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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]]. 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 and constrict to lower levels of carbon dioxide.<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>
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