In this thesis, a parallel solver was developed for the modelling of blood flow through a number of patient-specific geometries. A locally conservative Galerkin (LCG) spatial discretisation was applied along with an artificial compressibility and characteristic based split (CBS) scheme to solve the 3D incompressible Navier-Stokes equations. The Spalart-Allmaras one equation turbulence model was also optionally employed. The solver was constructed using FORTRAN and the Message Passing Interface (MPI). Parallel testing demonstrated linear or better than linear speedup on hybrid patient-specific meshes. These meshes were unstructured with structured boundary layers. From the parallel testing it is clear that the significance of inter-processor communication is negligible in a three dimensional case. Preliminary tests on a short patient-specific carotid geometry demonstrated the need for ten or more boundary layer meshes in order to sufficiently resolve the peak wall shear stress (WSS) along with the peak time-averaged WSS. A time sensitivity study was also undertaken along with the assessment of the order of the real time step term. Three backward difference formulae (BDF) were tested and no significant difference between them was detected. Significant speedup was possible as the order of time discretisation increased however, making the choice of BDF important in producing a timely solution. Followed by the preliminary investigation, four more carotid geometries were investigated in detail. A total of six haemodynamic wall parameters have been brought together to analyse the regions of possible atherogenesis within each carotid. The investigations revealed that geometry plays an overriding influence on the wall parameter distribution. Each carotid artery displayed high time-averaged WSS at the apex, although the value increased significantly with a proximal stenosis. Two out of four meshes contained a region of low time-averaged WSS distal to the flow divider and within the largest connecting artery (internal or external carotid artery), indicating a potential region of atherosclerosis plaque formation. The remaining two meshes already had a stenosis in the corresponding region. This is in excellent agreement with other established works. From the investigations, it is apparent that a classification system of stenosis severity may be possible with potential application as a clinical diagnosis aid. Finally, the flow within a thoracic aortic aneurysm was investigated in order to assess the influence of a proximal folded neck. The folded neck had a significant effect on the wall shear stress, increasing by up to 250% over an artificially smoothed neck. High wall shear stresses may be linked to aneurysm rupture. Being proximal to the aneurysm, this indicated that local geometry should be taken into account when assessing the rupture potential of an aneurysm.

Doctor of Philosophy / Department of Anatomy and Physiology / David C. Poole / The purpose of this dissertation is to expand our knowledge on the physiological effects of the ubiquitous signaling molecule nitric oxide (NO). Focus is given to the impacts of the nitrate (NO[subscript]3[superscript]-) nitrite (NO[subscript]2[superscript]-) NO pathway on skeletal muscle vascular and metabolic function during exercise. The NO[subscript]3[superscript]--NO[subscript]2[superscript]--NO pathway has garnered tremendous research interest due to its ability to upregulate NO bioavailability independently of NO synthase (NOS) function and thus impact the metabolic responses to exercise. Chapter 2 demonstrates that NO[subscript]3[superscript]- supplementation via beetroot juice (BR) augments the skeletal muscle vascular responses to exercise. Five days of BR supplementation resulted in a significantly higher skeletal muscle blood flow (BF) and vascular conductance (VC) during exercise when compared to control. The increases in BF and VC were preferentially directed to muscles and muscle portions comprised predominantly of fast twitch fibers. Furthermore, exercising blood [lactate] was reduced, suggesting improved metabolic control. In chapter 3, BR resulted in a slower fall in the microvascular PO[subscript]2 (PO[subscript]2[subscript]m[subscript]v, the soul driving force for blood myocyte O[subscript]2 flux) during the crucial rest-contraction transition thereby preserving the pressure head needed to move O[subscript]2 from the capillary into the myocyte. Chapter 4 examines the effects of BR on fast vs. slow twitch muscles in which BR raised the PO[subscript]2[subscript]m[subscript]v during the steady state of muscle contractions in fast but not slow twitch muscles, likely due to the lower PO[subscript]2[subscript]m[subscript]v at rest and throughout muscle contractions within these tissues. Chapter 5 investigates the effects of direct arterial NO[subscript]2[superscript]- infusion on skeletal muscle BF and VC during exercise in rats with NOS blockade via N[superscript]G-nitro-L arginine methyl ester. NO[subscript]2[superscript]- infusion restored MAP and VC to levels observed in healthy control animals (with intact NOS function) highlighting the potential for a NO[subscript]2[superscript]- based therapy to positively impact vascular function in those with compromised NOS function such that is evident in many prevalent diseases. These results provide crucial mechanistic insight into the improved exercise tolerance observed in humans following NO[subscript]3[superscript]- supplementation whilst also challenging our current understanding of NO’s role in physiology and pathophysiology.

Made available in DSpace on 2014-10-09T12:34:00Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:05Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:34:00Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:05Z (GMT). No. of bitstreams: 0 / O sinal de fluxo cutâneo obtido via fluxometria Laser Doppler (SFLD) tem flutuações de baixas frequências que estão relacionadas a mecanismos de controle do fluxo microvascular. Análises espectrais, via transformada de Fourier e transformada de wavelet, têm sido usadas para correlacionar as flutuações de SFLD com os seguintes mecanismos de controle de fluxo: metabólico, metabólico NO-dependente, neurogênico e miogênico, nos respectivos intervalos de frequência 0,005-0,0095 Hz, 0,0095-0,02 Hz, 0,02-0,05 Hz e 0,05-0,15 Hz. A potência do sinal, em cada intervalo de frequência, geralmente é usada como uma medida da atividade do mecanismo de controle microvascular relacionado. Uma vez que os métodos usados de análise são espectrais, as características das flutuações do SFLD, em cada intervalo de frequência, no domínio do tempo são desconhecidas. Como consequência, há ausência de critérios objetivos para medir adequadamente, em cada intervalo de frequência, os parâmetros hemodinâmicos relacionados. O objetivo deste trabalho foi caracterizar e quantificar flutuações temporais, espaciais e espaço-temporais do SFLD em cada faixa de frequência, usando um método no domínio do tempo. Os fluxos basais (320C) e termicamente estimulados à (420C) das regiões volares de antebraços de 20 voluntários saudáveis foram coletados em duas regiões próximas e analisados. As análises dos dados obtidos indicam que janelas temporais pequenas (1 minuto) são aceitáveis para a quantificação do fluxo médio, e que janelas temporais maiores são necessários para quantificar as flutuações de fluxo. A análise espaço-temporal revelou uma forte correlação entre sinais (em todas as bandas, exceto na banda B5) das duas regiões investigadas, durante longos intervalos de tempo, quando as duas regiões estudadas foram termicamente estimuladas, e menor variabilidade intragrupo quando comparada à obtida para os valores médios das flutuações, sugerindo que o intervalo de tempo de correlação é um parâmetro promissor para estudar mecanismos de controle do fluxo microvascular. / Tese (Doutoramento) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

The brain microcirculation plays a key role in cerebral physiology and neuronal activation. In the case of degenerative diseases such as Alzheimer’s, severe deterioration of the microvascular networks (e.g. vascular occlusions) limit blood flow, thus oxygen and nutrients supply, to the cortex, eventually resulting in neurons death. In addition to functional neuroimaging, modelling is a valuable tool to investigate the impact of structural variations of the microvasculature on blood flow and mass transfers. In the brain microcirculation, the capillary bed contains the smallest vessels (1-10 μm in diameter) and presents a mesh-like structure embedded in the cerebral tissue. This is the main place of molecular exchange between blood and neurons. The capillary bed is fed and drained by larger arteriolar and venular tree-like vessels (10-100 μm in diameter). For the last decades, standard network approaches have significantly advanced our understanding of blood flow, mass transport and regulation mechanisms in the human brain microcirculation. By averaging flow equations over the vascular cross-sections, such approaches yield a one-dimensional model that involves much fewer variables compared to a full three-dimensional resolution of the flow. However, because of the high density of capillaries, such approaches are still computationally limited to relatively small volumes (<100 mm3). This constraint prevents applications at clinically relevant scales, since standard imaging techniques only yield much larger volumes (∼100 cm3), with a resolution of 1-10 mm3. To get around this computational cost, we present a hybrid approach for blood flow modelling where the capillaries are replaced by a continuous medium. This substitution makes sense since the capillary bed is dense and space-filling over a cut-off length of ∼50 μm. In this continuum, blood flow is characterized by effective properties (e.g. permeability) at the scale of a much larger representative volume. Furthermore, the domain is discretized on a coarse grid using the finite volume method, inducing an important computational gain. The arteriolar and venular trees cannot be homogenized because of their quasi-fractal structure, thus the network approach is used to model blood flow in the larger vessels. The main difficulty of the hybrid approach is to develop a proper coupling model at the points where arteriolar or venular vessels are connected to the continuum. Indeed, high pressure gradients build up at capillary-scale in the vicinity of the coupling points, and must be properly described at the continuum-scale. Such multiscale coupling has never been discussed in the context of brain microcirculation. Taking inspiration from the Peaceman “well model” developed for petroleum engineering, our coupling model relies on to use analytical solutions of the pressure field in the neighbourhood of the coupling points. The resulting equations yield a single linear system to solve for both the network part and the continuum (strong coupling). The accuracy of the hybrid model is evaluated by comparison with a classical network approach, for both very simple synthetic architectures involving no more than two couplings, and more complex ones, with anatomical arteriolar and venular trees displaying a large number of couplings. We show that the present approach is very accurate, since relative pressure errors are lower than 6 %. This lays the goundwork for introducing additional levels of complexity in the future (e.g. non uniform hematocrit). In the perspective of large-scale simulations and extension to mass transport, the hybrid approach has been implemented in a C++ code designed for High Performance Computing. It has been fully parallelized using Message Passing Interface standards and specialized libraries (e.g. PETSc). Since the present work is part of a larger project involving several collaborators, special care has been taken in developing efficient coding strategies.

Diameters of microvessels undergo continuous structural adaptation in response to hemodynamic and metabolic stimuli. To ensure adequate flow distribution, metabolic responses are needed to increase diameters of vessels feeding poorly perfused regions. Possible modes of metabolic control include release of signaling substances from vessel walls, from the supplied tissue and from red blood cells (RBC). Here, a theoretical model was used to compare the abilities of these metabolic control modes to provide adequate tissue oxygenation, and to generate blood flow velocities in agreement with experimental observations. Structural adaptation of vessel diameters was simulated for an observed mesenteric network structure in the rat with 576 vessel segments. For each mode of metabolic control, resulting distributions of oxygen and deviations between simulated and experimentally observed flow velocities were analyzed. It was found that wall-derived and tissue-derived growth signals released in response to low oxygen levels could ensure adequate oxygen supply, but RBC-derived signals caused inefficient oxygenation. Closest agreement between predicted and observed flow velocities was obtained with wall-derived growth signals proportional to vessel length. Adaptation in response to oxygen-independent release of a metabolic signal substance from vessel walls or the supplied tissue was also shown to be effective for ensuring tissue oxygenation due to a dilution effect if growth signal substances are released into the blood. The present results suggest that metabolic signals responsible for structural adaptation of microvessel diameters are derived from vessel walls or from perivascular tissue.

The current thesis examined whether sex-differences in local and whole-body heat loss are evident after accounting for confounding differences in physical characteristics and rate of metabolic heat production. Three experimental studies were performed: the first examined whole-body heat loss in males and females matched for body mass and surface area during exercise at a fixed rate of metabolic heat production; the second examined local and whole-body heat loss responses between sexes during exercise at increasing requirements for heat loss; the third examined sex-differences in local sweating and cutaneous vasodilation to given doses of pharmacological agonists, as well as during passive heating. The first study demonstrates that females exhibit a lower whole-body sudomotor thermosensitivity (553 ± 77 vs. 795 ± 85 W•°C-1, p=0.05) during exercise performed at a fixed rate of metabolic heat production. The second study shows that whole-body sudomotor thermosensitivity is similar between sexes at a requirement for heat loss of 250 W•m-2 (496 ± 139 vs. 483 ± 185 W•m-2•°C-1, p=0.91) and 300 W•m-2 (283 ± 70 vs. 211 ± 66 W•m-2•°C-1, p=0.17), only becoming greater in males at a requirement for heat loss of 350 W•m-2 (197 ± 61 vs. 82 ± 27 W•m-2•°C-1, p=0.007). In the third study, a lower sweat rate to the highest concentration of acetylcholine (0.27 ± 0.08 vs. 0.48 ± 0.13 mg•min-1•cm-2, p=0.02) and methylcholine (0.41 ± 0.09 vs. 0.57 ± 0.11 mg•min-1•cm-2, p=0.04) employed was evidenced in females, with no differences in cholinergic sensitivity. Taken together, the results of the current thesis show that sex itself can modulate sudomotor activity, specifically the thermosensitivity of the response, during both exercise and passive heat stress. Furthermore, the results of the third study point towards a peripheral modulation of the sweat gland as a mechanism responsible for the lower sudomotor thermosensitivity in females.

An experimental animal model was developed to study and define the relationship between the blood flow and the marrow cavity pressure of bone. The study was carried out in 24 rabbits and 32 dogs under nembutol anesthesia. A multichannel physiograph was used to record simultaneously the systemic blood pressure, bone blood flow, marrow cavity pressure of bone and time sequence. The systemic blood pressure was measured by cannulating a brachial or carotid artery. The bone blood flow was measured by cannulating the nutrient vein and/or the nutrient artery. The marrow cavity pressure was measured by inserting a steel cannula through a drill hole in the cortex into the marrow cavity. The bones studied were mainly the tibia and femur. During the normal control condition, the marrow cavity pressure was found to have a wide range from animal to animal. In the rabbits, the range was from 20 to 60 mm. Hg. (15 to 50 percent of the systemic blood pressure). In the dogs, it ranged from 40 to 120 mm. Hg. (20 to 90 percent of the systemic blood pressure). However, the systemic blood pressure, intramedullary pressure and nutrient venous outflow were remarkably constant in a control period, therefore, their changes under experimental conditions were readily recordable. Various factors affecting bone circulation were studied. If the femoral vein is occluded the marrow cavity pressure rises and the nutrient venous outflow increases indicating venous congestion of bone. Nutrient artery occlusion causes a sharp fall in marrow cavity pressure coupled with a marked decrease in the nutrient venous outflow. Adrenalin and noradrenalin intravenous infusions produce a fall in marrow cavity pressure coupled with a decreased bone blood flow, despite an elevation in the systemic blood pressure. Isoproterenol hydrochloride generally causes a fall in the systemic blood pressure, widening of the pulse pressure, a fall in the marrow cavity pressure and a decrease in the nutrient venous outflow. Electrical sympathetic stimulation produces a fall in the marrow cavity pressure and a decrease in bone blood flow. Lumbar sympathectomy causes a rise in the marrow cavity pressure and an increase in the bone blood flow. Skeletal muscle contraction produces bone venous congestion with elevation of the marrow cavity pressure and increased nutrient venous outflow. Muscular relaxation causes a momentary sharp fall in the marrow cavity pressure to sub control levels before returning to the normal pressure. It is concluded that the marrow cavity pressure is bone blood flow dependent and reflects well the changes in the hemodynamics of bone. The narrow pressure rises if the arterial blood supply to bone increases or the venous congestion occurs in bone. The marrow pressure falls if the arterial blood supply to bone decreases or the venous drainage of bone is facilitated. / Surgery, Department of / Medicine, Faculty of / Graduate

Le débit sanguin et sa régulation sont des indicateurs importants de la santé des tissus. Leur mesure a de nombreuses applications en recherche fondamentale et clinique. Certaines techniques optiques constituent un moyen intéressant pour la mesure du débit sanguin, car en général elles sont peu invasives et relativement abordables car elles utilisent des systèmes d'illumination continus. Pendant ma thèse, j'ai contribué au développement de techniques de suivi de la circulation sanguine dans des modèles animaux avec la construction d'un dispositif multimodal basé sur la fluxmétrie laser et sur l'imagerie des signaux optiques intrinsèques, capable de mesurer les paramètre hémodynamiques microvasculaire au niveau superficiel du cerveau. Ce dispositif, testé sur des modèles animaux d'accident vasculaire cérébral, est adaptable et peut être utilisé à d'autres fins. En parallèle, j'ai mis au point des nouvelles méthodes expérimentales et des protocoles de traitement d'images qui ont permis de réaliser des études longitudinales. En outre, ce dispositif a été utilisé dans une étude multidisciplinaire pour comprendre le rôle d'une protéine impliquée dans le cas de lésions de reperfusion après un accident vasculaire cérébral ischémique dans des modèles animaux. Ma contribution majeure réside dans le développement de l'imagerie de contraste de speckle spectroscopique et tomographique, nouvelle technique d'imagerie 3D non invasive pour la mesure du débit sanguin en profondeur. Dans l'ensemble, ces contributions permettront le développement de méthodes tomographiques non invasives rentables pour la mesure du débit sanguin chez l'homme. / Blood flow and its regulation are important for the health of tissues and its measurement has many applications in research and clinical environments. Optical techniques are often attractive for the non- or minimally-invasive, continuous and relatively inexpensive measurement of blood flow. This work contributes to the monitoring of blood flow in translational research with the construction of a multimodal device, based on laser speckle flowmetry and optical intrinsic signals, capable of measuring superficial microvascular cerebral blood flow, blood oxygenation and blood volume. This device was applied in animal models of ischemic stroke and is flexible to be modified and used for other purposes. In doing so, I have developed new experimental methods and image processing protocols that allowed us to perform longitudinal studies where the animal can be removed from the device several times. This device has also been used to elucidate the role of the Mannose-binding lectin protein in reperfusion injury after an ischemic stroke in animal models. This led to the main contribution of this work: the development of the speckle contrast optical spectroscopy and tomography, a new non-invasive, optical technique for deep blood flow measurement that paves the way for deeper and three dimensional imaging of blood flow. This new method was first developed from a theoretical perspective. Then it was validated in tissue simulating phantoms and demonstrated to be feasible in measurements on the human arm muscle. Overall, these contributions will allow the development of cost-effective, non-invasive tomographic methods for the measurement of blood flow even in humans.

INTRODUCTION: As populations are adopting a Western lifestyle, with high intake of dietary sugar and fat and low physical activity, the risk of developing Type 2 Diabetes is only increasing dramatically. Diabetes leads to drastic alterations within the body, primarily leading to neuropathies, nephropathies and retinopathies. As the prevalence of diabetes increases, it is important to understand the threat that it poses to the retina, and ultimately, vision. OBJECTIVE: We plan to compare the retina of diabetic patients with retinopathies to normal, healthy patients to understand the differences between them. We will be using a novel imaging technique, called Laser Speckle Flowgraphy, which provides the Mean Blur Rate, a value directly related to the blood flow velocity within the retina, specifically the optic nerve head. Using the calculated Mean Blur Rate, this study will quantify baseline blood flows in patients with diabetic retinopathies. This project aims to understand and differentiate the Mean Blur Rate of healthy patients and diabetic patients, including inter-patient and intra-patient comparisons, as well as changes in the Mean Blur Rate over time. The potential influence of treatment factors, such as intravitreal injection treatment or laser treatment, or demographic factors, such as age and race, on the Mean Blur Rate of diabetic retinopathy patients will also be evaluated. By understanding the difference in the retinas of diabetic patients and healthy patients, we can work towards preventing the loss of vision and function. METHODS: A total of 25 Type 2 diabetic patients with a diabetic retinopathy equaling 46 eyes were compared to 20 healthy patients, equaling 40 eyes. We collected the Mean Blur Rate for comparison between the two populations. Data was compared with correlation, t-test and ANOVA studies to find whether demographic or treatment variables influenced the Mean Blur Rate of diabetic retinopathy patients. RESULTS: We found a difference between the Mean Blur Rate, and thus blood flow, between the retina of diabetic and healthy patients. Diabetic patients tended to have a lower flow, presumably attributable the effects of hyperglycemia on blood circulation. Diabetic patients also have a significant difference in the Mean Blur Rate between both of their eyes, indicating that their hyperglycemia may affect both eyes differently (p<0). There was significant variability within both diabetic retinopathy patients and normal, healthy patients (p<0 for healthy patients and p<0.001 for diabetic patients). This is expected as blood circulation can be affected by a variety of factors other than disease status. We also found that the MBR of diabetics who were treated with intravitreal injections was on average higher than those who had not received intravitreal treatment. (p<0.05) CONCLUSION: Our study highlights how diabetic retinopathy impacts retinal blood flow, as well as showcases how Laser Speckle Flowgraphy can be used as a reliable method to measure and compare retinal blood velocities. Further studies are needed to understand how exactly diabetes affects blood circulation, although several theories are currently available. We also found a relation between previous intravitreal injection history and the blood flow velocity, but other studies have had mixed results on how exactly these injections alter the blood flow within the retina. Future studies can be conducted to better understand this relationship and uncover whether the effect on blood flow velocity is related to the drug used for the intravitreal injection or some other factor.