Editing Perfusion

{{short description| Passage of fluid through the circulatory or lymphatic system to an organ or tissue }}
{{for|the journal|Perfusion (journal)}}

[[File:Lindbergh perfusion pump in Putnam Gallery, 2009-11-24.jpg|thumb|upright|A [[Charles Lindbergh|Lindbergh]] perfusion pump, {{circa|1935}}, an early device for simulating natural perfusion]]

'''Perfusion''' is the passage of fluid through the [[circulatory system]] or [[lymphatic system]] to an [[organ (anatomy)|organ]] or a [[tissue (biology)|tissue]],<ref>American Psychological Association (APA):
perfusion. (n.d.). Dictionary.com Unabridged (v 1.1). Retrieved March 20, 2008, from Dictionary.com website: http://dictionary.reference.com/browse/perfusion</ref> usually referring to the delivery of [[blood]] to a [[capillary]] bed in tissue. Perfusion may also refer to fixation via perfusion, used in histological studies. Perfusion is measured as the rate at which blood is delivered to tissue,<ref>{{cite journal  |vauthors=Thomas DL, Lythgoe MF, Pell GS, Calamante F, Ordidge RJ |title=The measurement of diffusion and perfusion in biological systems using magnetic resonance imaging. |journal=Phys Med Biol | date=2000| volume=45 | issue=8| pages=R97–138 |pmid = 10958179 | doi=10.1088/0031-9155/45/8/201}}</ref> or volume of blood per unit time (blood [[volumetric flow rate|flow]]) per unit tissue mass. The [[SI unit]] is m<sup>3</sup>/(s·kg){{citation needed|date=March 2021}}, although for human organs perfusion is typically reported in ml/min/g.<ref>{{cite journal  |vauthors=Engblom H, Xue H, Akil S, Carlsson M, Hindorf C, Oddstig J, Hedeer F, Hansen MS, Aletras AH, Kellman P, Arheden H |title=Fully quantitative cardiovascular magnetic resonance myocardial perfusion ready for clinical use: a comparison between cardiovascular magnetic resonance imaging and positron emission tomography. |journal=J Cardiovasc Magn Reson |date=2017 |volume=19 |issue=1 |pages=78 |pmid = 29047385 |doi=10.1186/s12968-017-0388-9|pmc=5648469 |doi-access=free }}</ref> The word is derived from the French verb ''perfuser'', meaning to "pour over or through".<ref name=OnlinePerfusion>{{cite web|title=Perfusion > What is Perfusion?|url=http://www.perfusion.com/cgi-bin/absolutenm/templates/articledisplay.asp?articleid=1548#.VKv4idKrqQM|publisher=[[Cardiovascular Perfusion Forum]]}}</ref> All animal tissues require an adequate blood supply for [[health]] and [[life]]. Poor perfusion (malperfusion), that is, [[ischemia]], causes health problems, as seen in [[cardiovascular disease]], including [[coronary artery disease]], [[cerebrovascular disease]], [[peripheral artery disease]], and many other conditions.

Tests verifying that adequate perfusion exists are a part of a patient's assessment process that are performed by [[medical]] or emergency personnel.  The most common methods include evaluating a body's [[skin]] color, [[body temperature|temperature]], condition (dry/soft/firm/swollen/sunken/etc), and [[capillary refill]].

During major surgery, especially [[cardiothoracic surgery]], perfusion must be maintained and managed by the [[health professional]]s involved, rather than left to the body's [[homeostasis]] alone. As the lead surgeons are often too busy to handle all [[hemodynamics|hemodynamic]] control by themselves, specialists called [[perfusionist]]s manage this aspect. There are more than one hundred thousand perfusion procedures annually.<ref name=Perfusion>{{cite web |title=Perfusion > Perfusion Services |url=http://www.specialtycare.net/services/perfusion/ |publisher=Specialty Care Services Group |access-date=2017-01-02 |archive-date=2018-12-17 |archive-url=https://web.archive.org/web/20181217175649/http://www.specialtycare.net/services/perfusion/ |url-status=dead }}</ref>

==Discovery==
In 1920, [[August Krogh]] was awarded the [[Nobel Prize in Physiology or Medicine]] for his discovering the mechanism of regulation of [[capillaries]] in [[skeletal muscle]].<ref>{{Cite journal | last1 = Larsen | first1 = E. H. | title = August Krogh (1874–1949): 1920 Nobel Prize | journal = Ugeskrift for Laeger | volume = 169 | issue = 35 | pages = 2878 | year = 2007 | pmid = 17877986}}</ref><ref>{{Cite journal | last1 = Sulek | first1 = K. | title = Nobel prize for August Krogh in 1920 for his discovery of regulative mechanism in the capillaries | journal = Wiadomosci Lekarskie  | volume = 20 | issue = 19 | pages = 1829 | year = 1967 | pmid = 4870667}}</ref> Krogh was the first to describe the adaptation of blood perfusion in muscle and other organs according to demands through the opening and closing of [[arterioles]] and [[capillaries]].{{citation needed|date=January 2014}}

==Malperfusion==

'''Malperfusion''' can refer to any type of incorrect perfusion though it usually refers to hypoperfusion. The meaning of the terms "overperfusion" and "underperfusion" is relative to the average level of perfusion that exists across all the tissues in an individual body. Perfusion levels also differ from person to person depending on metabolic demand.{{citation needed|date=March 2021}}

Examples follow:{{citation needed|date=March 2021}}
* [[Heart]] tissues are considered overperfused because they normally are receiving more blood than the rest of tissues in the organism; they need this blood because they are constantly working.
* In the case of skin cells, extra blood flow in them is used for [[thermoregulation]] of a body.  In addition to delivering [[oxygen]], blood flow helps to [[Dissipation|dissipate]] heat in a body by redirecting warm blood closer to its surface where it can help to cool a body through [[sweating]] and [[thermal dissipation]].
* Many types of [[tumor]]s, and especially certain types, have been described as "hot and bloody" because of their overperfusion relative to the body overall.

Overperfusion and underperfusion should not be confused with '''hypoperfusion''' and '''hyperperfusion''', which relate to the perfusion level relative to a tissue's current need to meet its metabolic needs. For example, hypoperfusion can be caused when an [[artery]] or [[arteriole]] that supplies blood to a volume of tissue becomes blocked by an [[embolus]], causing either no blood or at least not enough blood to reach the tissue. Hyperperfusion can be caused by [[inflammation]], producing [[hyperaemia|hyperemia]] of a body part. Malperfusion, also called poor perfusion, is any type of incorrect perfusion. There is no official or formal dividing line between hypoperfusion and [[ischemia]]; sometimes the latter term refers to zero perfusion, but often it refers to any hypoperfusion that is bad enough to cause [[necrosis]].{{citation needed|date=March 2021}}

==Measurement==
{{main|Perfusion scanning}}

In equations, the symbol Q is sometimes used to represent perfusion when referring to [[cardiac output]]. However, this terminology can be a source of confusion since both cardiac output and the symbol Q refer to [[volumetric flow rate|flow]] (volume per unit time, for example, L/min), whereas perfusion is measured as flow per unit tissue mass (mL/(min·g)).{{citation needed|date=March 2021}}

===Microspheres===
{{main|Microspheres}}
Microspheres that are labeled with [[radioactive isotopes]] have been widely used to measure perfusion since the 1960s. Radioactively labeled particles are injected into the test subject and a [[radiation detector]] measures radioactivity in tissues of interest.<ref name=Wagner>Studies of the Circulation with Radioactive Microspheres., Wagner et al, Invest. Radiol., 1969. 4(6): pp. 374–86.</ref> Microspheres are used in [[radionuclide angiography]], a method of diagnosing heart problems.

In the 1990s, methods for using [[fluorescent]] microspheres became a common substitute for radioactive particles.<ref name=OnlineGlenny>{{cite web|title=Fluorescent Microspheres|url=http://fmrc.pulmcc.washington.edu/DOCUMENTS/FMRCMAN99.pdf|publisher=[[Fluorescent Microsphere Resource Center]]|url-status=dead|archive-url=https://web.archive.org/web/20121002175850/http://fmrc.pulmcc.washington.edu/DOCUMENTS/FMRCMAN99.pdf|archive-date=2012-10-02}}</ref>

===Nuclear medicine===
{{main|Nuclear medicine}}
Perfusion of various tissues can be readily measured [[in vivo]] with nuclear medicine methods which are mainly [[positron emission tomography]] (PET) and [[single photon emission computed tomography]] (SPECT).{{citation needed|date=January 2014}} Various radiopharmaceuticals targeted at specific organs are also available, some of the most common are:{{citation needed|date=March 2021}}
* [[Technetium-99m|<sup>99m</sup>Tc]] labelled [[HMPAO]] and ECD for brain perfusion ([[Cerebral blood flow|rCBF]]) studied with SPECT
* [[Technetium-99m|<sup>99m</sup>Tc]] labelled [[Tetrofosmin]]  and [[Technetium (99mTc) sestamibi|Sestamibi]] for [[myocardial perfusion imaging]] with SPECT
* [[Xe-133|<sup>133</sup>Xe]]-gas for absolute quantification of brain perfusion ([[Cerebral blood flow|rCBF]]) with SPECT
* [[Oxygen-15#Oxygen-15|<sup>15</sup>O]]-labeled water for brain perfusion ([[Cerebral blood flow|rCBF]]) with PET (absolute quantification is possible when measuring arterial radioactivity concentration)
* [[Rubidium-82 chloride|<sup>82</sup>Rb-chloride]] for measuring myocardial perfusion with PET (absolute quantification is possible)

===Magnetic resonance imaging===
{{main|Magnetic resonance imaging}}
Two main categories of magnetic resonance imaging (MRI) techniques can be used to measure tissue perfusion [[in vivo]].
* The first is based on the use of an injected [[contrast agent]] that changes the [[magnetic susceptibility]] of blood and thereby the MR signal which is repeatedly measured during [[Bolus (medicine)|bolus]] passage.<ref>Huettel, S. A.; Song, A. W.; McCarthy, G. (2009), Functional Magnetic Resonance Imaging (2 ed.), Massachusetts: Sinauer, {{ISBN|978-0-87893-286-3}}</ref> 
* The other category is based on [[arterial spin labelling]] (ASL), where arterial blood is [[magnet]]ically tagged before it enters into the tissue being examined and the amount of labelling that is measured and compared to a control recording obtained without spin labelling.<ref>{{Cite journal|title = Applications of arterial spin labeled MRI in the brain|journal = Journal of Magnetic Resonance Imaging|date = 2012-05-01|issn = 1522-2586|pmc = 3326188|pmid = 22246782|pages = 1026–1037|volume = 35|issue = 5|doi = 10.1002/jmri.23581|first1 = John A.|last1 = Detre|first2 = Hengyi|last2 = Rao|first3 = Danny J. J.|last3 = Wang|first4 = Yu Fen|last4 = Chen|first5 = Ze|last5 = Wang}}</ref>

===Computed tomography (CT)===
{{main|Computed tomography}}
Brain perfusion (more correctly transit times) can be estimated with contrast-enhanced computed tomography.<ref>L. Axel. "Cerebral blood flow determination by rapid-sequence computed-tomography: theoretical analysis".  ''Radiology'' 137: 679–86, December 1980</ref>

===Thermal diffusion===
{{main|Molecular diffusion}}
Perfusion can be determined by measuring the total [[Molecular diffusion|thermal diffusion]] and then separating it into [[thermal conductivity]] and perfusion components.<ref>{{cite journal  |vauthors=Vajkoczy P, Roth H, Horn P, et al |title=Continuous monitoring of regional cerebral blood flow: experimental and clinical validation of a novel thermal diffusion microprobe |journal=Journal of Neurosurgery |volume=93 |issue=2 |pages=265–74 | date=August 2000 |pmid=10930012 |doi=10.3171/jns.2000.93.2.0265|s2cid=30375395 }}</ref> [[rCBF]] is usually measured continuously in time.  It is necessary to stop the measurement periodically to cool down and reassess the [[thermal conductivity]].{{citation needed|date=March 2021}}

==See also==
* {{annotated link|Reperfusion injury}}
* {{annotated link|Machine perfusion}}
* {{annotated link|Perfusionist}}
* {{annotated link|Myocardial perfusion imaging}}
* {{annotated link|Cerebral circulation#Imaging |rCBF}}
* {{annotated link|Cerebral edema}}
* [[Pressure ulcer]] — continuous external pressure impairs perfusion
* [[Cerebral perfusion pressure]]

==References==
{{reflist}}

==External links==
* [https://iperfusion.org/ International Perfusion Association]
* [https://web.archive.org/web/20150801033810/http://cardiacsurgeryportal.com/ Cardiac Surgery Portal]
* [https://perfusioneducation.com/blog/ Perfusion Education Portal]
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