Cerebral blood flow
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2008-05-22T07:03:39Z
Rjwilmsi
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[[WP:AWB/T|Typo]]/[[Template:Citation|date]] fixes, Replaced: milllitres → millitres using [[Project:AutoWikiBrowser|AWB]]
'''Cerebral blood flow''', or '''CBF''', is the blood supply to the [[brain]] in a given time.<ref name="Tolias">Tolias C and Sgouros S. 2006. [http://www.emedicine.com/med/topic3216.htm "Initial Evaluation and Management of CNS Injury."] Emedicine.com. Accessed [[January 4]], [[2007]].</ref> In an adult, CBF is 750 mls/min or 15% of the cardiac output. On a weight basis, this is 50 to 54 millilitres/100grams/minute.<ref name="Orlando Regional Healthcare">Orlando Regional Healthcare, Education and Development. 2004. [http://www.orlandoregional.org/pdf%20folder/overview%20adult%20brain%20injury.pdf "Overview of Adult Traumatic Brain Injuries."] Accessed [[2008-01-16]].</ref><ref name="shep">Shepherd S. 2004. [http://www.emedicine.com/med/topic2820.htm "Head Trauma."] Emedicine.com. Shepherd S. 2004. [http://www.emedicine.com/med/topic2820.htm "Head Trauma."] Emedicine.com. Accessed [[January 4]], [[2007]]. </ref><ref name="Walters">Walters, FJM. 1998. [http://www.nda.ox.ac.uk/wfsa/html/u08/u08_013.htm "Intracranial Pressure and Cerebral Blood Flow."] Physiology. Issue 8, Article 4. Accessed [[January 4]], [[2007]]. </ref>
CBF is equal to the [[cerebral perfusion pressure]] (CPP) divided by the cerebrovascular resistance (CVR):<ref>AnaesthesiaUK. 2007. [http://www.anaesthesiauk.com/article.aspx?articleid=100754 Cerebral Blood Flow (CBF)]. Accessed [[2007-10-16]].</ref>
:CBF = CPP / CVR
Control of CBF is considered in terms of the factors affecting CPP and the factors affecting CVR.
Control of the CVR is by four major mechanisms:
# [[Metabolic]] control (or 'metabolic autoregulation')
# Pressure [[autoregulation]]
# Chemical control (by arterial pCO2 and pO2)
# [[Neural]] control
CBF is tightly regulated to meet the brain's [[metabolism|metabolic]] demands, and on the average must be maintained at a flow of 50 milliliters of blood per 100 grams of brain tissue per minute in adult humans.<ref name="Orlando Regional Healthcare"/><ref name="sgo">Singh J and Stock A. 2006. [http://www.emedicine.com/ped/topic929.htm "Head Trauma."] Emedicine.com. Accessed [[January 4]], [[2007]].</ref> It is important to maintain CBF within narrow limits because too much blood can raise [[intracranial pressure]] (ICP), which can compress and damage delicate brain tissue, and too little blood causes [[ischemia]], or inadequate blood supply. Ischemia results if blood flow to the brain is below 18 to 20 ml per 100 g per minute, and tissue death occurs if flow dips below 8 to 10 ml per 100 g per minute. In brain tissue, a [[biochemical cascade]] known as the [[ischemic cascade]] is triggered when the tissue becomes ischemic, potentially resulting in damage to and death of [[neuron|brain cells]]. Medical professionals must take steps to maintain proper CBF in patients with conditions like [[Shock (medical)|shock]], [[stroke]], and [[traumatic brain injury]]. Cerebral blood flow in excess of 55 to 60 ml per 100 g per minute, called [[hyperemia]], is more than the brain needs and can contribute to an increase in intracranial pressure.
Cerebral blood flow is determined by a number of factors, such as [[viscosity]] of blood, how dilated [[blood vessel]]s are, and the net pressure of the flow of blood into the brain, known as [[cerebral perfusion pressure]], which is determined by the body's [[blood pressure]] and intracranial pressure. Cerebral blood vessels are able to change the flow of blood through them by altering their diameters in a process called [[autoregulation]]; they constrict when systemic blood pressure is raised and dilate when it is lowered<ref name="Kandel">Kandel E.R., Schwartz, J.H., Jessell, T.M. 2000. Principles of Neural Science, 4th ed., McGraw-Hill, New York. p.1305</ref> Arterioles also constrict and dilate in response to different chemical concentrations. For example, they dilate in response to higher levels of [[carbon dioxide]] in the blood.<ref name="Kandel"/>
[[Functional magnetic resonance imaging]] and [[positron emission tomography]] are [[neuroimaging]] techniques that can both be used to measure CBF. These techniques are also used to measure regional CBF (rCBF) within a specific brain region.
==See also==
*[[Cerebral perfusion pressure]]
*[[Cerebral circulation]]
*[[Perfusion Scanning]]
==References==
<references />
[[Category:Neurology]]
[[Category:cardiovascular system]]