Plasma viscosity and blood viscosity are not the same thing, but they are directly related. Plasma makes blood flowable because it is composed mainly of water. When cellular plasma components increase, blood may lose its physiologic viscosity.
What is plasma viscosity?
Plasma has special fluid mechanics that are determined by different forces. Viscosity is a measure that describes the viscosity of fluids. The higher the viscosity, the thicker or more viscous the fluid. Viscous fluids combine liquid properties with material properties. At high viscosity, the individual molecules of a fluid are more strongly bound together. This makes them more immobile and the fluid has less flowability. Viscous fluids do not behave as Newtonian fluids, i.e. they are not proportional. Viscosity is present in different environments of the human body, such as blood. Accordingly, human blood does not behave as a Newtonian fluid, but exhibits adaptive and erratic flow behavior governed by the Fåhraeus-Lindqvist effect. In vessels with a narrow lumen, for example, viscous blood has a different consistency than in vessels with a wide lumen. These relationships keep the erythrocytes from clumping together. The viscosity of blood plasma is called plasma viscosity. It depends on the concentration of the individual plasma proteins and is thus determined, for example, in particular by the plasma level of fibrinogen. In addition, plasma viscosity changes with temperature. Since plasma tends to be fluid, it improves the flow properties of the blood. The field known as hemodynamics is concerned with plasma viscosity, blood viscosity, and the factors relevant to it.
Function and task
Plasma has a special fluid mechanics that is determined by different forces. Parameters such as blood pressure, blood volume, cardiac output, plasma or blood viscosity, and vascular elasticity of the blood vessels are crucial factors in this context, as is the lumen of the blood vessels. All of the above factors influence each other. A change in blood volume, lumen, vascular elasticity, blood pressure or cardiac output thus has a feedback effect on blood viscosity. The same is true in the opposite direction. In addition, blood viscosity depends on [[hematocrit||, temperature, erythrocytes and their deformability. Thus, blood viscosity is determined by many physical and chemical properties. Ultimately, blood viscosity helps to ensure that the body’s blood flow is ideally controlled to cover individual organs and tissues as needed. Unlike other fluids in the human body, blood does not behave as a Newtonian fluid in terms of its flow behavior, so it does not flow linearly. Instead, its erratic flow behavior is determined primarily by the Fåhraeus-Lindqvist effect. The effect causes the viscosity of the blood to change as a function of the vessel diameter. In vessels of small diameter, the blood is less viscous. This prevents capillary stasis. Thus, blood viscosity is characterized by differences at different points in the circulation. The basis for the Fåhraeus-Lindquist effect is the deformability of red blood cells. In the vicinity of vessel walls, shear forces occur that displace the red blood cells into the axial flow. This axial migration of red blood cells gives rise to a cell-poor marginal flow. The plasma edge flow serves as a kind of sliding layer that makes the blood appear more fluid. Plasma consists of about 93 percent water and contains about seven percent proteins, electrolytes, nutrients and metabolites. In this way, plasma ultimately liquefies the blood, reduces its viscosity and creates better flow properties for the red blood cells. Because plasma viscosity feeds back on blood viscosity, any changes in plasma viscosity have consequences for the flow properties of the blood itself.
Diseases and ailments
Blood viscosity is determined in viscometry. The measurement method determines the flow velocity based on the flow capacity and resistance, each of which is dependent on temperature and pressure, as well as internal friction. The viscosity of plasma can in turn be measured using capillary viscometers.In contrast to the determination of blood viscosity, the effect of shear forces does not have to be included in the calculation. There is a close relationship between plasma viscosity, blood viscosity, flow dynamics and blood supply to body tissues. Thus, abnormal plasma viscosity can have serious consequences for the nutrient and oxygen supply to all body tissues. In most cases, a pathological change in plasma viscosity is associated with serious diseases. In the context of these, the so-called hyperviscosity syndrome may occur. Changes in plasma viscosity usually depend on changes in the concentration of plasma proteins. An increase in plasma proteins also occurs in the context of the hyperviscosity syndrome. In this clinical complex of symptoms, the paraprotein concentration of plasma increases in particular, which increases blood viscosity and decreases fluidity. Hyperviscosity syndrome may occur in the setting of Waldenström’s disease. In this symptom complex, the IgM concentration of the blood increases. The IgM molecule is a large molecule consisting of Y-shaped units that causes hyperviscosity syndrome to develop at plasma concentrations of 40 g/l. Hyperviscosity syndromes due to elevated paraprotein levels further characterize malignant diseases. In addition to multiple myeloma, benign disease may also provide the setting for viscosity elevation in individual cases. This is especially true for Felty’s syndrome, lupus erythematosus and rheumatoid arthritis. Other types of so-called immune complex diseases also lead to the deposition of immune complexes that affect plasma viscosity and blood flow properties. In addition, because the flow properties of blood can also be altered by immobilization, pathologic agglomerations of red blood cells often occur in immobile patients.
