Cerebral blood flow

Cerebral blood flow (CBF) is the supply of blood  to the brain over a  period of time. For adults, CBF is typically 750 milliliters per minute, or 15% of  cardiac output. This corresponds to an average perfusion of 50-54 milliliters of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the  metabolic requirements of the brain. Too much blood (clinical state of  normal homeostatic response to hyperemia) increases intracranial pressure (ICP), which can compress and damage delicate brain tissue. .. Low blood flow (ischemia) occurs when blood flow to the brain falls below 18-20 ml per 100 g / min, and tissue death occurs when blood flow falls below 8-10 ml per 100 g / min. increase. The biochemical cascade, known as the ischemic cascade, is triggered in brain tissue when the tissue becomes ischemic, which can lead to brain cell damage  and death. Physicians should take steps to maintain proper CBF for patients with conditions such as shock, stroke, cerebral edema, and traumatic brain injury.

 

Cerebral blood flow is determined by many factors, including: B. Blood viscosity, vasodilators, and  net pressure of blood flow to the brain. This is known as cerebral perfusion pressure, which is determined by the body's blood pressure. Cerebral perfusion pressure (CPP) is defined as  mean arterial pressure (MAP) minus  intracranial pressure (ICP). For the average person, it should be at least 50mmHg. Intracranial pressure should not exceed 15 mm Hg (20 mm Hg ICP is considered to be intracranial hypertension). Cerebral blood vessels can change blood flow  through them by changing their diameter in a process called cerebral autoregulation. When systemic blood pressure rises, it contracts, and  when it falls, it expands.  Arterioles also contract and dilate in response to different chemical concentrations. For example, it expands when the carbon dioxide level in the blood is high, and contracts when the carbon dioxide level is low. Assume a person with a arterial partial pressure  of 40 mmHg (normal range 38-42 mmHg) and a CBF of 50 ml per 100 g / min. If  PaCO2 is reduced to 30 mmHg, this corresponds to a 10 mmHg reduction from the initial PaCO2 value. As a result, for every 1 mmHg reduction in PaCO2, the CBF is reduced by 1 mL per 100 g / min, resulting in a new CBF of 40 mL per 100 g / min of brain tissue. In fact, for every 1 mmHg increase or decrease in PaCO2 in the 20-60 mmHg range, there is a corresponding CBF change of approximately 1-2 mL / 100 g / min, or 2-5% of CBF, in the same direction. [14] Therefore, small changes in respiratory patterns can cause large changes in global CBF, especially from PaCO2 fluctuations.