Robin Fahraeus: evolution of his concepts in cardiovascular physiology

Abstract

We give an account of the work of Robin Fåhraeus over the years 1917-1938, his contribution to our understanding of blood rheology, and its relevance to circulatory physiology. Fåhraeus published few original papers on this subject, yet he clearly understood the phenomena occurring in the tube flow of mammalian blood. 1) The concentration of cells in a tube less than 0.3 mm in diameter differs from that in the larger feed tube or reservoir, the Fåhraeus effect. This is due to a difference in the mean velocity of cells and plasma in the smaller vessel associated with a nonuniform distribution of the cells. 2) In tubes less than 0.3 mm in diameter, the resistance to blood flow decreases with decreasing tube diameter, the Fåhraeus-Lindqvist effect. We define and generalize the two effects and describe how red cell aggregation at low shear rates affects cell vessel concentration and resistance to flow. The fluid mechanical principles underlying blood cell lateral migration in tube flow and its application to Fåhraeus' work are discussed. Experimental data on the Fåhraeus and Fåhraeus-Lindqvist effects are given for red cells, white cells, and platelets. Finally, the extension of the classical Fåhraeus effect to microcirculatory beds, the Fåhraeus Network effect, is described. One of the explanations for the observed, very low average capillary hematocrits is that the low values are due to a combination of the repeated phase separation of red cells and plasma at capillary bifurcations (network effect) and the single-vessel Fåhraeus effect.

Controlled Microfluidic Environment for Dynamic Investigation of Red Blood Cell Aggregation

“…RBC aggregates can be altered by several factors such as the hematocrit (volume of RBCs in blood), the shear rate, the vessel diameter, the RBC membrane stiffness and the suspending medium composition [8][9][10] . Therefore, controlled conditions are required in order to effectively analyze the RBC aggregates.…”

Multiphase simulation of blood flow within main thoracic arteries of 8-year-old child with coarctation of the aorta

“…For the multiphase blood modelling with Euler-Euler technique, plasma and morphological elements are treated as continuous and interpenetrating phases. The EE approach is typically used for modelling narrow vessels where FahraeusLindqvist effect occurs [11][12][13][14]. It helps to estimate the RBC volume concentration in the aortic lumen while single phase modelling does not allow for this The current publication presents an application of a three-fluid Euler-Euler approach for modelling of blood flow within the aorta and its main thoracic branches of an 8-year-old patient suffering from coarctation of the aorta (in the modelling the flow through the coronary arteries was omitted).…”

Red blood cells in retinal vascular disorders

“…[1; 2; 3] In the early 20 th century, Robin Fåhraeus described the flow properties of the blood and reported, for the first time, altered suspension stability characteristics and fluidity of blood in the process of disease. [4] He explained humoral (RBC) pathology concepts on the basis of modern scientific approaches and introduced the Erythrocyte Sedimentation Rate (ESR), a test which is widely used across all the sub-specialities of medicine. Unfortunately, it was not until late 20 th century, that the medical fraternity began to accept the importance of the mechanics of blood flow and there was a significant increase in research effort looking at altered haemodynamics in almost all vascular disorders.…”

“…Throughout the vasculature, haematocrit varies on a vessel scale due to plasma skimming [80; 81] and the Fåhraeus effect. [4] Average shear rates in vessels vary by orders of magnitude. Stating that a given blood Furthermore, local distributions of RBCs, viewed in terms of a cell-free layer (CFL) [82; 83], cell-depleted layer (CDL) [84; 85] or a continuous distribution [15; 86; 87; 88] vary significantly.…”