Fåhræus–Lindqvist effect

Fåhræus–Lindqvist effect refers to the phenomenon where the viscosity of blood decreases as it flows through smaller blood vessels. This effect, first described by Swedish scientists Robin Fåhræus and Torsten Lindqvist in the 1930s, has significant implications for the understanding of blood flow and its mechanics within the microcirculation system of the body. The Fåhræus–Lindqvist effect complements the Fåhræus effect, which describes how the average concentration of red blood cells (RBCs) decreases as blood moves through capillaries, leading to a reduction in blood viscosity.

Mechanism

The Fåhræus–Lindqvist effect occurs primarily due to the axial migration of red blood cells within the blood vessels. As blood flows through small-diameter vessels (less than 300 micrometers), red blood cells tend to move towards the center of the vessel, leaving a cell-free layer near the walls. This layer significantly reduces the friction between the moving blood and the vessel walls, thereby decreasing the overall viscosity of the blood within these small vessels. The effect is more pronounced in vessels with diameters less than 100 micrometers, such as in arterioles and capillaries.

Physiological Significance

The reduction in blood viscosity due to the Fåhræus–Lindqvist effect facilitates more efficient blood flow through the microvasculature. This efficiency is crucial for the delivery of oxygen and nutrients to tissues and the removal of carbon dioxide and metabolic wastes. It also plays a role in reducing the workload on the heart, as the heart does not need to exert as much pressure to maintain blood flow through the narrower vessels.

Clinical Implications

Understanding the Fåhræus–Lindqvist effect is important in clinical settings, especially in the management of diseases affecting microcirculation, such as diabetes mellitus and hypertension. It also has implications in the development of artificial blood substitutes and in the design of microfluidic devices for medical diagnostics.

Related Phenomena

The Fåhræus–Lindqvist effect is closely related to other hemorheological phenomena, including the Fåhræus effect and shear thinning, where the viscosity of blood decreases with increasing shear rate. These phenomena collectively contribute to the complex behavior of blood flow in the circulatory system.