Autoregulation of cerebral blood flow

Autoregulation of cerebral blood flow

1. Autoregulation of cerebral blood flow Active Hyperemia Phenomenon By Ahmed Mahmood

2. Brain 1/50 of body weight in adult 1/6 = about 15% of cardiac output 1/5 of oxygen consumption Cerebral blood flow: 50-60 ml/100 g of brain tissue/min Cerebral perfusion pressure , or  CPP , is the net pressure gradient causing cerebral blood flow to the brain (brain perfusion). CPP=MAP-ICP or JVP (whichever is higher) MAP  

3. Cerebral blood flow relation to MAP . Mean Arterial Pressure Cerebral Blood Flow Autoregulation

4. Autoregulation Cerebral autoregulation refers to the physiological mechanisms that maintain blood flow at an appropriate level during changes in blood pressure. Metabolic regulation Myogenic regulation Neurogenic regulation

5. Metabolic Metabolic regulation is driven by the balance between cerebral metabolism (demand) and oxygen delivery through cerebral blood flow (supply) and acts by means of a vasoactive substance. In principle, this is a negative feedback control system that seeks to balance cerebral blood flow to its demand. Increase blood flow in response to: Increase CO2 Increase H ion “Lactic acidosis” Increase O2 consumption Increase Temperature

6. Myogenic regulation The effect of transmural blood pressure changes are directly detected by the vascular smooth muscle in arterioles, probably via a stress sensing mechanism. Then, the calibers are adjusted accordingly to keep blood flow constant.

7. Neurogenic regulation The vascular smooth muscle in the arterioles are controlled via: sympathetic innervation, receiving the input from the appropriate brainstem autonomous control center. Nitric oxide released by parasympathetic fibers may also play a role. Astrocytes control of the cerebral blood flow according to the local brain activity

8. Neurogenic regulation Astrocytes effect on CBF

9. Cerebral Blood flow in Hypertension It’s beneficial to keep the baseline BP high in patient with ischemic stroke Mean Arterial Pressure Cerebral Blood Flow HTN Normal

10. Thank you Presented By; Ahmed Mahmood