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Blood viscosity

From Wikipedia, the free encyclopedia

Blood viscosity is a measure of the resistance of blood to flow, which is being deformed by either shear or extensional strain.

Blood is a liquid that consists of plasma and particles, such as the red blood cells. The viscosity of blood thus depends on the viscosity of the plasma, in combination with the hematocrit. However, plasma can be considered a Newtonian fluid, but blood cannot due to the red blood cells which add non-idealties to the fluid. The fluid must reach a shear rate of about 100 (1/sec) to be assumed Newtonian. Until this point is reached the term viscosity cannot be applied to blood. The viscosity of blood after this shear rate is reached is about five times as great as the viscosity of water. When the hematocrit rises to 60 or 70, which it often does in polycythemia,^[1] the blood viscosity can become as great as 10 times that of water, and its flow through blood vessels is greatly retarded because of increased resistance to flow.^[2] This will lead to decreased oxygen delivery.^[3]

In pascal-seconds (Pa·s), the viscosity of blood at 37°C is normally 3*10^-3 to 4*10^-3.^[4] The analogous unit in the centimetre gram second system of units is Poise, and the viscosity of blood at 20°C is normally 10 centipoise (cP).^[5]

Plasma's viscosity is determined by water-content and macromolecular components, so these factors that affect blood viscosity are the plasma protein concentration and types of proteins in the plasma, but these effects are so much less than the effect of hematocrit that they are not significant,^[6] and elevation of plasma viscosity correlates to the progression of coronary and peripheral vascular diseases.^[6][1] Anemia can lead to decrease blood viscosity, which may lead to heart failure.

Other factors influencing blood viscosity include temperature, where an increase in temperature results in a decrease in viscosity. This is particularly important in hypothermia, where an increase in blood viscosity will cause problems with blood circulation.

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• 呵呵 protein!!! not glucose!!!! -puttwocentsin- ♀ (18565 bytes) () 12/12/2011 postreply 12:11:12