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1
Tafuna'i, Nicole Denney. "Arterial Blood Flow at Rest and During Exercise with Blood Flow Restriction". BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/9003.
Testo completoAbstract (sommario):
PURPOSE: This study comparted arterial occlusion pressure (AOP) of the superficial femoral artery (SFA) between the dominant and nondominant legs and the relationship between blood flow and occlusion pressure at rest and during muscle contractions in males and females. METHODS: The AOP of the SFA was measured using Doppler ultrasound in the dominant and nondominant legs of 35 (16 males, 19 females) apparently healthy, normotensive young adults. Blood flow in the SFA was measured in the resting state (REST) and during plantar flexion exercise (EXC) at occlusion pressures ranging from 0% to 100% of AOP. ANOVA was used to compare AOP between the dominant and nondominant legs and between males and females. Regression analysis was used to evaluate the influence of relevant variables on AOP. A mixed model was used to evaluate the relationship between blood flow and occlusion pressure at REST and during EXC. RESULTS: There was a significant difference in the AOP between the dominant and nondominant legs in males (230 ± 41 vs 209 ± 37 mmHg) and females (191 ± 27 vs 178 ± 21 mmHg), respectively. There was also a significant sex difference in the AOP in the dominant (230 ± 41 vs 191 ± 27 mmHg; p = 0.002) and nondominant (209 ± 37 vs 178 ± 21 mmHg; p = 0.004) legs, respectively. Regression analysis revealed that after accounting for leg circumference, age, sex, blood pressure, and skinfold thickness were not independent predictors of AOP. At REST and during EXC, there was a linear relationship between relative blood flow and occlusion pressure. CONCLUSIONS: Differences in leg circumference contribute to a portion of the differences in AOP between the dominant and nondominant legs and between sexes. The linear relationship between relative blood flow and occlusion pressure suggests that occlusion pressures during blood flow restriction exercise should be chosen carefully. A large variance in blood flow measurements at different occlusion pressures suggests the need for evaluating the reliability of blood flow measurements and standardization of methods.
2
Lutjemeier, Barbara June. "Control of muscle blood flow during dynamic exercise : muscle contraction / blood flow interactions". Diss., Manhattan, Kan. : Kansas State University, 2006. http://hdl.handle.net/2097/244.
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3
Nakashima, Tsutomu. "Autoregulation of Cochlear Blood Flow". 名古屋大学医学部, 1999. http://hdl.handle.net/2237/6202.
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4
Qamar, M. I. "Studies on intestinal blood flow". Thesis, University of Bristol, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372045.
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5
Aird, Graham Robert. "Blood flow in arterial branches". Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/10887.
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6
Dahnoun, Naim. "Continuous monitoring of blood flow". Thesis, University of Leicester, 1990. http://hdl.handle.net/2381/34319.
Testo completoAbstract (sommario):
An extensive review of the literature revealed that there are still significant weakness in the available technology for blood flow measurement. This dissertation describes two techniques for blood velocity measurement. The first is an invasive method which uses multimodal optical fibres for light transmission to and from a sensing tip, which attenuates the light depending upon the blood velocity. The design and construction of this flowmeter is presented and bench results shown. The modulated light is transmitted to the detection and processing circuit and provision is made for the transducer to be insensitive to pressure fluctuations and ambient light. The second technique, which is noninvasive, uses a continuous wave Doppler ultrasonic technique; the instrument designed is a portable directional Doppler velocimeter with purpose-built probes intended for monitoring blood flow in femorodistal bypass grafts in ambulatory patients. This portable unit differs from conventional Doppler units in many respect which are described. This unit has been developed in order to understand the behaviour of blood flow in grafts while the patients are persuing everyday tasks. A postoperative study of successful in situ vein grafts from 8 patients has been undertaken to determine the feasibility of the technique. This pilot study shows that posture can have an effect on blood flow in grafts, and also shows that it is possible to monitor blood velocity with Doppler techniques for a long period of time, without intervention of an operator.
7
Gammack, D. "Blood flow in twisted arteries". Thesis, University of Surrey, 1998. http://epubs.surrey.ac.uk/844008/.
Testo completoAbstract (sommario):
The motivation for this research into flow in pipes with non-uniform geometry comes from physiological flows. It is now widely believed that haemodynamics plays an important role in the initiation and development of atherosclerosis. Experiments have shown that the preferred sites for atherogenesis are regions of low wall shear stress. The build-up of atherosclerotic plaques in the coronary arteries can lead to arterial blockage and coronary failure. Previous studies have examined uniformly curved pipes and, more recently, uniformly curved and twisted pipes. However, it is well known that the arterial system displays non-uniform, time-dependent geometry. The main objective of this thesis is to describe flow in various pipes with weakly non-uniform curvature and torsion, with a view to understanding the resulting wall shear stress distribution and velocity profiles. The work herein models the flow of an incompressible Newtonian fluid through a pipe whose curvature and torsion vary along the pipe. The governing equations are first derived, then solved for both steady and oscillatory pressure gradients. The solution of these equations involves asymptotic and numerical techniques. The effects due to the non-uniform geometry and possible applications to physiology are discussed. Finally, the effects of torsion upon fluid motion are studied from the Lagrangian viewpoint, using numerical particle tracking.
8
deVries, Tiffany Dawn. "Neural Activation in Blood-Flow-Restricted Versus Non-Blood-Flow-Restricted Exercise: An fMRI Study". BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5878.
Testo completoAbstract (sommario):
Functional magnetic resonance imaging (fMRI) can be used to track neural activation in the brain during functional activities. The purpose of this study was to investigate brain neural responses to blood flow restricted (BFR) versus control handgrip exercise. Using a randomized crossover design, 25 subjects (12 males, 13 females) completed handgrip exercises during two conditions: BFR vs. control. To familiarize participants with the exercise conditions, one week prior to MRI scanning participants completed each exercise condition once on separate days, with 72 hours between days. The following week fMRI scans were performed at the same time of day, separated by 72 hours. The exercise protocol consisted of five 30-second sets of squeezing a nonmetallic handgrip exerciser (a reported 13.6 kg resistance), doing as many repetitions as possible, with 20-second rest intervals between sets. We saw a significant main effect of exercise condition (BFR versus control) between premotor dorsal (PMd)(F = 5.71, p = 0.022), premotor ventral (PMv)(F = 8.21, p = 0.007), and right ventral striatum (VS_R)(F = 7.36, p = 0.01). When considering anatomical regions of interest, we did not find significant differences between exercise conditions in bilateral S1 (p > 0.82), primary motor cortex (M1)(p > 0.33), supplementary motor area (SMA)(p > 0.66), cerebellum (CB)(p > 0.70), insular cortex (INS)(p > 0.45), anterior cingulate cortex (ACC)(p > 0.24), or thalamus (TH)(p > 0.66). Bilateral ACC (ACC_B), right middle frontal gyrus (MFG_R), and the right primary sensory cortex (S1_R) showed significant linear trends (p = 0.001) over the five exercise sets. Finally, the S1_R, left primary sensory cortex (S1_L), and the right anterior cingulate cortex (ACC_R) showed a main effect of set (p < 0.02). These data demonstrate that acute training with BFR during handgrip exercise results in different neural activation patterns in select areas of the brain, compared to a control. These results show that while completing less work with BFR exercise, subjects can achieve a similar amount of brain neural activation as with a higher-volume exercise. Brain neural activation is important to overall patient health and these findings may be important for prescribing training with BFR in clinical and applied research settings.
9
Tosenberger, Alen. "Blood flow modelling and applications to blood coagulation and atherosclerosis". Doctoral thesis, Institut Camille Jordan, CNRS UMR 5208, Université Claude Bernard Lyon 1, Université Claude Bernard Lyon 1, France, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/244806.
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10
Willie, Christopher Kenneth. "Cerebral blood flow in man : regulation by arterial blood gases". Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/47074.
Testo completoAbstract (sommario):
Due to the high metabolic rate of brain tissue and nominal substrate storage, brain perfusion must be precisely regulated to ensure continuous delivery of oxygen and substrates. Cerebral blood flow (CBF) is principally regulated by tissue metabolism, perfusion pressure, autonomic nervous activity, and the partial pressures of arterial oxygen (PaO₂)and carbon dioxide (PaCO₂) – an integrative process thus involving the marked influence of pulmonary gas exchange and cardiovascular function, in addition to intracranial mediators of cerebrovascular resistance. This thesis explicates the roles of PaO₂ and PaCO₂ in human regulation of regional CBF. In study 1, to elucidate their discrete roles, PaO₂ and PaCO₂ were independently manipulated at sea level through the widest range tolerated in humans. Flow reactivity to hypocapnia (low PaCO₂) and hypoxia (low PaO₂) was greater in the vertebral (VA) than internal carotid (ICA) artery, whereas similar reactivity was observed during hypercapnia (high PaCO₂) and hyperoxia (high PaO2₂. Cerebral oxygen delivery was well protected except in cases of extreme hypocapnia. The ventilatory response to hypoxia mitigates falling PaO₂ and reduces PaCO₂, particularly during initial exposure to high altitude. Study 2 assessed regional CBF during ascent to 5050m and every 12 hours during the first 3 days of acclimatization. Although total CBF increased by ~50% and was modestly related to reductions in oxygen saturation of hemoglobin, no regional CBF differences were observed. To extend these findings, Study 3 aimed to determine if cerebrovascular responses to changes in PaO₂ and PaCO₂ differed at 5050m compared to sea level. Despite respiratory alkalosis and partial metabolic compensation at 5050m restoration of PaO₂ to sea level values decreased CBF, and CBF sensitivity to acutely altered PaCO₂ remained similar to sea level. To elucidate the interactive effect on CBF of profound hypoxemia and hypercapnia, study 4 examined the temporal changes in elite breath-hold divers during maximum apneas. Despite 40-50% reductions in arterial oxygen content, CBF elevations were regionally similar (up to +100%) thereby facilitating maintenance of brain oxygen delivery throughout apnea. Although the regulation of CBF is multifaceted, the cerebrovasculature prioritizes oxygen delivery and adjusts to chronic changes in arterial blood gases.
11
Reasor, Daniel Archer. "Numerical simulation of cellular blood flow". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42760.
Testo completoAbstract (sommario):
In order to simulate cellular blood, a coarse-grained spectrin-link (SL) red blood cell (RBC) membrane model is coupled with a lattice-Boltzmann (LB) based suspension solver. The LB method resolves the hydrodynamics governed by the Navier--Stokes equations while the SL method accurately models the deformation of RBCs under numerous configurations. This method has been parallelized using Message Passing Interface (MPI) protocols for the simulation of dense suspensions of RBCs characteristic of whole blood on world-class computing resources.
Simulations were performed to study rheological effects in unbounded shear using the Lees-Edwards boundary condition with good agreement with rotational viscometer results from literature. The particle-phase normal-stress tensor was analyzed and demonstrated a change in sign of the particle-phase pressure from low to high shear rates due to RBCs transitioning from a compressive state to a tensile state in the flow direction. Non-Newtonian effects such as viscosity shear thinning were observed for shear rates ranging from 14-440 inverse seconds as well as the strong dependence on hematocrit at low shear rates. An increase in membrane bending energy was shown to be an important factor for determining the average orientation of RBCs, which ultimately affects the suspension viscosity. The shear stress on platelets was observed to be higher than the average shear stress in blood, which emphasizes the importance of modeling platelets as finite particles.
Hagen-Poiseuille flow simulations were performed in rigid vessels for investigating the change in cell-depleted layer thickness with shear rate, the Fåhraeus-Linqvist effect, and the process of platelet margination. The process of platelet margination was shown to be sensitive to platelet shape. Specifically, it is shown that lower aspect ratio particles migrate more rapidly than thin disks. Margination rate is shown to increase with hematocrit, due to the larger number of RBC-platelet interactions, and with the increase in suspending fluid viscosity.
12
Järhult, Susann J. "Hyperemic Brachial Artery Blood Flow Velocity". Doctoral thesis, Uppsala universitet, Medicin, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132918.
Testo completoAbstract (sommario):
This thesis aims to evaluate the blood flow velocity in the Brachial artery during reactive hyperemia. Primarily to appraise the information it might contain regarding cardiovascular function and cardiovascular risk. Ultrasonographic doppler measurements of the Brachial artery were made on the 1016 men and women aged 70 included in the prospective investigation of the vasculature in Uppsala seniors (PIVUS) study. Analysis of the blood flow velocity in the forearm was made in comparison to established methods of estimating endothelial function, clinical markers of cardiovascular risk, the Framingham risk score and global atherosclerosis determined by whole body magnetic resonance angiography. Systolic blood flow velocity was positively related to cardiovascular risk whereas the diastolic velocity was inversely correlated. However, the systolic to diastolic blood flow velocity (SDFV) ratio was more closely associated with cardiovascular risk than its components apart. Ultrasonographic markers of Carotid atherosclerosis were related to the SDFV ratio. Concentric left ventricular remodeling and left ventricular mass index were also associated with the SDFV ratio, but not to its numerator or denominator separately. A similar pattern was found when assessing SDFV ratio in relation to global atherosclerosis, as well as to established markers of arterial compliance and vasodilation. In conclusion, during reactive hyperemia of the Brachial artery, the systolic to diastolic blood flow velocity ratio appears to contain information of additional value than its components separately, independently of established cardiovascular risk factors. Possibly, the SDFV ratio could offer a promising means to estimate cardiovascular risk in aging populations.PIVUS
13
Scott, Adrian Roy. "Peripheral blood flow and diabetes mellitus". Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303002.
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14
Nasimi, Seerous Ghulam Abbas Ali. "Analysis of skin blood flow signals". Thesis, University of Bradford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305700.
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15
Koirala, Nischal. "Access Blood Flow Measurement Using Angiography". Cleveland State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=csu153796812445051.
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Jones, Elizabeth Anne Vincent Fraser Scott E. Fraser Scott E. "Blood flow and the mammalian embryo /". Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-05262005-102319.
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17
Lorenzetti, Fulvio. "Blood flow in free microvascular flaps". Helsinki : University of Helsinki, 2001. http://ethesis.helsinki.fi/julkaisut/laa/kliin/vk/lorenzetti/.
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18
Cardinal, Trevor Ryan. "Blood Flow Control During Ischemic Revascularization". Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195388.
Testo completoAbstract (sommario):
Control of blood flow to skeletal muscle is essential to maintain the overall homeostasis of an organism. The primary route that skeletal muscle uses to accommodate an increased metabolic demand associated with physical activity is to increase its blood flow through functional hyperemia. The importance of functional hyperemia in ensuring proper skeletal muscle function spurred 130 years of investigation into the mechanism(s) regulating its occurrence.Despite not identifying the essential factor(s) for controlling skeletal muscle blood flow, the last century of investigation has uncovered much about the process; including the observation that skeletal muscle functional hyperemia is impaired with ischemic disease. In patients, this can result in immobility, chronic ulcerations, gangrene, and at worst, amputation. To develop efficacious therapies, we as scientists must develop a better understanding of the molecular mechanisms underlying impaired vascular function during ischemia.The goal of this work was to lay the foundation for investigations examining the role of specific gene products involved in modulating blood flow control during ischemic revascularization by assessing vascular function in the mouse following an ischemic event. Unique among research animals, the mouse is routinely accessible for targeted genetic disruption, which allows investigators to assess the requirement of specific gene-products in a physiological process. Unfortunately, to date, no publication that I am aware of describes blood flow measurement to contracting mouse skeletal muscle following an ischemic/revascularization event. Therefore, the primary objective of this work was to assess vascular function in genetically unaltered animals.I found that unlike other species thus far examined, vascular dysfunction is not an obligatory response to hindlimb ischemic revascularization in the mouse. Ex vivo vasodilation responses to acetylcholine were statistically significantly impaired in the muscular branch artery 14 days following an ischemic event. However, using a newly developed fluorescent microsphere-based approach for determining skeletal muscle blood flow, I found that functional hyperemia was similar for the gracilis posterior muscle between non-ischemic and day-14 ischemic animals. In light of the primary literature, these findings suggest that vascular growth, and not ischemia per se is the primary regulator of vascular function during health and disease.
19
Arciero, Julia. "Theoretical Models of Blood Flow Regulation". Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/195903.
Testo completoAbstract (sommario):
In normal tissues, blood supply is closely matched to tissue demand for wide ranges of oxygen demand and arterial pressure. This suggests that multiple mechanisms regulate blood flow. Theoretical models can be used to analyze these interacting mechanisms. One proposed mechanism for metabolic flow regulation involves the saturation-dependent release of ATP by red blood cells, which triggers an upstream conducted response signal and arteriolar vasodilation. To analyze this mechanism, oxygen and ATP levels are calculated along a flow pathway of seven representative segments, including two vasoactive arteriolar segments. The conducted response signal is dependent on ATP concentration. Arteriolar tone depends on the conducted response signal, local wall shear stress and wall tension. Arteriolar diameters are calculated based on vascular smooth muscle mechanics. The model can account for increases in perfusion consistent with experimental findings at low and moderate oxygen consumption rates despite the opposing effects of the myogenic and shear-dependent responses. Autoregulation, the maintenance of nearly constant blood flow as arterial pressure varies, is assessed in the presence or absence of the myogenic, shear-dependent and/or metabolic responses. The model results indicate that the combined effects of myogenic and metabolic regulation overcome the vasodilatory effect of the shear-dependent response to generate autoregulatory behavior. Capillary recruitment has been shown to increase the capacity for oxygen delivery during exercise. In the model, capillary density is assumed to depend on small arteriole diameter. The model predicts a significant increase in the range over which perfusion can be regulated when recruitment is included. Oscillations in diameter and tone are predicted under certain conditions, suggesting a novel mechanism for vasomotion. The conditions that give rise to oscillations are analyzed. It is shown that the appearance of oscillations depends in a complex way on a number of system parameters. In summary, the theoretical model provides a quantitative assessment of the myogenic, shear-dependent and metabolic responses that affect blood flow regulation and identifies a role for capillary recruitment and vasomotion in the control of blood flow.
20
Kuzborska, Zyta. "Research of blood flow and stresses in the pathological blood vessels". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20120131_135725-24904.
Testo completoAbstract (sommario):
Physical load, age and gender influence to blood pressure and maximal stresses in the pathological blood vessel palaces was studies in this work. The main research subject – pathological blood vessel and its blood flow processes that depend on physical load, pathology degree and type, age, gender and blood vessels stress characteristics. The main aim of this work – to examine blood flow characteristics, local blood pressure, stress distribution in the pathological blood vessels dependent physical load assessing blood vessels mechanical properties variations due to age, gender, blood vessel pathology type; to make simplified human efficiency evaluation methodology. The paper analyse a few main tasks:
to explore physical load, blood vessels pathology degree, age and gender influence to blood pressure and tensions increase in the pathological blood vessels locations; experimentally determine blood flow rates changes in pathological blood vessels assessing; additionally investigate blood pressure and heart rate characteristics variations during set physical load and human working age range.
This paper consists of introduction, four chapters, summary, literature and authors publications theses lists and two annexes.
Introductory chapter discusses the test problem, work topicality, research subject, also formulates work subject and tasks, and describes research methodology, work scientific novelty, practical value of the work results, defended propositions. In the introduction end... [to full text]Disertacijoje nagrinėjama fizinio krūvio, amžiaus bei lyties įtaka kraujo spaudimui ir didžiausiems įtempiams pažeistoje kraujagyslės vietoje. Pagrindinis tyrimo objektas – ligos pažeista kraujagyslė ir joje vykstantys kraujo tėkmės procesai, priklausantys nuo fizinio krūvio dydžio, pažeidimo laipsnio ir rūšies, amžiaus, lyties, bei šių veiksnių įtaka didžiausiems įtempiams ir spaudimui pažeistose vietose. Pagrindinis disertacijos tikslas – ištirti kraujo tėkmės charakteristikas, lokalinį kraujo spaudimą, įtempių pasiskirstymą pažeistose kraujagyslėse priklausomai nuo fizinio krūvio, įvertinant kraujagyslių mechaninių savybių pokytį dėl amžiaus, lyties, kraujagyslės pažeidimo rūšies, ir sudaryti supaprastintą darbingumo verti-nimo metodiką. Darbe sprendžiami keli uždaviniai: ištirti fizinės apkrovos dydžio, kraujagyslių pažeidimų laipsnio, amžiaus ir lyties įtaką kraujo spaudimui ir įtempių padidėjimui pažeistose kraujagyslių vietose; ekspe-rimentiniu būdu nustatyti kraujo tėkmės rodiklių pokyčius pažeistose kraujagyslėse; ištirti kraujo spaudimo ir širdies susitraukimų dažnio charakteristikų pokyčius nustatytame fizinio krūvio ir žmogaus darbingo amžiaus intervale. Disertaciją sudaro įvadas, keturi skyriai, rezultatų apibendrinimas, naudotos literatūros ir autorės publikacijų disertacijos tema sąrašai ir du priedai. Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų... [toliau žr. visą tekstą]
21
Picot, Paul A. "Blood flow visualization and flow rate estimation with colour Doppler ultrasound". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ32324.pdf.
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22
Petersson, Sven. "Fast and Accurate 4D Flow MRI for Cardiovascular Blood Flow Assessment". Doctoral thesis, Linköpings universitet, Avdelningen för kardiovaskulär medicin, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-100146.
Testo completoAbstract (sommario):
The study of blood flow is essential in understanding the physiology and pathophysiology of the cardiovascular system. Small disturbances of the blood flow may over time evolve and contribute to cardiovascular pathology. While the blood flow in a healthy human appears to be predominately laminar, turbulent or transitional blood flow is thought to be involved in the pathogenesis of several cardiovascular diseases. Wall shear stress is the frictional force of blood on the vessel wall and has been linked to the pathogenesis of atherosclerosis and aneurysms. Despite the importance of hemodynamic factors, cardiovascular diagnostics largely relies on the indirect estimation of function based on morphological data. Time-resolved three-dimensional (3D) phase-contrast magnetic resonance imaging (MRI), often referred to as 4D flow MRI, is a versatile and non-invasive tool for cardiovascular blood flow assessment. The use of 4D flow MRI permits estimation of flow volumes, pressure losses, wall shear stress, turbulence intensity and many other unique hemodynamic parameters. However, 4D flow MRI suffers from long scan times, sometimes over 40 minutes. Furthermore, the accuracy of the many different 4D flow MRI-based applications and estimates have not been thoroughly examined. In this thesis, the accuracy of 4D flow MRI-based turbulence intensity mapping and wall shear stress estimation was investigated by using numerical simulations of MRI flow measurements. While the results from the turbulence intensity mapping agreed well with reference values from computational fluid dynamics data, the accuracy of the MRI-based wall shear stress estimates was found to be very sensitive to different parameters, especially to spatial resolution, and wall shear stress values over 5 N/m2 were not well resolved. To reduce the scan time, a 4D flow MRI sequence using spiral k-space trajectories was implemented and validated in-vivo and in-vitro. The scan time of 4D flow MRI was reduced by more than two-fold compared to a conventional Cartesian acquisition already accelerated using SENSE factor 2, and the data quality was maintained. For a 4D flow scan of the human heart, the use of spiral k-space trajectories resulted in a scan time of around 13 min, compared to 30 min for the Cartesian acquisition. By combining parallel imaging and spiral trajectories, the total scan time of a 4D flow measurement of the entire heart may be further reduced. This scan time reduction may also be traded for higher spatial resolution. Numerical simulation of 4D flow MRI may act as an important tool for future optimization and validation of the spiral 4D flow sequence. The scan-time reductions offered by the spiral k-space trajectories can help to cut costs, save time, reduce discomfort for the patient as well as to decrease the risk for motion artifacts. These benefits may facilitate an expanded clinical and investigative use of 4D flow MRI, including larger patient research studies.
23
Rahimian, Abtin. "Parallel algorithms for direct blood flow simulations". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43611.
Testo completoAbstract (sommario):
Fluid mechanics of blood can be well approximated by a mixture model of a Newtonian fluid and deformable particles representing the red blood cells. Experimental and theoretical evidence suggests that the deformation and rheology of red blood cells is similar to that of phospholipid vesicles. Vesicles and red blood cells are both area preserving closed membranes that resist bending. Beyond red blood cells, vesicles can be used to investigate the behavior of cell membranes, intracellular organelles, and viral particles. Given the importance of vesicle flows, in this thesis we focus in efficient numerical methods for such problems: we present computationally scalable algorithms for the simulation of dilute suspension of deformable vesicles in two and three dimensions. Our method is based on the boundary integral formulation of Stokes flow. We present new schemes for simulating the three-dimensional hydrodynamic interactions of large number of vesicles with viscosity contrast. The algorithms incorporate a stable time-stepping scheme, high-order spatiotemporal discretizations, spectral preconditioners, and a reparametrization scheme capable of resolving extreme mesh distortions in dynamic simulations. The associated linear systems are solved in optimal time using spectral preconditioners. The highlights of our numerical scheme are that (i) the physics of vesicles is faithfully represented by using nonlinear solid mechanics to capture the deformations of each cell, (ii) the long-range, N-body, hydrodynamic interactions between vesicles are accurately resolved using the fast multipole method (FMM), and (iii) our time stepping scheme is unconditionally stable for the flow of single and multiple vesicles with viscosity contrast and its computational cost-per-simulation-unit-time is comparable to or less than that of an explicit scheme. We report scaling of our algorithms to simulations with millions of vesicles on thousands of computational cores.
24
Framle, Peter Thomas James. "Blood flow and transport in artificial devices". Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399319.
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25
John, Gareth W. "Measurement of venous blood flow using photoplethysmography". Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/54076/.
Testo completoAbstract (sommario):
This simple, non-invasive test will reduce the patient numbers requiring the more time-consuming ultrasound examination, by screening out a high proportion of individuals who definitely do not have lower limb DVT. However, further signal processing methods should be investigated to improve the specificity of the test.
26
Poulin, Marc J. "Aspects of cerebral blood flow in humans". Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:a2af655f-9198-4cd0-a126-57c070f6399d.
Testo completoAbstract (sommario):
The technique of transcranial Doppler ultrasound (TCD) was used to assess cerebral blood flow (CBF) in humans. Studies were performed at rest and during dynamic submaximal exercise. In the resting experiments, TCD was combined with the technique of dynamic end-tidal forcing to study the dynamics of the CBF response to step changes in end-tidal (i.e. arterial) PC02 and PO2 In the resting and exercise experiments, the degree of consistency was examined between three indices of CBF that can be extracted from the TCD spectrum. Finally, the ventilatory and the CBF responses to acute isocapnic hypoxia were examined to try to quantify the possible reduction in ventilation that could be attributed to changes in CBF with hypoxia. In the studies performed at rest, during either hypoxia and/or hypercapnia (Chapter 2), the three indices of CBF extracted from the TCD spectrum were all consistent. However, during submaximal exercise (Chapter 5), the indices were less consistent and results suggest that the increase in CBF with exercise that has been reported with TCD needs to be treated with caution. The dynamic studies of the CBF response to step changes in end-tidal PC02 and PO2 in humans revealed that the CBF response to hypercapnia (Chapter 3) is characterised by a significant asymmetry, with a slower on-transient than off-transient, and also by a degree of undershoot following the relief of hypercapnia. The CBF response to hypocapnia (Chapter 4) is also characterised by a significant asymmetry, with a faster on-transient than off-transient. Furthermore, there is a slow progressive adaptation throughout the hypocapnic period. These studies show that the CBF responses to hypercapnia and hypocapnia are much faster than previously been thought. Finally, the work described in Chapter 6 attempts to quantify the possible reduction in ventilation that could be attributed to changes in CBF with hypoxia to determine whether it could be of sufficient magnitude to underlie hypoxic ventilatory decline (HVD). The results suggest that, in awake humans, changes in CBF during acute isocapnic hypoxia are quantitatively insufficient to underlie HVD.
27
Diwei, He M. Res. "Full field laser doppler blood flow sensor". Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523084.
Testo completo
28
Kongsavatsak, Chayut. "Full field laser doppler blood flow camera". Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489689.
Testo completoAbstract (sommario):
Laser Doppler Blood Flowmetry is a non-invasive technique that has been I developed and used for measuring microvascular blood flow in tissue. The technique utilises the backscattering of the laser light from moving red blood cells and static tissue in order to extract information such as the concentration and flow. This thesis describes the early stages of the development of an integrated optical sensor array to perform full field laser Doppler blood flow imaging. This technique will eliminate the need for mechanical scanning and the data bottleneck that exists between the photodiode array and processing unit, so allowing the direct measurement ofblood flow maps to be obtained in real time. A single channel laser Doppler blood flowmetry device has been implemented using a photodetector linked to a field programmable gate array. Filters (low pass, band pass and frequency weighted) have been developed for processing the Doppler signals to obtain flow and concentration measurements. The responses of these filters are demonstrated using measurements from modulated light signals, a rotating diffusing disc and in vivo measurements of blood flow. Several types of a linear array system and current to voltage converter are considered for the first fabrication run of the project based on the cost of fabrication and performance of the system such as operating frequency, gain, bandwidth and signal to noise ratio. A 16x1 linear array of photodiodes is developed and integrated on the same chip with the laser Doppler processing design, successfully implemented in the single channel laser Doppler system, using the standard 0.35Jlm CMOS technology. The characterisation of each individual part of the design was carried out and compared with the Cadence simulation results. The performance of the system on a single pixel is also evaluated using a modulated laser as a light source. The knowledge gained from the characterisation and the overall performance of the linear array system is then used to develop a full field laser Doppler blood flow camera.
29
Hazel, A. L. "Modelling of blood flow near arterial walls". Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603908.
Testo completoAbstract (sommario):
In this thesis, theoretical models of fluid flows close to arterial walls are studied. There are two main areas of study: (i) Flow near an oscillating stagnation point. The existence of a stagnation point which oscillates in position as well as in strength has been observed at certain sites prone to occlusive arterial disease. The two oscillations can interact non-linearly, altering the mean shear stress distribution on the wall. The problem is studied analytically and numerically in two and three dimensions, where in the three-dimensional case the basic stagnation-point flow is axisymmetric. In the physiologically relevant regime, it is found that the positional oscillations break the symmetry of the system, shifting the point of lowest mean wall shear stress away from the centre of these oscillations. The mass transport properties of such a flow are also studied by calculating particle trajectories and mass fluxes. (ii) Flow over an isolated obstacle on a plane wall. The vascular endothelium is a monolayer of cells lining the arterial walls. The endothelial cells convert mechanical forces into biological responses and a dysfunction of this natural process is one of the many proposed mechanisms for the initiation of atherosclerosis. The endothelium is a non-uniform surface with crests at the cellular nuclei and troughs at junctions between cells. A model for a single endothelial nucleus raised above the cellular monolayer is considered here. The time- and length-scales are such that the local fluid behaviour is dominated by viscous forces and the steady Stokes equations are applicable. These equations are solved numerically by a boundary element collocation method and the total force on a variety of nuclear shapes is calculated. Further away from the nucleus, but still on a cellular length-scale, weak inertia effects are introduced. Fourier transform methods are then used to obtain a closed form solution for the pressures and stresses on the wall, which are investigated by asymptotic methods.
30
陳君漢 e Kwan-hon Chan. "Intracranial blood flow velocity following head injury". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1991. http://hub.hku.hk/bib/B31979567.
Testo completo
31
Al-Saad, Mohammed. "Blood flow simulation using smooth particle hydrodynamics". Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/105588/.
Testo completoAbstract (sommario):
Blood flow rheology is a complex phenomenon, and the study of blood flow in the human body system under normal and pathological conditions are considered to be of great importance in biomedical engineering. Consequently, it is important to identify the key parameters that influence the flow behaviour of blood. The characterisation of blood flow will also enable us to understand the flow parameters associated with physiological conditions such as atherosclerosis. Thrombosis plays a crucial role in stopping bleeding when a blood vessel is injured. Developing tools that can successfully study the influences of hemodynamics on thrombus formation in arteries and vessels are considered to be essential. This thesis describes the steps taken to develop computational tools that focus on using the meshless particle-based Lagrangian numerical technique, which is named the smoothed particle hydrodynamic (SPH) method, to study the flow behaviour of blood and to explore flow condition that induces the formation of thrombus in blood vessels. A weakly-compressible SPH method is used here to simulate blood flow inside vessels. The basic governing equations solved in the SPH are the mass and momentum conservation equations. Due its simplicity and effectiveness, the SPH method is employed here to simulate the process of thrombogenesis under the influence of various blood flow parameters. In the present SPH simulation, blood is modelled by particles that have the characteristics of plasma and platelets. To simulate a 3-dimensional coagulation of platelets which form a thrombus, the adhesion and aggregation process of platelets are modelled by an effective inter-particle force model. With these models, platelet motion in the flowing blood and platelet adhesion and aggregation are effectively coupled with viscous blood flow. In this study, the adhesion and aggregation of blood particles are performed inside vessels with various geometries and with different flow velocity scenarios. The capabilities of this strategy were evaluated by comparing the simulation results with existing numerical and experimental results. All of these cases realistically model the formation of thrombus including thrombus collapse and partial separation. This thesis is considered to be the first work that is dedicated to the SPH simulation of thrombus formation inside blood vessels with various geometries and under different flow conditions.
32
Mazzeo, M. D. "Lattice-Boltzmann simulations of cerebral blood flow". Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/19357/.
Testo completoAbstract (sommario):
Computational haemodynamics play a central role in the understanding of blood behaviour in the cerebral vasculature, increasing our knowledge in the onset of vascular diseases and their progression, improving diagnosis and ultimately providing better patient prognosis. Computer simulations hold the potential of accurately characterising motion of blood and its interaction with the vessel wall, providing the capability to assess surgical treatments with no danger to the patient. These aspects considerably contribute to better understand of blood circulation processes as well as to augment pre-treatment planning. Existing software environments for treatment planning consist of several stages, each requiring significant user interaction and processing time, significantly limiting their use in clinical scenarios. The aim of this PhD is to provide clinicians and researchers with a tool to aid in the understanding of human cerebral haemodynamics. This tool employs a high performance fluid solver based on the lattice-Boltzmann method (coined HemeLB), high performance distributed computing and grid computing, and various advanced software applications useful to efficiently set up and run patient-specific simulations. A graphical tool is used to segment the vasculature from patient-specific CT or MR data and configure boundary conditions with ease, creating models of the vasculature in real time. Blood flow visualisation is done in real time using in situ rendering techniques implemented within the parallel fluid solver and aided by steering capabilities; these programming strategies allows the clinician to interactively display the simulation results on a local workstation. A separate software application is used to numerically compare simulation results carried out at different spatial resolutions, providing a strategy to approach numerical validation. This developed software and supporting computational infrastructure was used to study various patient-specific intracranial aneurysms with the collaborating interventionalists at the National Hospital for Neurology and Neuroscience (London), using three-dimensional rotational angiography data to define the patient-specific vasculature. Blood flow motion was depicted in detail by the visualisation capabilities, clearly showing vortex fluid ow features and stress distribution at the inner surface of the aneurysms and their surrounding vasculature. These investigations permitted the clinicians to rapidly assess the risk associated with the growth and rupture of each aneurysm. The ultimate goal of this work is to aid clinical practice with an efficient easy-to-use toolkit for real-time decision support.
33
Myers, Lance Jonathan. "Mathematical modeling of foetal arterial blood flow". Doctoral thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/5143.
Testo completoAbstract (sommario):
Bibliography: leaves 187-211.The aim of this thesis was to develop an accurate and comprehensive computer model of the foetal circulatory system and to use this model to investigate influences of various haemodynamic viriables on common Doppler blood flow velocity waveform indices. The foetal model consists of an number of vascular compartments, cascaded together using electrical transmission line analogies.
34
Thomas, Stephen. "Antithrombotic agents under flow conditions". Thesis, Open University, 2003. http://oro.open.ac.uk/54153/.
Testo completoAbstract (sommario):
Haemostasis is the result of a fine balance of interactions between the endothelium, plasma proteins and blood cells under a wide range of flow rates. To mimic these conditions in vitro, a parallel plate flow chamber with human umbilical vein endothelial cells (HUVEC) or extracellular matrix (ECM) has been developed. A method to investigate thrombin generation (TG) in platelet rich defibrinated plasma was validated and used to investigate inhibition by two distinct classes of antithrombotic agents: anti-platelet antibodies and anticoagulants, including unfractionated heparin (UFH), low molecular weight heparin (LMWH) and hirudin. Increasing flow rates increased TG, which was higher in the presence of ECM than in the presence of HUVEC. All anti thrombotic agents investigated were less effective in the presence of ECM. The monoclonal anti-platelet glycoprotein (GP) lIb/IlIa antibody, RFGP56, partially inhibited TG under static or arterial flow conditions and was less effective under venous flow conditions. The monoclonal anti-platelet GP Iba antibody, RFGP37, did not inhibit TG under flow or static conditions. A combination of the two antibodies showed no further activity than RFGP56 alone. UFH, which has equal anti-factor Xa and anti-thrombin activity, was able to inhibit TG under static and flow conditions. On an anti-Xa unit basis, comparatively more LMWH (with a 10: 1 ratio of anti-factor Xa to anti-thrombin activity) was required to inhibit TG under static and venous conditions, but under arterial conditions LMWH was as effective as UFH. Hirudin, a thrombin specific inhibitor, was totally effective under static conditions, but was only able to inhibit up to 40 % ofTG under flow. This study shows that some anti-platelet agents can inhibit coagulation and this may contribute to their antithrombotic efficacy under certain flow conditions. Although both the anti-factor Xa and anti-thrombin activities of anticoagulants are effective, anti-factor Xa activity may play a more important inhibitory role under flow conditions.
35
Jayasinghe, Dulip. "The effect of blood pressure on the cerebral blood flow of preterm infants". Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490972.
Testo completoAbstract (sommario):
During the early postnatal period, some preterm infants experience periods of hypoxia, hypotension or both. Hypotension is associated with significant cerebral lesions and contributes to morbidity and mortality. The aetiology of the lesions is thought to be secondary to a loss of Cerebral Blood Flow (CBF) autoregulation, resulting in a pressure-passive CBF. Treatment of hypotension may require the use of inotropic agents that may also affect CBF. CBF can be measured by a number of techniques; one quantitative method is the intravenous 133Xe technique. To investigate the effects of blood pressure on the CBF of preterm infants, CBF was measured before and after treatment of hypotension. Infants received, in a stepwise manor, volume replacement, a dopamine. infusion of 5 JJ9/kg/min then randomisation between 10 JJ9/kg/min of dopamine (Group 1), or the addition of dobutamine infusion at 10 JJg/kg/min (Group 2). Analysis was performed in two stages; the infants were grouped according to blood pressure during acquisition of serial CBF estimates and analysed for the presence of autoregulation; secondly, the effect of inotropes on CBF was modelled. Sixty-one CBF recordings were obtained from 16 infants. Five infants were normotensive during CBF estimation, 11 were hypotensive at least once. CBF-MABP reactivity (95% CI) of the normotensive group was 1.9% (-0.8% to 4.7%) I mmHg llMABP; hypotensive group 1.9% (0.8% to 3.0). The PaCOz-CBF reactivity of the normotensive infants was 11.1% (6.8% to 15.5%) I KPa llPaCOz, that of the hypotensive infants was 4.1% (-5.0% to 14.1%). Twelve infants received at least 5 JJ9/kg/min of dopamine, 5 were SUbsequently randomised to Group1, 5 randomised to Group2. When the effects of MABP, PaC02 , postnatal age, dose of dopamine and dobutamine were modelled on CBF, MABP (2.1% (95% CI1.13.3%)/ mmHg L\MABP; p=0.0003) and postnatal age (1.1% (95% CI 0.12.1 %)/hour L\postnatal age; p=0.03) were found to be significant predictors of change in CBF. The 95% CI of MABP-CBF reactivity of the normotensive infants encompassed 0, interpreted as intact autoregulation, the lower CI of the hypotensive group did not, which was interpreted as absent autoregulation. Inotropes were not observed to affect CBF directly but could through increase in MABP via pressure-passive CBF.
36
Appaji, Abhisara Apoorva. "Estimating Cerebral Blood Flow from a Flow from a Rotatinal Angiographic System". Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504287.
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Born, Silvia. "Illustrative Flow Visualization of 4D PC-MRI Blood Flow and CFD Data". Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-154354.
Testo completoAbstract (sommario):
Das zentrale Thema dieser Dissertation ist die Anwendung illustrativer Methoden auf zwei bisher ungelöste Probleme der Strömungsvisualisierung. Das Ziel der Strömungsvisualisierung ist die Bereitstellung von Software, die Experten beim Auswerten ihrer Strömungsdaten und damit beim Erkenntnisgewinn unterstützt. Bei der illustrativen Visualisierung handelt es sich um einen Zweig der Visualisierung, der sich an der künstlerischen Arbeit von Illustratoren orientiert. Letztere sind darauf spezialisiert komplizierte Zusammenhänge verständlich und ansprechend zu vermitteln. Die angewendeten Techniken werden in der illustrativen Visualisierung auf reale Daten übertragen, um die Effektivität der Darstellung zu erhöhen. Das erste Problem, das im Rahmen dieser Dissertation bearbeitet wurde, ist die eingeschränkte Verständlichkeit von komplexen Stromflächen. Selbstverdeckungen oder Aufrollungen behindern die Form- und Strömungswahrnehmung und machen diese Flächen gerade in interessanten Strömungssituationen wenig nützlich. Auf Basis von handgezeichneten Strömungsdarstellungen haben wir ein Flächenrendering entwickelt, das Silhouetten, nicht-photorealistische Beleuchtung und illustrative Stromlinien verwendet. Interaktive Flächenschnitte erlauben die Exploration der Flächen und der Strömungen, die sie repräsentieren. Angewendet auf verschiedene Stromflächen ließ sich zeigen, dass die Methoden die Verständlichkeit erhöhen, v.a. in Bereichen komplexer Strömung mit Aufwicklungen oder Singularitäten. Das zweite Problem ist die Strömungsanalyse des Blutes aus 4D PC-MRI-Daten. An diese relativ neue Datenmodalität werden hohe Erwartungen für die Erforschung und Behandlung kardiovaskulärer Krankheiten geknüpft, da sie erstmals ein dreidimensionales, zeitlich aufgelöstes Abbild der Hämodynamik liefert. Bisher werden 4D PC-MRI-Daten meist mit Werkzeugen der klassischen Strömungsvisualisierung verarbeitet. Diese werden den besonderen Ansprüchen der medizinischen Anwender jedoch nicht gerecht, die in kurzer Zeit eine übersichtliche Darstellung der relevanten Strömungsaspekte erhalten möchten. Wir haben ein Werkzeug zur visuellen Analyse der Blutströmung entwickelt, welches eine einfache Detektion von markanten Strömungsmustern erlaubt, wie z.B. Jets, Wirbel oder Bereiche mit hoher Blutverweildauer. Die Grundidee ist hierbei aus vorberechneten Integrallinien mit Hilfe speziell definierter Linienprädikate die relevanten, d.h. am gefragten Strömungsmuster, beteiligten Linien ausgewählt werden. Um eine intuitive Darstellung der Resultate zu erreichen, haben wir uns von Blutflußillustrationen inspirieren lassen und präsentieren eine abstrakte Linienbündel- und Wirbeldarstellung. Die Linienprädikatmethode sowie die abstrakte Darstellung der Strömungsmuster wurden an 4D PC-MRI-Daten von gesunden und pathologischen Aorten- und Herzdaten erfolgreich getestet. Auch die Evaluierung durch Experten zeigt die Nützlichkeit der Methode und ihr Potential für den Einsatz in der Forschung und der KlinikThis thesis’ central theme is the use of illustrative methods to solve flow visualization problems. The goal of flow visualization is to provide users with software tools supporting them analyzing and extracting knowledge from their fluid dynamics data. This fluid dynamics data is produced in large amounts by simulations or measurements to answer diverse questions in application fields like engineering or medicine. This thesis deals with two unsolved problems in flow visualization and tackles them with methods of illustrative visualization. The latter is a subbranch of visualization whose methods are inspired by the art work of professional illustrators. They are specialized in the comprehensible and esthetic representation of complex knowledge. With illustrative visualization, their techniques are applied to real data to enhance their representation. The first problem dealt with in this thesis is the limited shape and flow perception of complex stream surfaces. Self-occlusion and wrap-ups hinder their effective use in the most interesting flow situations. On the basis of hand-drawn flow illustrations, a surface rendering method was designed that uses silhouettes, non-photorealistic shading, and illustrative surface stream lines. Additionally, geometrical and flow-based surface cuts allow the user an interactive exploration of the surface and the flow it represents. By applying this illustrative technique to various stream surfaces and collecting expert feedback, we could show that the comprehensibility of the stream surfaces was enhanced – especially in complex areas with surface wrap-ups and singularities. The second problem tackled in this thesis is the analysis of blood flow from 4D PC-MRI data. From this rather young data modality, medical experts expect many advances in the research of cardiovascular diseases because it delivers a three-dimensional and time-resolved image of the hemodynamics. However, 4D PC-MRI data are mainly processed with standard flow visualizaton tools, which do not fulfill the requirements of medical users. They need a quick and easy-to-understand display of the relevant blood flow aspects. We developed a tool for the visual analysis of blood flow that allows a fast detection of distinctive flow patterns, such as high-velocity jets, vortices, or areas with high residence times. The basic idea is to precalculate integral lines and use specifically designed line predicates to select and display only lines involved in the pattern of interest. Traditional blood flow illustrations inspired us to an abstract and comprehensible depiction of the resulting line bundles and vortices. The line predicate method and the illustrative flow pattern representation were successfully tested with 4D PC-MRI data of healthy and pathological aortae and hearts. Also, the feedback of several medical experts confirmed the usefulness of our methods and their capabilities for a future application in the clinical research and routine
38
Ramström, Sofia. "The role of platelets in whole blood coagulation /". Linköping : Univ, 2003. http://www.bibl.liu.se/liupubl/disp/disp2003/med776s.pdf.
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39
Norris, David G. "NMR flow imaging". Thesis, University of Aberdeen, 1986. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU009818.
Testo completoAbstract (sommario):
The phase-encoded method of NMR flow imaging is examined in detail. The motion of isochromatic groups in the direction of suitably balanced magnetic field gradients will give a phase change in the NMR signal directly proportional to the velocity, acceleration, or higher derivative of position, dependent upon the form of the field gradient. If a simple bipolar pulse is used then the phase change, for isochromats moving with constant velocity, will be proportional to the velocity. If two such pulses are placed back to back then the phase change is proportional to the acceleration. The motion of isochromats in the magnetic field gradients used for imaging will also cause phase changes. These effects are considered, and simple methods of reducing them presented. Phase errors due to main field inhomogeneity are shown to be eliminated by a simple phase difference technique. In this two image data sets having different flow sensitivities are obtained, and the phase difference between them calculated. Velocity images were obtained using this technique, both by the manipulation of the frequency-encoding and selection gradients, and by the insertion of bipolar pulses in the imaging sequence. Acceleration images were also produced by adding double bipolar pulses to the imaging sequence. Both spin-echo and field-echo sequences were used. Field-echo sequences were shown to be superior for high velocities, particularly when the direction of flow is through the slice, otherwise spin-echo sequences were preferred. The Fourier imaging of velocity is also examined, and images presented. This technique is only considered to be useful for projective imaging, where it is shown to have an SNR advantage over established methods. Using two specially designed phantoms the accuracy of all these techniques is shown to be within 5%.
40
Thistlethwaite, John R. "The Role of Acidosis on Vascular Function during Dynamic Handgrip Exercise and Flow-mediated Dilation". Connect to full text in OhioLINK ETD Center, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1216833858.
Testo completoAbstract (sommario):
Dissertation (Ph.D.)--University of Toledo, 2008.Typescript. "Submitted as partial fulfillment of the requirements for The Doctor of Philosophy degree in Exercise Science." Bibliography: leaves 5-7, 24-34, 61-66, 88-92.
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Nishimura, Nozomi. "Microvascular lesions and blood flow in rodent cortex". Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3211912.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of California, San Diego, 2006.Title from first page of PDF file (viewed July 10, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
42
Von, Krüger Marco Antônio. "Doppler ultrasound tracking instrument for monitoring blood flow". Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/29367.
Testo completoAbstract (sommario):
There are situations, during surgery, in the immediate post-operative period, and in neonatal and adult intensive care units, where monitoring the blood supply to a certain organ or region of the body could be of great value. Doppler ultrasound has great potential for monitoring blood flow velocity because it is a reliable, noninvasive method and produces results in real time. In addition, the development of Doppler technology associated with the recent progress of electronics and computerization has widened the range of information that can be extracted from the Doppler signal. Despite its great potential, there are difficulties which prevent the establishment of blood flow monitoring as a valuable clinical tool. Amongst these difficulties the one which appears to be the most important is the problem of fixing the transducer to the patient in order to prevent misalignment between ultrasound beam and vessel caused by patient movement. A Doppler tracking instrument which is able to adjust its beam direction automatically to ensure correct alignment between the beam and vessel would be valuable in overcoming this difficulty. The work described in this thesis led to the design, construction, and testing of hardware and software for such an instrument, which consists of a feedback controlled phased array transceiver, driving a one dimension array continuous wave Doppler transducer. With its operation it was possible to demonstrate the principle of Doppler tracking, which can open a wide area of monitoring to clinical ultrasound. From the construction point of view, this equipment was useful in identifying some guide lines to be followed in order to turn it into a device which can be used as a clinical tool.
43
Moore, Jennifer Anne. "Computational blood flow modelling in realistic arterial geometries". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0008/NQ35257.pdf.
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Macgowan, Christopher K. "Fast measurements of blood flow using magnetic resonance". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ59009.pdf.
Testo completo
45
Newton, Bradley Scot. "Blood flow evaluation using an intracoronary doppler catheter". Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/16404.
Testo completo
46
Lieberman, Howard M. "Modulation of penile blood flow through vasoactive agents". Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=30846.
Testo completoAbstract (sommario):
The erectile mechanism is a sequential cascade of events, involving many chemical messengers, perhaps the most important one being nitric oxide (NO). NO is a putative neurotransmitter involved in the non-adrenergic non-cholinergic (NANC) system and is synthesized by the enzyme nitric oxide synthase (NOS). NOS has been localized in peripheral autonomic nerves innervating vascular and non-vascular smooth muscles in many organ systems.The introduction of intracavernous injection (ICI) of vasoactive agents in 1981 was an effective means to restore erectile function for men with erectile dysfunction (ED). Recent evidence supports the theory that increased blood flow can induce the release of NO from vascular endothelium, suggesting that ICI may have positive benefits for the host.
Our study looked at (1) a new delivery system for intracavernous injection and (2) the effect of modulation of penile flow on the regulation of NOS content and activity. A canine model assessed the effectiveness of a subcutaneous drug delivery as an alternate means to ICI. Additionally, a paraplegic rat model was developed to assess the effects of chronic ICI of papaverine on the expression of NOS in the penile tissue.
Our first objective, testing a new subcutaneous drug delivery system, yielded no data due to technical difficulties. The experiment involving the rat model, our results demonstrated that ICI of papaverine significantly increased the number of NOS fibers within the penile shaft, indicating that an increase in the flow of blood within the penis can alter levels of NOS within penile tissue. This result may in part explain the observation seen in patients, whereby after 1 year of ICI, spontaneous erections return and ICI therapy may be discontinued.
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Gates, Andrew R. C. "Blood flow studies using nuclear magnetic resonance imaging". Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260496.
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Ardilouze, Jean-Luc. "Regulation of adipose tissue blood flow in humans". Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409721.
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Vejlstrup, Niels Grove. "Liquid balance and blood flow in the lungs". Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386661.
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50
吳志萍 e Chi-ping Ng. "Cerebral blood flow monitoring of brain injured patients". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31214484.
Testo completo