1,720,982 research outputs found
The role of hemodynamics in arteriovenous fistula remodelling and failure. A CFD longitudinal study
No full textTransitional flow in AVF: is there a correlation between wall vibrations and stenosis development?
No full textHemodynamics in AVF over time: A protective role of vascular remodeling toward flow stabilization
Full text linkThe mechanisms underlying vascular stenosis formation in the arteriovenous fistula (AVF) for hemodialysis (HD) remain mostly unknown. Several computational fluid dynamics (CFD) studies have suggested a potential role for unsteady flow in inducing intimal hyperplasia and AVF stenosis, but the majority of these observations have been limited to a single time point after surgical creation. The aim of the present study was to investigate the relation between hemodynamic conditions and AVF vascular remodeling through a CFD longitudinal study. Non contrast-enhanced MR images and Doppler Ultrasound (US) examinations were acquired at 3 days, 40 days, 6 months, 1 year, and 1.5 years after surgery in a 72-year male referred for native radio-cephalic AVF. Three-dimensional AVF models were generated and high fidelity CFD simulations were performed using pimpleFoam, setting patient-specific boundary conditions derived from US. Morphological and hemodynamic changes over time were then analyzed. Analysis of vessel morphology and hemodynamics during follow-up showed that the AVF had a successful maturation process, characterized by a massive arterial and venous dilatation within the 6 months after surgery, a corresponding increase in blood flow volume and important flow instabilities. Between 6 months and 1 year, a stenosis developed in the juxta-anastomotic vein and caused AVF failure at 1.5 years. The development of stenosis was paralleled by the regularization of blood flow velocity pattern and consequent decrease in the near-wall disturbed flow metrics. These results suggest that development of intimal hyperplasia and vessel stenosis, triggered by unsteady flow, could be the result of vascular inward remodeling toward regularization of turbulent-like flow
A Design Method of Tele-Rehabilitation Platforms for Post-Stroke Patients Based on Consumer Technology
Full text linkBackground: Telerehabilitation represents a new cutting-edge method in the treatment of patients suffering from motor and cognitive disorders caused by stroke. Even if there exist dedicated devices able to track patients' movements to evaluate the performed rehabilitation exercises, they require specific settings necessary for a correct and simple use at the patient's home. If we consider the recent pandemic situation and the lockdown condition, which made difficult the access to these products, post stroke patients may be not able to perform home rehabilitation.
Objectives: the goal of this work is the design of a specific method to develop a tele-rehabilitation platform for post-stroke patients using consumer technologies without involving ad-hoc devices.
Method: Open-source tools have been investigated for speeding up the development starting with the medical knowledge.
Results: a group of four healthcare technologies engineering students with no specific skills about computer science has developed a platform in four months using the design method.
Conclusion: the presented method allowed the development of a clinical knowledge-based web platform for post-stroke patients totally based on consumer technology
Impact of Modeling Assumptions on Hemodynamic Stresses in Predicting Cerebral Aneurysm Rupture Status
No full textApproximately 3% of the population is estimated to have cerebral aneurysms, which are the leading cause of subarachnoid haemorrhage. Convincing evidences suggest that wall shear stresses (WSS) play a role in vessel remodeling and in the development of vascular diseases. SinceWSS cannot be directly measured, researchers have resorted to using medical images available in routine clinical practice to simulate computational fluid dynamics (CFD) and investigate patient-specific vascular conditions. They retrospectively analyse the correlation between WSS and disease outcomes to find potential clinical tools for future use. However, most of these models are based on assumptions that introduce variability and error. In this work we investigated the effects of a non-Newtonian viscosity model and inflow uncertainty on the prediction of commonly computed hemodynamic metrics. Our results show a substantial influence of the non-Newtonian model and blood flow rate on CFD outcomes, highlighting the need of incorporating non-Newtonian rheology and patient-specific blood flow measurements in CFD simulations
High-Frequency Vessel Wall Vibrations Associate With Stenosis Formation and Arteriovenous Fistula Failure
Full text linkToward a physiological model of vascular wall vibrations in the arteriovenous fistula
No full textThe mechanism behind hemodialysis arteriovenous fistula (AVF) failure remains poorly understood, despite previous efforts to correlate altered hemodynamics with vascular remodeling. We have recently demonstrated that transitional flow induces high-frequency vibrations in the AVF wall, albeit with a simplified model. This study addresses the key limitations of our original fluid–structure interaction (FSI) approach, aiming to evaluate the vibration response using a more realistic model. A 3D AVF geometry was generated from contrast-free MRI and high-fidelity FSI simulations were performed. Patient-specific inflow and pressure were incorporated, and a three-term Mooney–Rivlin model was fitted using experimental data. The viscoelastic effect of perivascular tissue was modeled with Robin boundary conditions. Prescribing pulsatile inflow and pressure resulted in a substantial increase in vein displacement (+400%) and strain (+317%), with a higher maximum spectral frequency becoming visible above -42 dB (from 200 to 500 Hz). Transitioning from Saint Venant–Kirchhoff to Mooney–Rivlin model led to displacement amplitudes exceeding 10 micrometers and had a substantial impact on strain (+116%). Robin boundary conditions significantly damped high-frequency displacement (-60%). Incorporating venous tissue properties increased vibrations by 91%, extending up to 700 Hz, with a maximum strain of 0.158. Notably, our results show localized, high levels of vibration at the inner curvature of the vein, a site known for experiencing pronounced remodeling. Our findings, consistent with experimental and clinical reports of bruits and thrills, underscore the significance of incorporating physiologically plausible modeling approaches to investigate the role of wall vibrations in AVF remodeling and failure
The Potential of Sound Analysis to Reveal Hemodynamic Conditions of Arteriovenous Fistulae for Hemodialysis
Full text linkPurpose: Arteriovenous fistula (AVF), the preferred vascular access for hemodialysis, is associated with high failure rate. The aim of this study was to investigate the potential of AVF sound auscultation in providing quantitative information on AVF hemodynamic conditions.
Methods: This single-center prospective study involved six patients with native radio-cephalic AVFs who underwent multiple follow-up visits. Doppler Ultrasound blood flow volume (BFV) assessment and electronic stethoscope-based sound recordings were performed during each visit, whereas MRIs were acquired 3 days, 3 weeks and 1 year after surgery. Computational fluid dynamic (CFD) simulations were performed on patient-specific MRI-derived geometrical models.
Results: Higher values of median peak amplitudes ratios (high-low peak ratio-HLPR) were found to be associated with complex blood flow and velocity streamlines recirculation at systolic peak, and corresponding extended regions of high oscillatory shear index (OSI). On the contrary, lower values of HLPR were associated with laminar flow pattern and low values of OSI. Significant differences were observed in HLPR between subgroups with extended or limited areas with OSI > 0.1 (0.67 vs 0.31, respectively). Significant relationships were found between AVF sound intensity and brachial BFV (slope = 0.103, p < 0.01) as well as between longitudinal changes in brachial BFV and HLPR (slope = − 0.001, p < 0.01).
Conclusion: Our results show that AVF sound can be exploited to extract fundamental information on AVF hemodynamic conditions, providing indication of the presence of complex hemodynamic and adequate BFV to perform hemodialysis. Sound analysis has therefore the potential to improve clinical AVF surveillance and to ameliorate outcom
Computational fluid dynamic simulations to assess hemodynamical significance of fibromuscular dysplasia–related renal artery stenosis: a feasibility study
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