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	~~Hi, everybody~~! ~~My name is Gilbert~~. <br>It is a ~~little about myself: I live~~ in ~~France~~, ~~my city~~ of ~~Orleans~~. <br>~~It's called often Northern or cultural capital~~ of ~~CENTRE~~. ~~I've married 2 years ago~~.<br>~~I have~~ two ~~children - a son~~ (~~Abigail~~) and the ~~daughter~~ (~~Nona~~). ~~We all like Leaf collecting~~ and ~~pressing~~.<br>~~<br>My website;~~ [http://~~celebrity~~.~~0arr~~.com ~~celebrity gossips~~]		<!-- Deleted image removed: [[File:FLE2.jpg\|thumb\|right\|[[Red blood cell]]s flowing in a capillary. Cell free layer near the capillary walls contributes to lowering the [[viscosity]] in [[blood flow]] in small capillaries]] -->
			:''Should not be confused with "[[Fåhræus effect]]"''

			The '''Fåhræus–Lindqvist effect''' {{IPAc-en\|f\|ɑ:\|ˈ\|r\|eɪ\|.\|ə\|s\|_\|ˈ\|l\|ɪ\|n\|d\|k\|v\|ɪ\|s\|t}}<ref>[http://www.medilexicon.com/medicaldictionary.php?t=28015]</ref> is an effect where the [[viscosity]] of a fluid, in this case [[blood]], changes with the [[diameter]] of the tube it travels through; in particular there's a decrease of viscosity as the tube's diameter decreases (only if the vessel diameter is between 10 and 300 micrometers). This is because [[erythrocytes]] move over the center of the vessel, leaving [[blood plasma\|plasma]] at the wall of the vessel.

			== History ==
			The effect is named after Swedish scientists Robin Fåhræus and Torsten Lindqvist. Robert (Robin) Sanno Fåhræus was a Swedish [[pathologist]] and [[hematologist]], born on October 15, 1888, in [[Stockholm]]. He died on September 18, 1968, in [[Uppsala]], [[Sweden]]. Johan Torsten Lindqvist is a Swedish [[physician]], who was born in 1906 and died in 2007.<ref>{{cite book\|last=Lee Waite\|first=Jerry Fine\|title=Applied biofluid mechanics\|year=2007\|publisher=McGraw-Hill\|location=New York\|isbn=0-07-147217-7\|url=http://www.amazon.com/Applied-Biofluid-Mechanics-Lee-Waite/dp/0071472177}}</ref> Fåhræus and Lindqvist published an article in the [[American Journal of Physiology]] in 1931 describing the effect.<ref>{{cite book\|title=Fahraeus R, Lindqvist T (1931) The viscosity of the blood in narrow capillary tubes. The American Journal of Physiology 96:562–568}}</ref> Their study represented an important advance in the understanding of [[hemodynamics]] which had widespread implications for the study of human [[physiology]].
			They forced [[blood]] through fine [[glass]] [[capillary]] tubes connecting two reservoirs. Capillary [[diameters]] were less than 250 μm, and experiments were conducted at sufficiently high [[shear rate]]s (≥100 1/s) so that a similar flow in a large tube would be effectively [[Newtonian fluid\|Newtonian]]. After correcting for entrance effects, they presented their data in terms of an effective [[viscosity]], derived from fitting measured pressure drop and volume flow rate to [[Hagen–Poiseuille equation]] for a tube of radius '''''R'''''

			:<math> \ Q = \frac{ \pi R^4 \Delta P}{ 8 \mu_{e} L } </math>

			where:
			:<math>Q</math> is the [[volumetric flow rate]]
			:<math>\Delta P </math> is the [[pressure drop]] across the [[capillary]]
			:<math>L</math> is the length of capillary
			:<math> \mu_{e} </math> is the effective [[viscosity]]
			:<math>R</math> is the [[radius]]
			:[[pi\|<math> \pi </math>]] is the mathematical constant

			Although [[Hagen–Poiseuille equation]] is only valid for a [[Newtonian fluid]], fitting [[experimental data]] to this equation provides a convenient method of characterizing [[flow resistance]] by a single number, namely <math> \mu_{e} </math>. In general, <math> \mu_{e} </math> will depend on the [[fluid]] being tested, the [[capillary]] diameter, and the flow rate (or pressure drop). However, for a given fluid and a fixed [[pressure drop]], data can be compared between capillaries of differing [[diameter]].<ref>{{cite book\|last=Ethier\|first=C. Ross\|title=Introductory biomechanics : from cells to organisms\|year=2007\|publisher=Cambridge Univ. Press\|location=Cambridge [u.a.]\|isbn=0-521-84112-7\|url=http://www.amazon.com/Introductory-Biomechanics-Organisms-Biomedical-Engineering/dp/0521841127\|edition=Repr. with corrections\|coauthors=Simmons, Craig A.}}</ref>
			Fahraeus and Lindqvist noticed two unusual features of their data. First, <math> \mu_{e} </math> decreased with decreasing capillary radius, '''''R'''''. This decrease was most pronounced for capillary diameters < 0.5mm. Second, the tube [[hematocrit]] (i.e., the average [[hematocrit]] in the capillary) was always less than the [[hematocrit]] in the feed reservoir. The ratio of these two hematocrits, the tube relative [[hematocrit]], <math> H_{R} </math>,is defined as

			:<math> \mathrm{H_{R}} = { \mbox{tube hematocrit} \over \mbox{feed reservoir hematocrit}} </math>

			==Explanation of phenomena==

			These initially confusing results can be explained by the concept of a '''plasma cell-free layer''', a thin layer adjacent to the [[capillary]] wall that is depleted of [[red blood cell]]s. Because the cell-free layer is red cell-poor, its effective [[viscosity]] is lower than that of [[whole blood]]. This layer therefore acts to reduce flow resistance within the [[capillary]], with the net effect that the effective [[viscosity]] is less than that for whole blood. Because the cell-free layer is very thin (approximately 3 μm) this effect is insignificant in capillaries whose diameter is large.
			This explanation, while accurate, is ultimately unsatisfying, since it fails to answer the fundamental question of why a plasma cell-free layer exists. There are actually two factors which promote cell-free layer formation.
			# For particles flowing in a tube, there is a net [[hydrodynamic]] force that tends to force the particles towards the center of the [[capillary]]. This is known as the [[Segré–Silberberg effect]]. There are also effects associated with deformability of [[red blood cell]]s that might increase this force.
			# It is clear that [[red blood cell]]s cannot pass through the [[capillary]] wall, which implies that the centers of [[red blood cell]]s must lie at least one [[red blood cell]] half-thickness away from the wall. This means that, on average, there will be more [[red blood cell]]s near the center of the [[capillary]] than very near the wall.
			[[Cell-free marginal layer model]] is a [[mathematical model]] which tries to explain Fåhræus–Lindqvist effect mathematically.

			== Further reading ==
			* Schmidt, Lang (Hrsg.): ''Physiologie des Menschen: Mit Pathophysiologie'' (S. 623). Springer, Berlin; 30. Auflage 2007. ISBN 978-3-540-32908-4 {{de icon}}

			==See also==
			*[[Cell-free marginal layer model]]
			*[[Fåhræus effect]]
			*[[Blood viscosity]]
			*[[hemodynamics]]

			==References==
			{{Reflist}}

			{{DEFAULTSORT:Fahraeus-Lindqvist Effect}}
			[[Category:Blood]]

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Hi, everybody! My name is Gilbert. It is a little about myself: I live in France, my city of Orleans. It's called often Northern or cultural capital of CENTRE. I've married 2 years ago. I have two children - a son (Abigail) and the daughter (Nona). We all like Leaf collecting and pressing. My website; [http://celebrity.0arr.com celebrity gossips]

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