Brain Injury

Question 1

True or False: Brain can withstand long periods of ischaemia

Answer 1

False

Question 2

What is the primary regulator of blood flow in the brain?

Answer 2

CO2 as it is a potent vasodilator

Question 3

What is the formula for cerebral blood flow (CBF)?

Answer 3

Cerebral perfusion pressure (CPP)/ Cerebral vascular resistance (CVR)

Question 4

What is CBF affected by?

Answer 4

PaO2, PaCO2, pH, BP, cardiac function, blood viscosity

Question 5

What is CBF autoregulation?

Answer 5

brain’s intrinsic ability to maintain a constant CBF despite marked changes in systemic BP through vessel constriction and dilation.

Question 6

What does CBF autoregulation maintain?

Answer 6

mean arterial pressure (MAP) = 60-140 mmHg

Question 7

What is Formula 1 for calculating MAP?

Answer 7

MAP = (2XDP +SP)/3 
DP = diastolic pressure
SP = systolic pressure

Question 8

What is Formula 2 for calculating MAP?

Answer 8

MAP = DP + 1/3PP
DP = diastolic pressure
PP = pulse pressure, the recoil of the artery following the heart's beat

Question 9

How does an increase in CO2 affect CBF?

Answer 9

Increased CO2 = increased PaCO2 = acidosis = vasodilation = increase CBF

Question 10

How does a decrease in CO2 affect CBF?

Answer 10

Decreased CO2 = decreased PaCO2 = alkalosis = vasoconstriction = decrease CBF

Question 11

How does a decrease in O2 affect CBF?

Answer 11

Decreased O2 = decreased PaO2 = acidosis = vasodilation = increase CBF

Question 12

How do H+ ions affect CBF?

Answer 12

• CO2 + H2O = carbonic acid = dissociation of H+ ions = acidosis
• H+ concentration can also be increased by the production of lactic acid (product of cell metabolism)
• pH changes = decreased pH = acidosis = vasodilation = increased CBF and vice versa (outcome of H+, CO2 and O2 changes in the blood)

Question 13

What triggers physiological mechanisms regulating CBF?

Answer 13

Changes in systemic and pial arterial pressure
Changes in O2 (reduction, ie: asphyxia) and CO2 levels (increase, asphyxia)
Primary decrease/restriction through arteries in CBF ie: absence of adequate blood supply due to clot.
Increase in cerebral blood volume (bleeding into brain tissue)

Question 14

Where does CSF lie and where is it produced?

Answer 14

Lies in the ventricles of the brain

Produced in the choroid plexus

Question 15

What is the pathway of flow for CSF?

Answer 15

made in one of the lateral ventricles (choroid plexus) and moves through the third and fourth, to go to the spinal cord.
CSF goes into the subarachnoid space and is absorbed by the subarachnoid villi to return to circulation