Plasma viscosity

Plasma viscosity and blood viscosity are not the same thing, but are closely related. The plasma makes the blood flowable because it consists mainly of water. When the cellular plasma components increase, the blood can lose its physiological viscosity.

What is the plasma viscosity?

Viscosity is a measure that describes the viscosity of fluids. The higher the viscosity, the thicker or more viscous the fluid. Viscous fluids combine fluid properties with material properties. If the viscosity is high, the individual molecules of a fluid are all the more closely linked. This makes you more immobile and the liquid has less flowability.

Viscous liquids do not behave as Newtonian fluids, i.e. not proportionally. Viscosity occurs in different milieus of the human body, for example the blood. Accordingly, human blood does not behave like a Newtonian fluid, but shows an adaptable and erratic flow behavior, which is determined by the Fåhraeus-Lindqvist effect.

In vessels with a narrow lumen, for example, the viscous blood has a different consistency than in vessels with a wide lumen. These connections 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 in particular, for example, by the plasma level of fibrinogen. In addition, the plasma viscosity changes with temperature. Since the plasma is more fluid, it improves the flow properties of the blood.

So-called hemodynamics deals with the plasma viscosity, the blood viscosity and the relevant factors.

Function & task

The 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 the vascular elasticity of the blood vessels are just as decisive factors in this context as the lumen of the blood vessels.

All of the above factors influence each other. A change in the blood volume, the lumen, the vascular elasticity, the blood pressure or the cardiac output therefore has an effect on the viscosity of the blood. The same applies in the opposite direction. In addition, the blood viscosity depends on the [[hematocrit, the temperature, the erythrocytes and their malleability. The viscosity of the blood is determined by many physical and chemical properties.

The blood viscosity ultimately contributes to ideally controlling the blood flow in the body to cover individual organs and tissues as required.

Unlike other fluids in the human body, the blood does not behave as a Newtonian fluid in terms of its flow behavior, i.e. it does not flow linearly. Instead, its erratic flow behavior is primarily determined by the Fåhraeus-Lindqvist effect. The effect changes the viscosity of the blood as a function of the vessel diameter. In small-diameter vessels, the blood is less viscous. This prevents capillary stasis. The blood viscosity is thus characterized by differences at different points in the bloodstream.

The basis for the Fåhraeus-Lindquist effect is the deformability of the red blood cells. In the vicinity of the vessel walls, shear forces occur which displace the erythrocytes into the axial flow. This axial migration of the red blood cells creates a marginal flow with few cells. The edge flow of the plasma serves as a kind of sliding layer that makes the blood appear more fluid.

Plasma consists of around 93 percent water and contains around seven percent proteins, electrolytes, nutrients and metabolic metabolites. In this way, plasma ultimately liquefies the blood, lowers its viscosity and creates better flow properties for the red blood cells. Since the plasma viscosity has a retroactive effect on the blood viscosity, all changes in the plasma viscosity have consequences for the flow properties of the blood itself.

Illnesses & ailments

The blood viscosity is determined in viscometry. The measuring method determines the flow speed based on the temperature and pressure-dependent flow capacity and the resistance as well as the internal friction. The viscosity of plasma can in turn be measured using a capillary viscometer. In contrast to the determination of the 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 flow in body tissues. Thus, abnormal plasma viscosity can have serious consequences for the nutrient and oxygen supply of all body tissues.

A pathological change in plasma viscosity is in most cases associated with serious diseases. The so-called hyperviscosity syndrome can occur in this context. Changes in plasma viscosity mostly depend on changes in the concentration of plasma proteins. An increase in plasma proteins also occurs in the context of hyperviscosity syndrome. In this clinical complex of symptoms, the paraprotein concentration of the plasma in particular increases, as a result of which the blood viscosity increases and the fluidity decreases.

The hyperviscosity syndrome can occur in the context of Waldenström's disease. With this symptom complex, the IgM concentration of the blood increases. The IgM molecule is a large molecule made up of Y-shaped units that causes hyperviscosity syndrome to develop at plasma concentrations of 40 g / l.

Hyperviscosity syndromes due to increased paraprotein levels also characterize malignant diseases. In addition to multiple myeloma, a benign disease can also provide the framework for the increase in viscosity 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 which impair the plasma viscosity and the flow behavior of the blood. Since the flow properties of blood can also change through immobilization, pathological agglomerations of red blood cells often occur in immobile patients.