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The brain is a complex organ that requires an adequate blood supply to function normally. Blood flow to the brain is called perfusion. Cerebral Perfusion Pressure (CCP) is typically the force of the pressure in the arteries leading to the brain, blood pressure in the jugular veins, and the Intracranial Pressure (ICP) inside the head. The mean arterial pressure can push blood into the head, while the ICP lowers the CCP. Blood vessels in the brain called arterioles are usually able to widen in order to lower pressure, while they can constrict to raise it.
Through autoregulation, arteries in the brain can widen and constrict to keep the pressure in the brain relatively constant. Changing blood pressure in the body, therefore, typically does not have much of an effect. If the cerebral perfusion pressure is not regulated in the normal way, this can result in pressure-passive flow. There can be inadequate blood pressure in the brain, resulting in oxygen-starved cells causing a condition called ischemia.
Too much pressure in the brain can trigger neurological damage and may cause parts of the organ to herniate. Cerebral perfusion pressure typically needs to stay in a narrow range for blood flow and neurological activity to be healthy. It is often compromised after a head injury and physicians can monitor CPP by tracking jugular venous pressure and oxygen saturation. If blood flow to the brain is too low, this saturation value will lower because more oxygen is drawn from what little blood supply is available.
Cerebral perfusion pressure can also be monitored by assessing the metabolic activity of brain cells. Positron Emission Tomography (PET) scans are often used to image these areas and compare this activity versus the CPP. A catheter is sometimes inserted into the brain to assess the metabolic state of an area. This method is typically invasive and the presence of the catheter can change the physical state of the areas being measured.
Sometimes the symptoms of a patient can be used to determine cerebral perfusion pressure. Physicians can estimate the ICP based on whether someone is experiencing confusion or drowsiness, for example. The mean arterial pressure can be used with the resulting numerical estimation to determine the CPP. Outcomes for cranial injury victims are often predicted by monitoring cerebral perfusion pressure as well, because the blood flow and pressures in the head usually correlate with brain function and its ability to heal.