27 research outputs found
Population‐specific modelling of between/within‐subject flow variability in the carotid arteries of the elderly
Get PDFComputational fluid dynamics models are increasingly proposed for assisting the diagnosis and management of vascular diseases. Ideally, patient‐specific flow measurements are used to impose flow boundary conditions. When patient‐specific flow measurements are unavailable, mean values of flow measurements across small cohorts are used as normative values. In reality, both the between‐subjects and within‐subject flow variabilities are large. Consequently, neither one‐shot flow measurements nor mean values across a cohort are truly indicative of the flow regime in a given person. We develop models for both the between‐subjects and within‐subject variability of internal carotid flow. A log‐linear mixed effects model is combined with a Gaussian process to model the between‐subjects flow variability, while a lumped parameter model of cerebral autoregulation is used to model the within‐subject flow variability in response to heart rate and blood pressure changes. The model parameters are identified from carotid ultrasound measurements in a cohort of 103 elderly volunteers. We use the models to study intracranial aneurysm flow in 54 subjects under rest and exercise and conclude that OSI, a common wall shear‐stress derived quantity in vascular CFD studies, may be too sensitive to flow fluctuations to be a reliable biomarker
Subject-specific multiporoelastic model for exploring the risk factors associated with the early stages of Alzheimer's disease
Get PDFThere is emerging evidence suggesting that Alzheimer’s disease is a vascular disorder, caused by impaired cerebral perfusion, which may be promoted by cardiovascular risk factors that are strongly influenced by lifestyle. In order to develop an understanding of the exact nature of such a hypothesis, a biomechanical understanding of the influence of lifestyle factors is pursued. An extended poroelastic model of perfused parenchymal tissue coupled with separate workflows concerning subject-specific meshes, permeability tensor maps and cerebral blood flow (CBF) variability is utilised. The subject-specific datasets used in the modelling of this paper were collected as part of prospective data collection. Two cases were simulated involving male, non-smokers (control and MCI case) during two states of activity (high and low). Results showed a marginally reduced clearance of CSF/ISF, elevated parenchymal tissue displacement and CSF/ISF accumulation and drainage in the MCI case. Peak perfusion remained at 8 mm/s between the two cases
Subject-specific multi-poroelastic model for exploring the risk factors associated with the early stages of Alzheimer's disease
Get PDFnone14siThere is emerging evidence suggesting that Alzheimer’s disease is a vascular disorder, caused by impaired cerebral perfusion, which may be promoted by cardiovascular risk factors that are strongly influenced by lifestyle. In order to develop an understanding of the exact nature of such a hypothesis, a biomechanical understanding of the influence of lifestyle factors is pursued. An extended poroelastic model of perfused parenchymal tissue coupled with separate workflows concerning subject-specific meshes, permeability tensor maps and cerebral blood flow variability is used. The subject-specific datasets used in the modelling of this paper were collected as part of prospective data collection. Two cases were simulated involving male, non-smokers (control and mild cognitive impairment (MCI) case) during two states of activity (high and low). Results showed a marginally reduced clearance of cerebrospinal fluid (CSF)/interstitial fluid (ISF), elevated parenchymal tissue displacement and CSF/ISF accumulation and drainage in the MCI case. The peak perfusion remained at 8 mm s-1 between the two cases.noneGuo L.; Vardakis J.C.; Lassila T.; Mitolo M.; Ravikumar N.; Chou D.; Lange M.; Sarrami-Foroushani A.; Tully B.J.; Taylor Z.A.; Varma S.; Venneri A.; Frangi A.F.; Ventikos Y.Guo L.; Vardakis J.C.; Lassila T.; Mitolo M.; Ravikumar N.; Chou D.; Lange M.; Sarrami-Foroushani A.; Tully B.J.; Taylor Z.A.; Varma S.; Venneri A.; Frangi A.F.; Ventikos Y
Hemodynamics of thrombus formation in intracranial aneurysms: an in-silico observational study
Get PDFHow prevalent is spontaneous thrombosis in a population containing all sizes of intracranial aneurysms? How can we calibrate computational models of thrombosis based on published data? How does spontaneous thrombosis differ in normo- and hypertensive subjects? We address the first question through a thorough analysis of published datasets that provide spontaneous thrombosis rates across different aneurysm characteristics. This analysis provides data for a subgroup of the general population of aneurysms, namely, those of large and giant size (>10 mm). Based on these observed spontaneous thrombosis rates, our computational modeling platform enables the first in silico observational study of spontaneous thrombosis prevalence across a broader set of aneurysm phenotypes. We generate 109 virtual patients and use a novel approach to calibrate two trigger thresholds: residence time and shear rate, thus addressing the second question. We then address the third question by utilizing this calibrated model to provide new insight into the effects of hypertension on spontaneous thrombosis. We demonstrate how a mechanistic thrombosis model calibrated on an intracranial aneurysm cohort can help estimate spontaneous thrombosis prevalence in a broader aneurysm population. This study is enabled through a fully automatic multi-scale modeling pipeline. We use the clinical spontaneous thrombosis data as an indirect population-level validation of a complex computational modeling framework. Furthermore, our framework allows exploration of the influence of hypertension in spontaneous thrombosis. This lays the foundation for in silico clinical trials of cerebrovascular devices in high-risk populations, e.g., assessing the performance of flow diverters in aneurysms for hypertensive patients
The association of health literacy with adherence in older 2 adults, and its role in interventions: a systematic meta-review
Get PDFBackground: Low health literacy is a common problem among older adults. It is often suggested to be associated with poor adherence. This suggested association implies a need for effective adherence interventions in low health literate people. However, previous reviews show mixed results on the association between low health literacy and poor adherence. A systematic meta-review of systematic reviews was conducted to study the association between health literacy and adherence in adults above the age of 50. Evidence for the effectiveness of adherence interventions among adults in this older age group with low health literacy was also explored. Methods: Eight electronic databases (MEDLINE, ERIC, EMBASE, PsycINFO, CINAHL, DARE, the Cochrane Library, and Web of Knowledge) were searched using a variety of keywords regarding health literacy and adherence. Additionally, references of identified articles were checked. Systematic reviews were included if they assessed the association between health literacy and adherence or evaluated the effectiveness of interventions to improve adherence in adults with low health literacy. The AMSTAR tool was used to assess the quality of the included reviews. The selection procedure, data-extraction, and quality assessment were performed by two independent reviewers. Seventeen reviews were selected for inclusion. Results: Reviews varied widely in quality. Both reviews of high and low quality found only weak or mixed associations between health literacy and adherence among older adults. Reviews report on seven studies that assess the effectiveness of adherence interventions among low health literate older adults. The results suggest that some adherence interventions are effective for this group. The interventions described in the reviews focused mainly on education and on lowering the health literacy demands of adherence instructions. No conclusions could be drawn about which type of intervention could be most beneficial for this population. Conclusions: Evidence on the association between health literacy and adherence in older adults is relatively weak. Adherence interventions are potentially effective for the vulnerable population of older adults with low levels of health literacy, but the evidence on this topic is limited. Further research is needed on the association between health literacy and general health behavior, and on the effectiveness of interventions
FREE VIBRATION ANALYSIS OF SANDWICH PLATES WITH THE MAGNETIC VISCOELASTIC FLUID CORE USING SPLINE FINITE STRIP METHOD
No full textSandwich plates containing magnetic fluids in the core are considered nowadays
as a smart structure. Due to the ability of rapid change in the viscosity of the fluid in the core, plate can be used to control the vibration of the structure and to deplete the energy. In the present study, free vibration behavior of a sandwich plate, which is made of composite glass-epoxy fiber face sheets and contains magnetic fluid in the core, is investigated. Based on the Hamilton's principle and considering independent bending degrees of freedom for upper and lower faces, free vibration governing equations of the plate are derived using the spline finite strip method. To validate the proposed method, the results are compared with those of other similar studies using different methods. Then, the effects of different parameters, e.g., diverse boundary conditions, which are rarely considered elsewhere, are evaluated based on the proposed formulation. Moreover, the frequency impacts as well as the modal loss factor, which are the two main parameters in the vibration analysis of these structures, are considered and the effect of different factors such as magnetic field intensity and fluid thickness in the core are investigated. The results indicate that the spline finite strip method has good accuracy in analyzing
sandwich plates containing a flexible core. Besides, the results show that
increasing the intensity of the magnetic field causes an increase in the
frequency and loss factor corresponding to each mode. Moreover, increasing the
thickness of the fluid leads to increase in the loss factor and decrease in the
frequency. The results indicate that despite the change in the strain energy of
the structure, due to changes in the fiber orientation of the composite layers,
the frequency of each mode does not change significantly. It was also found
that the clamped plate had the highest frequency and the simply supported
boundary condition had the lowest frequency
Bending analysis of functionally graded sandwich plates using the refined finite strip method
No full textA New Analytical Approach for Free Vibration, Buckling and Forced Vibration of Rectangular Nanoplates Based on Nonlocal Elasticity Theory
No full textNonlocal Galerkin Strip Transfer Function Method for Vibration of Double-Layered Graphene Mass Sensor
No full textWhat Do We Know About One-to-One Peer Support for Adults With a Burn Injury? A Scoping Review
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