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Thesis (doctoral)--Freie Universität Berlin, 1979.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted.

Thesis (M.Sc. (Applied Mathematics)) -- University of Limpopo, 2008 / Understanding the effects of blood viscosity variation plays a very crucial role in hemodynamics, thrombosis and inflammation and could provide useful information for diagnostics and therapy of (cardio) vascular diseases. Blood viscosity, which arises from frictional interactions between all major blood constituents, i.e. plasma, plasma proteins and red blood cells, constitutes blood inherent resistance to flow in the blood vessel. Generally, blood viscosity in large arteries is lower near the vessel wall due to the presence of plasma layer in this peripheral region than the viscosity in the central core region which depends on the hematocrit. In this dissertation, the flow of blood in a large artery is investigated theoretically using the fluid dynamics equations of continuity and momentum. Treating artery as a rigid channel with uniform width and blood as a variable viscosity incompressible Newtonian fluid, the basic flow structure and its stability to small disturbances are examined. A fourth-order eigenvalue problem which reduces to the well known Orr–Sommerfeld equation in some limiting cases is obtained and solved numerically by a spectral collocation technique with expansions in Chebyshev polynomials implemented in MATLAB. Graphical results for the basic flow axial velocity, disturbance growth rate and marginal stability curve are presented and discussed. It is worth pointing out that, a decrease in plasma viscosity near the arterial wall has a stabilizing effect on the flow.

Thesis--Copenhagen. / Summary in Danish. Includes bibliographical references (p. 117-133) and index.

Thesis--Copenhagen. / Summary in Danish. Includes index. Bibliography: p. 117-133.

The hematological and rheological characteristics of blood from a number of vertebrates was compared to assess possible species differences in blood viscosity that may influence cardiovascular oxygen transport. Nucleated red blood cells (RBCs) were more viscous (measured by cone-plate viscometry) in comparison with enucleate (mammalian) RBCs at hematocrits greater than 40% when measured at equivalent temperatures. The lower viscosity of enucleate RBCs is attributed to an enhanced deformability of enucleate cells in comparison to nucleated cells.

Stroke is a major health problem in all developed countries. These studies, performed in a stroke unit at a medical department, were designed to characterize essential clinical features of the different cerebrovascular disorders on admission to hospital, to evaluate the efficacy of admitting unselected stroke patients to a stroke unit and, to evaluate hemodilution as a therapeutical regime in patients with cerebral infarction. A prospective registry included 409 patients admitted to the stroke unit over a five-year period. Modern diagnostic equipment (CT scan and CSF analyses) and strict diagnostic criteria revealed a diagnostic distribution of 11% hemorrhagic, 76% ischemic cerebrovascular lesions and 13% TIAs. Mean age varied between 65.8 and 77.5 years in the various diagnostic groups with the highest in patients with embolic cerebral infarctions. Concomitant disorders affecting the cardiovascular system were highly prevalent and only 14% was free of such diseases prior to the stroke. In a comparative prospective study, over 16 months, no differences were found between patients treated in the stroke unit (n = 110) and the general medical wards (n = 183) regarding prognostic indicators on admission such as age, concomitant disorders and neurological symptoms. The stroke patients treated in the stroke unit had a statistically significant better prognosis regarding functional outcome and the need for long-term hospitalization was reduced up to one year after the stroke when compared to patients treated in general medical wards. All stroke patients seemed to benefit with the possible exception of patients in coma on admission. These results were achieved within the same or shorter length of initial hospital stay for patients in the stroke unit. Neither overall mortality, nor mortality in subgroups of prognostic importance was significantly affected by the stroke unit regime. Rapid hemodilution in the early phase of cerebral infarction by the combination of venesection and administration of dextran 40 was evaluated in a prospective controlled trial. After randomization 52 hemodi- luted and 50 control patients were comparable in prognostic variables. Signs of blood-brain-barrier breakdown and hemorrhagic admixture to the cerebrospinal fluid in the acute phase were less frequent in hemodiluted subjects. The hemodi luted patients showed a significantly higher degree of early improvement and fewer progressions. Neurological and functional disability in survivors and need for long-term hospitalization was significantly reduced at 3 months and at one year after the stroke compared to controls. Mortality was not affected. / digitalisering@umu

Red blood cells (RBCs) are the most abundant cells in human blood, representing 40 to 45% of the blood volume (hematocrit). These cells have the particular ability to deform and bridge together to form aggregates under very low shear rates. The theory and mechanics behind aggregation are, however, not yet completely understood. The purpose of this work is to provide a novel method to analyze, understand and mimic blood behaviour in microcirculation. The main objective is to develop a methodology to quantify and characterize RBC aggregates and hence enhance the current understanding of the non-Newtonian behaviour of blood at the microscale. For this purpose, suspensions of porcine blood and human blood are tested in vitro in a Poly-di-methylsiloxane (PDMS) microchannel to characterize RBC aggregates within these two types of blood. These microchannels are fabricated using standard photolithography methods. Experiments are performed using a micro Particle Image Velocimetry ( PIV) system for shear rate measurements coupled with a high speed camera for the flow visualization. Corresponding numerical simulations are conducted using a research Computational Fluid Dynamic (CFD) solver, Nek5000, based on the spectral element method solution to the incompressible non-Newtonian Navier-Stokes equations. RBC aggregate sizes are quantified in controlled and measurable shear rate environments for 5, 10 and 15% hematocrit. Aggregate sizes are determined using image processing techniques. Velocity fields of the blood flow are measured experimentally and compared to numerical simulations using simple non-Newtonian models (Power law and Carreau models). This work establishes for the first time a relationship between RBC aggregate sizes and corresponding shear rates in a microfluidic environment as well as one between RBC aggregate sizes and apparent blood viscosity at body temperature in a microfluidic controlled environment. The results of the investigation can be used to help develop new numerical models for non-Newtonian blood flow, provide a better understanding of the mechanics of RBC aggregation and help determine aggregate behaviour in clinical settings such as for degenerative diseases like diabetes and heart disease.