data, it can help elucidate the role of stent strut design in the development of in-stent restenosis after CAS

Vergleich der antimikrobiellen in vitro Wirksamkeit von Povidon-Iod und anderen kommerziell erhältlichen Antiseptika gegen klinisch relevante Pathogene

Aims: Antiseptics, such as povidone-iodine (PVP-I), play an important role in infection control across a wide range of clinical settings. This study aimed to evaluate the comparative in vitro efficacy and rate of onset of action of a range of formulations of PVP-I and other commonly used antiseptics.Methods: The antimicrobial efficacy of a range of antiseptics and antimicrobial agents used for skin, wound, vagina and oral antisepsis was evaluated according to the EU Standards DIN EN1276 and EN14476. The panel of organisms tested included bacterial and fungal pathogens and two enteroviruses (Coxsackievirus A16 [CA16] and Enterovirus 71 [EV71]). Results: All PVP-I products tested were highly efficacious in vitro (>99.99% kill rate) against a range of clinically relevant bacterial and fungal pathogens with rapid onset of action (30-60 seconds), at both high and low concentrations. By comparison, the efficacy of other antiseptics tested was generally reduced upon dilution. PVP-I products used in wound and oral care were found to be more effective in vitro against CA16 and EV71, and had a faster onset of action than most other agents tested.Conclusion: This study provides valuable insights into the in vitro efficacy of a range of commonly used antiseptics and may help inform the selection of appropriate antiseptics by healthcare professionals.Zielsetzung: Antiseptika wie Povidon-Iod (PVP-I) spielen eine wichtige Rolle in der Infektionskontrolle in einem breiten klinischen Anwendungsbereich. In der Studie sollte die in vitro -Wirksamkeit einer Reihe von Formulierungen auf Basis von PVP-I mit anderen häufig verwendeten Antiseptika verglichen werden.Methode: Gemäß DIN EN1276 und EN14476 wurde die antimikrobielle Wirksamkeit einer Reihe von Antiseptika und antimikrobiellen Wirkstoffen, die in Präparaten zur Anwendung auf Haut, Wunden, sowie zur Intim- und Mundpflege eingesetzt werden, geprüft. Das Panel der Prüforganismen umfasste bakterielle und pilzliche Erreger sowie zwei Enteroviren (Coxsackievirus A16 [CA16] und Enterovirus 71 [EV71]). Ergebnisse: Alle getesteten PVP-I-Produkte waren in vitro hochwirksam (>99,99% Abtötungsrate) gegen eine Reihe klinisch relevanter bakterieller und pilzlicher Erreger mit schnellem Wirkungseintritt (30-60 s) sowohl bei hohen als auch bei niedrigen Konzentrationen. Im Vergleich dazu war die Wirksamkeit anderer getesteter Antiseptika bei Verdünnung im Allgemeinen geringer. Zur Wund- und Mundhöhlenantiseptik eingesetzte PVP-I-Produkte erwiesen sich in vitro als wirksamer gegen CA16 und EV71 und hatten einen schnelleren Wirkungseintritt als die meisten anderen getesteten Mittel.Diskussion: Durch die Kenntnis der In-vitro -Wirksamkeit einer Reihe häufig verwendeter Antiseptika wird die Auswahl geeigneter Antiseptika durch medizinisches Fachpersonal erleichtert

A computational study of the effect of stent design on local hemodynamic factors at the carotid artery bifurcation

Background: Previous clinical studies have shown that the incidence of restenosis after carotid and coronary stenting varies with stent design and deployment configuration. This study aims to determine how stent design may affect in-stent hemodynamics in stented carotid arteries by means of Computational Fluid Dynamics (CFD). Methods: A robust computational method was developed to integrate detailed stent strut geometry in a patient-specific carotid artery reconstructed from medical images. Three stent designs, including two closed-cell stents and one open-cell stent, were reproduced and incorporated into the reconstructed post-stent carotid bifurcation. CFD simulations were performed under patient-specific flow conditions. Local hemodynamic parameters were evaluated and compared in terms of Wall Shear Stress (WSS), Oscillatory Shear Index (OSI) and Relative Residence Time (RRT). Results: All simulated stent designs induced some degree of flow disruption as manifested through flow separation and recirculation zones downstream of stent struts and quantified by WSS-related indices. Compared to the simulated open-cell stent, closed-cell stents created slightly larger areas of low WSS, elevated OSI and high RRT, due to a greater number of stent struts protruding into the lumen. Conclusion: Detailed stent design and patient-specific geometric features of the stented vessel have a strong influence on the evaluated hemodynamic parameters. Our limited computational results suggest that closed-cell stents may pose a higher risk for in-stent restenosis (ISR) than open-cell stent design. Further large-scale prospective studies are warranted to elucidate the role of stent design in the development of ISR after CAS

Disturbed flow in a stenosed carotid artery bifurcation: Comparison of RANS-based transitional model and LES with experimental measurements

Blood flow in the carotid arteries is usually laminar, but can undergo laminar-turbulent transition in the presence of a high-grade stenosis. In this study, pulsatile flow in a patient-based stenosed carotid artery bifurcation was examined using both large eddy simulation (LES) with dynamic Smagorinsky eddy viscosity model, and a Reynolds-averaged Navier-Stokes (RANS) method with a transitional version of the shear stress transport (SST-Tran) model. In addition, an experimental phantom was built for the same bifurcation geometry and velocity measurements were made using particle image velocimetry (PIV). Comparisons with PIV measurements of axial velocity profiles demonstrated that both SST-Tran and LES predicted the experimental results fairly well, with LES being slightly superior. Furthermore, LES predicted cycle-to-cycle variations in the region where transition to turbulence occurred, indicating the unsteady nature of turbulence transition. On the other hand, the SST-Tran model was able to capture important flow features observed in the PIV experiment, demonstrating its potential as a cost-effective alternative to LES for haemodynamic analyses of highly disturbed flow in diseased arteries