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Hemodynamic Properties (hemodynamic + property)
Selected AbstractsStructural and biophysical simulation of angiogenesis and vascular remodeling ,DEVELOPMENTAL DYNAMICS, Issue 4 2001Ralf Gödde Abstract The purpose of this report is to introduce a new computer model for the simulation of microvascular growth and remodeling into arteries and veins that imitates angiogenesis and blood flow in real vascular plexuses. A C++ computer program was developed based on geometric and biophysical initial and boundary conditions. Geometry was defined on a two-dimensional isometric grid by using defined sources and drains and elementary bifurcations that were able to proliferate or to regress under the influence of random and deterministic processes. Biophysics was defined by pressure, flow, and velocity distributions in the network by using the nodal-admittance-matrix-method, and accounting for hemodynamic peculiarities like Fahraeus-Lindqvist effect and exchange with extravascular tissue. The proposed model is the first to simulate interdigitation between the terminal branches of arterial and venous trees. This was achieved by inclusion of vessel regression and anastomosis in the capillary plexus and by remodeling in dependence from hemodynamics. The choice of regulatory properties influences the resulting vascular patterns. The model predicts interdigitating arteriovenous patterning if shear stress-dependent but not pressure-dependent remodeling was applied. By approximating the variability of natural vascular patterns, we hope to better understand homogeneity of transport, spatial distribution of hemodynamic properties and biomass allocation to the vascular wall or blood during development, or during evolution of circulatory systems. © 2001 Wiley-Liss, Inc. [source] Comparative velocity investigations in cerebral arteries and aneurysms: 3D phase-contrast MR angiography, laser Doppler velocimetry and computational fluid dynamicsNMR IN BIOMEDICINE, Issue 8 2009Dorothea I. Hollnagel Abstract In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3,Tesla MR scanner, laser Doppler velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field. Copyright © 2009 John Wiley & Sons, Ltd. [source] Quantitative characterization of hemodynamic properties and vasculature dysfunction of high-grade gliomasNMR IN BIOMEDICINE, Issue 6 2007Vijaya Nagesh Abstract Aberrations in tumor and peritumoral vasculature may not be distinguishable by cerebral blood flow (CBF) or cerebral blood volume (CBV) alone. The relationships between CBF and CBV were examined to estimate vasculature-specific hemodynamic characteristics. Twenty glioma patients were studied with dynamic susceptibility T2*-weighted MRI [(dynamic contrast-enhanced magnetic resonance imaging (DSC-MRI)] before and during week 1 and 3 of radiotherapy (RT). CBF and CBV were calculated from DSC-MRI, and relationships between the two were evaluated: the physiological measure of mean transit time (MTT),=,CBV/CBF; empirical fitting using the power law CBV,=,constant,×,(CBF),. Three different tissue types were assessed: the Gd-enhancing tumor volume (GEV); non-enhanced abnormal tissue located beyond GEV but within the abnormal hyperintense region on FLAIR images (NEV); normal tissue in the hemisphere contralateral to the tumor (CNT). The effects of tissue types, CBV magnitudes (low, medium and high), before and during RT, on MTT and , were analyzed by analysis of variance (ANOVA). The MTT and , for the three tissue types were significantly different (p,<,0.009). MTT increased from CNT (1.60,s) to NEV (1.93,s) to GEV (2.28,s) (p,<,0.0005). , was significantly greater in GEV (1.079) and NEV (1.070) than in CNT (1.025). , increased with increasing CBV magnitude while MTT was independent of CBV magnitude. There was a significant decrease in MTT of NEV and GEV during week 3 of RT compared with pre-RT values for all CBV magnitudes. There was a significant increase in , during RT in the tumor and peritumor. Progressive abnormalities in vasculature and hemodynamic characteristics of the vascular bed were delineated, with significant disorder in the tumor but mild abnormality in peritumoral tissue. Copyright © 2007 John Wiley & Sons, Ltd. [source] Phenylhydrazine as a partial model for ,-thalassaemia red blood cell hemodynamic propertiesBRITISH JOURNAL OF HAEMATOLOGY, Issue 6 2008Yuval Ramot Summary ,-Thalassaemia is a congenital haemoglobinopathy, associated with red blood cells (RBC) anomalies, leading to impairment of their flow-affecting properties, namely, RBC deformability, self-aggregability, and adherence to endothelial cells (EC). Treatment of normal RBC with phenylhydrazine (PHZ) causes selective association of oxidized ,-globin chains with the membrane skeleton, leading to reduced RBC deformability, characteristic of ,-thalassaemia. PHZ has thus been used to mimic phenotypes of ,-thalassaemia RBC. The present study was undertaken to further elucidate the suitability of PHZ-treated RBC as a model for ,-thalassemic RBC, by comparing the aggregability and adhesiveness of PHZ-treated RBC to those of RBC from thalassaemia intermedia (TI) patients, using image analysis of RBC under flow. In addition, the externalization of phosphatidylserine (PS), a mediator of RBC/EC interaction, was determined. It was found that PHZ caused enhanced RBC adhesiveness to extracellular matrix, similar to TI-RBC. Furthermore, in both conditions, the enhanced adhesiveness was mediated by PS translocated to the RBC surface. In contrast, PHZ treatment completely abolished RBC aggregability, while TI-RBC aggregability was slightly elevated. It is proposed that PHZ-treated RBC resemble ,-thalassaemia RBC in their deformability and adhesiveness, but not in their aggregability, and thus can be used as a limited model for ,-thalassaemia RBC phenotypes. [source] | ||||||||||