Fåhraeus-Lindqvist effect

Of the Fåhraeus-Lindqvist effect is a phenomenon of blood flow that is based on the fluidity of the erythrocytes and is related to the viscosity of the blood. The viscosity is lower in vessels of the circulatory periphery with a narrow lumen than in vessels with a higher lumen. The Fåhraeus-Lindqvist effect primarily prevents blood congestion in the capillaries.

What is the Fåhraeus-Lindqvist Effect?

Human blood has a certain viscosity. The viscosity corresponds to a measure of the viscosity of body fluids. The thinner a liquid, the lower its viscosity. An alternative is to measure viscosity by means of stretching.

The concept of the Fåhraeus-Lindqvist effect describes a decrease in blood viscosity that is associated with a decreasing diameter of the vessels and thus a decreasing expansion. The vessel diameter drops below 300 µm and thus prevents blood congestion in the capillaries.

The Fåhraeus-Lindqvist effect is based on the natural properties and abilities of the erythrocytes. The phenomenon is considered to be the reason why the viscosity of the blood in vessels of the circulatory periphery is considerably lower because of the narrow lumen than in vessels of the central circulatory system with a higher lumen. The deformability of the blood cells associated with the effect is also known as fluidity and is a prerequisite for the Fåhraeus-Lindquist effect.

Function & task

The red blood cells are also called erythrocytes and have a certain fluidity. So you can deform. The deformation is due to the shear forces that the blood cells experience near the walls of the blood vessels. The resulting shear forces displace the erythrocytes. This is how the red blood cells migrate into the axial flow. This phenomenon is also known as axial migration and creates marginal currents with few cells.

The cells are washed around by a marginal current of plasma. In the Fåhraeus-Lindquist effect, this marginal current takes on the role of a sliding layer. Apparently the blood flows more fluidly in these areas. This relationship is related to the influence of hematocrit on the level of peripheral resistance. The hematocrit corresponds to the volume fraction of cellular blood elements. Red blood cells make up 96 percent of this and make up the largest proportion. The peripheral resistance corresponds to the flow resistance in the body's blood circulation and results from the sum of all peripheral vascular resistances.

The Fåhraeus-Lindqvist effect lowers the hematocrit influence on the peripheral resistance in smaller blood vessels below 300 µm. The phenomenon also reduces the frictional resistance in these vessels.

In larger blood vessels, on the other hand, there is high friction between the flowing cells. The cell-poor marginal current does not spread effectively in larger cells. This relationship increases the viscosity of the blood. This viscosity increases even in extremely narrow capillaries. Although the erythrocytes have fluidity, after a certain point they cannot deform any further. In summary, the apparent blood viscosity in vessels of up to ten micrometers due to the Fåhraeus-Lindqvist effect is only slightly higher than in plasma.

The decrease in viscosity is due to the erythrocytes, which move faster in the center of the bloodstream because of the smaller shear forces. For this reason, they increasingly move closer to the center, which is known as axial migration. In this way, a low-cell sliding layer is formed in the edge zone and the movement of the liquid in the center is accelerated. Because of their fluidity, erythrocytes can adapt to changed shear stresses and reduce any disturbing effects on hemodynamics.

Illnesses & ailments

Complaints related to the Fåhraeus-Lindqvist effect can have various causes. In most cases, disorders of the general hemodynamics are responsible for symptoms of this type. Such disorders can be related, for example, to pathological changes in the blood vessels.

Pathologically changed blood vessels can in turn be due to diseases such as arteriosclerosis. This slowly progressing disease often remains asymptomatic for many years and in many cases is diagnosed late. Blood lipids, thrombi or connective tissue are deposited in the blood vessels in arteriosclerosis and create plaques that narrow the vascular lumen. Such a restricted blood flow promotes secondary diseases.

In addition to or together with diseases such as arteriosclerosis, high vascular loads and the resulting cracks can cause disturbances in blood flow and the Fåhraeus-Lindqvist effect. Bleeding through cracks, for example, promotes the formation of thrombi. The blood vessels lose their elasticity, become rigid and harden noticeably.

The Fåhraeus-Lindqvist effect can also be impaired if the composition of the blood changes. This is the case, for example, with a lack of fluid. The same applies when taking certain medications, such as ovulation inhibitors. Increased coagulation factors after operations or major burns also change the composition of the blood.

Another conceivable connection for altered compositions is platelet aggregation. Thromboses are often favored by the phenomena mentioned. In addition to being overweight and old, the risk factors for thrombosis include regular nicotine or alcohol abuse, general hypertension and diabetes mellitus.

In addition, congenital red blood cell abnormalities can disrupt blood flow and with it the Fåhraeus-Lindqvist effect. Genetic changes in connection with the red blood cells show up, for example, in the context of sickle cell anemia, which is associated with a sickle-shaped shape of the red blood cells. In addition, metabolic diseases and iron or vitamin deficiencies have negative effects on the erythrocyte balance.

Since the Fåhraeus-Lindqvist effect prevents blood congestion in the capillaries, disturbances in the effect may lead to capillary blood congestion and are often initially noticeable as reddening of the skin or protruding veins.