View source for Cerebral blood flow

'''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 typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per 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 tightly regulated to meet the brain's [[metabolism|metabolic]] demands.<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> Too much blood (a condition known as [[hyperemia]]) can raise [[intracranial pressure]] (ICP), which can compress and damage delicate brain tissue. Too little blood flow ([[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 who have conditions like [[Shock (circulatory)|shock]], [[stroke]], and [[traumatic brain injury]].

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"/>

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. CVR is controlled by four major mechanisms:
# [[Metabolic]] control (or 'metabolic autoregulation')
# Pressure [[autoregulation]]
# Chemical control (by arterial pCO<sub>2</sub> and pO<sub>2</sub>)
# [[Neural]] control 

[[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]]
[[Category:2Fix]]