Increased blood viscosity8/10/2023 Blood viscosity increases with increased values of hematrocit. The percentage of blood volume occupied by red blood cells is defined as hematocrit. As a result, the organism produces more red blood cells which leads to an increase in blood viscosity. In this case, normal amount of red blood cells would not be sufficient to transport enough oxigen throughout the body. Populations living in high altitute areas, for instance, are exposed to rarified air. Under normal conditions red blood cells have the greatest effect on viscosity. The change in amount of any one of these components can lead to changes in viscosity. With the addition of red bood cells, white blood cells and platelets the viscosity is increased. Because of the different components of plasma and their interactions the viscosity is higher than water. Plasma is mostly water but also contains molecules such as electrolytes, proteins and other macromolecules. K - constant characterizing physical properties of particleīlood is a suspension of red blood cells, white blood cells and platelets in plasma. The equation to calculate the viscosity of a suspention is characterized by: An increase in temperature results in a decrease of viscosity. Viscosity in liquids depends on temperature and pressure. The unit for kinetic viscosity is m 2 s -1. The kinetic viscosity is defined as dynamic viscosity divided by the density: In some cases it is still possible to encounter the unit P (poise 1P= 1g x cm -1 x s -1), where 1 Pa x s= 10P and 1mPa x s =1 cP. The coefficient η is called dynamic viscosity. These liquids, where viscosity depends on velocity increase, are called non-newtonian fluids. Examples thereof are colloid solutions, suspensions and emulsions. For certain liquids, however, Newton’s equation is not valid. The liquids that fulfil this equation are called newtonian fluids. Since then, many experiments have confirmed the validity of this equation for most liquids. This concept was first formulated by Isaac Newton. In laminar flow, this tension is defined by the liquid viscosity times the velocity gradient: In this case a tangential tension (or shear stress) arises between the layers. This produces a velocity gradient: difference of velocity between the layers divided by the perpendicular distance between them (dv/dy). On the other hand the latter will then delay the former. In two parallel liquid layers with different velocities the layer with greater velocity tends to pull the layer with lesser velocity. Viscosity in newtonian and non-newtonian fluids The absence of internal friction ( ideal fluid) equals zero viscosity.įluids with smaller viscosity values are closer to ideal fluids. Hence, the greater the internal friction is, the higher is the viscosity. Greater internal friction results in slower fluid’s velocity and greater resistance to movement. As we focus our attention further away from the walls it is possible to observe an increase in the flow’s velocity. The layer of water adheres to the walls of the tube seeming immobile. Let us consider an open tube and water flowing through it: 2 Viscosity in newtonian and non-newtonian fluids.In the treatment of high blood viscosity disorders it is suggested that the immunosuppressant drug, Thiamphenicol, may be useful because of its ability to induce a reversible dose-related depression of erythropoiesis, and thereby reduce blood viscosity. This is considered to be the mechanism of proteinuria. In order to overcome the peripheral resistance, intravascular pressure rises, and if adequate pressures develop, plasma proteins may deform and pass through the vascular basement membrane. The physiological significance of increased blood viscosity lies in the associated increase in peripheral vascular resistance which develops because of altered blood rheology. On the basis that all basement membranes exhibit biological thixotropy, it has been suggested that basement membranes are pressure dependent. Currently accepted concepts of renal and vascular physiology are inadequate to explain the reversible increases in vascular permeability which occur during episodes of increased blood viscosity.
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