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Fåhræus–Lindqvist Effect
The Fåhræus–Lindqvist effect ( ) or sigma effect describes how the viscosity of blood changes with the diameter of the vessel it travels through. In particular there is a decrease in viscosity as the vessel diameter decreases, but only at small diameters of 10–300 micrometers (mainly capillaries). This is because erythrocytes move to the centre of the vessel, leaving only plasma near the wall of the vessel. History The effect was first documented by a German group in 1930. Shortly after, in 1931, it was reported independently by the Swedish scientists Robin Fåhræus (1888–1968) and Johan Torsten Lindqvist (1906–2007), after whom the effect is commonly named. Fåhræus was a pathologist and hematologist, Lindqvist was a physician. Fåhræus and Lindqvist published their article in the ''American Journal of Physiology'' in 1931 describing the effect. Their study represented an important advance in the understanding of hemodynamics which had widespread implications f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shear Rate
In physics, mechanics and other areas of science, shear rate is the rate at which a progressive shear strain is applied to some material, causing shearing to the material. Shear rate is a measure of how the velocity changes with distance. Simple shear The shear rate for a fluid flowing between two parallel plates, one moving at a constant speed and the other one stationary ( Couette flow), is defined by :\dot\gamma = \frac, where: *\dot\gamma is the shear rate, measured in reciprocal seconds; * is the velocity of the moving plate, measured in meters per second; * is the distance between the two parallel plates, measured in meters. Or: : \dot\gamma_ = \frac + \frac. For the simple shear case, it is just a gradient of velocity in a flowing material. The SI unit of measurement for shear rate is s−1, expressed as "reciprocal seconds" or " inverse seconds". However, when modelling fluids in 3D, it is common to consider a scalar value for the shear rate by calculating the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vascular Resistance
Vascular resistance is the resistance that must be overcome for blood to flow through the circulatory system. The resistance offered by the systemic circulation is known as the systemic vascular resistance or may sometimes be called by another term total peripheral resistance, while the resistance caused by the pulmonary circulation is known as the pulmonary vascular resistance. Vasoconstriction (i.e., decrease in the diameter of arteries and arterioles) increases resistance, whereas vasodilation (increase in diameter) decreases resistance. Blood flow and cardiac output are related to blood pressure and inversely related to vascular resistance. Measurement The measurement of vascular resistance is challenging in most situations. The standard method is by the use of a Pulmonary artery catheter. This is common in ICU settings but impractical is most other settings. Units for measuring Units for measuring vascular resistance are dyn·s·cm−5, pascal seconds per cubic metre (Pa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Whole Blood
Whole blood (WB) is human blood from a standard blood donation. It is used in the treatment of massive bleeding, in exchange transfusion, and when people donate blood to themselves (autologous transfusion). One unit of whole blood (approximately 450 mL) increases hemoglobin levels by about 10 g/L. Cross matching is typically done before the blood is given. It is given by injection into a vein. Side effects include red blood cell breakdown, high blood potassium, infection, volume overload, lung injury, and allergic reactions such as anaphylaxis. Whole blood is made up of red blood cells, white blood cells, platelets, and blood plasma. It is best within a day of collection; however, it can be stored for up to three weeks if refrigerated (1-6 °C). The blood is typically combined with an anticoagulant and preservative during the collection process. The first transfusion of whole blood was in 1818; however, common use did not begin until the First and Second World ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Effective Viscosity
In fluid mechanics, apparent viscosity (sometimes denoted ) is the shear stress applied to a fluid divided by the shear rate: :\eta = \frac For a Newtonian fluid, the apparent viscosity is constant, and equal to the Newtonian viscosity of the fluid, but for non-Newtonian fluids, the apparent viscosity depends on the shear rate. Apparent viscosity has the SI derived unit Pa·s ( Pascal-second), but the centipoise is frequently used in practice: (1 mPa·s = 1 cP). Application A single viscosity measurement at a constant speed in a typical viscometer is a measurement of the instrument viscosity of a fluid (not the apparent viscosity). In the case of non-Newtonian fluids, measurement of apparent viscosity without knowledge of the shear rate is of limited value: the measurement cannot be compared to other measurements if the speed and geometry of the two instruments is not identical. An apparent viscosity that is reported without the shear rate or information about the instrument ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Red Blood Cell
Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cell and the vertebrate's principal means of delivering oxygen () to the body tissue (biology), tissues—via blood flow through the circulatory system. Erythrocytes take up oxygen in the lungs, or in fish the gills, and release it into tissues while squeezing through the body's capillary, capillaries. The cytoplasm of a red blood cell is rich in hemoglobin (Hb), an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells and the blood. Each human red blood cell contains approximately 270 million hemoglobin molecules. The cell membrane is composed of proteins and lipids, and this structure provides properties essential for physiological Cell (biology), cell function such as erythrocyte deformabil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hematocrit
The hematocrit () (Ht or HCT), also known by several other names, is the volume percentage (vol%) of red blood cells (RBCs) in blood, measured as part of a blood test. The measurement depends on the number and size of red blood cells. It is normally 40.7–50.3% for males and 36.1–44.3% for females. It is a part of a person's complete blood count results, along with hemoglobin concentration, white blood cell count and platelet count. Because the purpose of red blood cells is to transfer oxygen from the lungs to body tissues, a blood sample's hematocrit—the red blood cell volume percentage—can become a point of reference of its capability of delivering oxygen. Hematocrit levels that are too high or too low can indicate a blood disorder, dehydration, or other medical conditions. An abnormally low hematocrit may suggest anemia, a decrease in the total amount of red blood cells, while an abnormally high hematocrit is called polycythemia. Both are potentially life-threatening d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluid
In physics, a fluid is a liquid, gas, or other material that may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are Matter, substances which cannot resist any shear force applied to them. Although the term ''fluid'' generally includes both the liquid and gas phases, its definition varies among branches of science. Definitions of ''solid'' vary as well, and depending on field, some substances can have both fluid and solid properties. Non-Newtonian fluids like Silly Putty appear to behave similar to a solid when a sudden force is applied. Substances with a very high viscosity such as Pitch (resin), pitch appear to behave like a solid (see pitch drop experiment) as well. In particle physics, the concept is extended to include fluidic matters other than liquids or gases. A fluid in medicine or biology refers to any liquid constituent of the body (body fluid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drag (physics)
In fluid dynamics, drag, sometimes referred to as fluid resistance, is a force acting opposite to the direction of motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers, two solid surfaces, or between a fluid and a solid surface. Drag forces tend to decrease fluid velocity relative to the solid object in the fluid's path. Unlike other resistive forces, drag force depends on velocity. Drag force is proportional to the relative velocity for low-speed flow and is proportional to the velocity squared for high-speed flow. This distinction between low and high-speed flow is measured by the Reynolds number. Drag is instantaneously related to vorticity dynamics through the Josephson-Anderson relation. Examples Examples of drag include: * Net force, Net Aerodynamic force, aerodynamic or Fluid dynamics, hydrodynamic force: Drag acting opposite to the direction of movement of a solid object such as cars, aircraft, and boat hulls. * Viscou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Experimental Data
Experimental data in science and engineering is data produced by a measurement, test method, experimental design or quasi-experimental design. In clinical research any data produced are the result of a clinical trial. Experimental data may be qualitative or quantitative, each being appropriate for different investigations. Generally speaking, qualitative data are considered more descriptive and can be subjective in comparison to having a continuous measurement scale that produces numbers. Whereas quantitative data are gathered in a manner that is normally experimentally repeatable, qualitative information is usually more closely related to phenomenal meaning and is, therefore, subject to interpretation by individual observers. Experimental data can be reproduced by a variety of different investigators and mathematical analysis may be performed on these data. See also * Accuracy and precision * Computer science * Data analysis * Empiricism * Epistemology * Informatic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radius
In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is the line segment or distance from its center to any of its Vertex (geometry), vertices. The name comes from the Latin ''radius'', meaning ray but also the spoke of a chariot wheel.Definition of Radius at dictionary.reference.com. Accessed on 2009-08-08. The typical abbreviation and mathematical symbol for radius is ''R'' or ''r''. By extension, the diameter ''D'' is defined as twice the radius:Definition of radius at mathwords.com. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pressure Drop
Pressure drop (often abbreviated as "dP" or "ΔP") is defined as the difference in total pressure between two points of a fluid carrying network. A pressure drop occurs when frictional forces, caused by the resistance to flow, act on a fluid as it flows through a conduit (such as a channel, pipe, or tube). This friction converts some of the fluid's hydraulic energy to thermal energy (i.e., internal energy). Since the thermal energy cannot be converted back to hydraulic energy, the fluid experiences a drop in pressure, as is required by conservation of energy. The main determinants of resistance to fluid flow are fluid velocity through the pipe and fluid viscosity. Pressure drop increases proportionally to the frictional shear forces within the piping network. A piping network containing a high relative roughness rating as well as many pipe fittings and joints, tube convergence, divergence, turns, surface roughness, and other physical properties will affect the pressure drop. Hig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
