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Blood Flow Mechanics
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
Blood viscosity is a measure of blood’s resistance to deformation by shear stress. In layman’s terms, it describes the “stickiness” of blood. Blood viscosity is a determining factor in cardiovascular dynamics. For example, the work required for the heart to pump blood increases with higher blood viscosity. In arterial blood flow, in which the shear rate is normally higher than 100 s−1, it is generally assumed that blood is Newtonian, that is, it has a constant viscosity. The Newtonian assumption is widely used in cardiovascular mechanics and generally provides a good estimation of the physiological parameters sought, such as vascular resistance and blood perfusion. The Newtonian approximation assumes that the fluid stress is linearly dependent on the applied rate of strain, where the viscosity is the proportionality coefficient. The relationship between the viscous stress and the deformation rate of the fluid element for an incompressible Newtonian fluid is given by: () τij=μ(∂ui∂xj+∂uj∂xi),
Analytical Applications of Filtration
Published in Michael J. Matteson, Clyde Orr, Filtration, 2017
Aggregates of blood elements may, during storage for future transfusion, become sufficiently large to occlude smaller arterioles, venules, capillaries, and other smaller conduits of the vascular system. These are not normally detected in the conventional capillary tube and cone-plate methods of measuring blood viscosity. Also, these smaller aggregates have been observed during hypotensive and endotoxin shock, following high-fat meals and following the addition of high-molecular-weight substances, serotonin, and certain diphosphates to blood.
Aggregation and blood flow in health and disease
Published in Annie Viallat, Manouk Abkarian, Dynamics of Blood Cell Suspensions in Microflows, 2019
Viviana Clavería, Christian Wagner, Philippe Connes
Blood viscosity is an important determinant of local flow characteristics. Blood exhibits shear thinning behavior: i.e., its viscosity decreases exponentially with increasing shear rates. In addition, blood has visco-elastic and thixotropic properties, which also affect local hemodynamics. A thixotropic fluid is a fluid whose viscosity is a function not only of the shearing condition, but also of the previous history of motion within the fluid [151]. Indeed, for a given flow and shear rate (γ˙), blood viscosity usually decreases with the length of time the fluid is in motion. The relative contribution of RBCs is represented by the hematocrit (Hct) value. A rise in Hct increases blood viscosity at all γ˙ and thixotropy, more particularly at low γ˙, like in veins and venules [20,151]. The shear thinning and non-Newtonian behavior of blood is determined primarily by the mechanical properties of circulating RBCs. There are two unique RBC characteristics that are primarily responsible for this non-Newtonian behavior: RBC deformability and RBC aggregation (see Figure 6.6, [35,93]).
Influence of relative humidity and temperature on human whole blood drying
Published in Drying Technology, 2023
Houssine Benabdelhalim, David Brutin
Whole human blood is a fluid composed of a solid cellular component, red blood cells (97%), white blood cells, and platelets. The volatile liquid part, plasma, contains water (92%) and proteins (8%).[18] Blood is a fluid tissue that is permanently transported in a unidirectional flow imposed by the cardiac pump. Red blood cells are the most abundant biocolloids, and their volume concentration is given by a dimensionless quantity, the hematocrit. For a healthy person, the hematocrit level varies between 38% and 50%.[18] Human whole blood is a viscoelastic non-Newtonian fluid characterized by shear-thinning behavior.[3] Its viscosity decreases with the imposed shear rate until reaching a Newtonian plateau at high shear rates. The blood viscosity is a function of biochemical composition, hematocrit level of blood, and temperature. The blood can be defined as a colloidal suspension in which the cells represent the solid phase. Also, as an emulsion, considering the deformation and aggregation of red blood cells. Human blood has two other non-Newtonian characteristics: the existence of yield stress and time dependence behavior (thixotropy).[3] Whole human blood has an average density of 1060 kg/m3 and a surface tension of N/m at 22C.[5]
Effect of magnetic field on haemodynamic perturbations in atherosclerotic coronary arteries
Published in Journal of Medical Engineering & Technology, 2018
Ashkan Javadzadegan, Abouzar Moshfegh, Masud Behnia
Pathophysiological changes in blood rheology is another risk factor for atherosclerosis. Elevated blood viscosity as the main rheological factor has been proposed as the aetiology of atherosclerosis [12,13]. This is because the blood viscosity is the key parameter in regulating haemodynamic forces such as blood flow shear stress and blood pressure.