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=
𝑆𝐵𝑃+2𝐷𝐵𝑃
3

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

4. Autoregulation
• Cerebral autoregulation refers to the physiological mechanisms that
maintain blood flow at an appropriate level during changes in blood
pressure.
1. Metabolic regulation
2. Myogenic regulation
3. 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:
1. Increase CO2
2. Increase H ion “Lactic acidosis”
3. Increase O2 consumption
4. 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
CerebralBloodFlow
HTN
Normal

10. Thank you
Presented By;
Ahmed Mahmood