Cerebrovascular

Question 1

Why is cerebral circulation important?

Answer 1

-vascular conductance to working muscles decreases dramatically during exercise
-blood pressure must be maintained to perfume the brain
-brain is positioned at the top of circulatory system under the force of gravity, therefore, pressure maintenance during exercise is extremely important

Question 2

How much global blood flow do the internal carotid arteries (ICA’S) account for

Answer 2

~70%

Question 3

How much global cerebral blood flow do the vertebral arteries account for

Answer 3

~30%

Question 4

Describe the circle of Willis

Answer 4

Internal carotid artery on the upper left
Middle cerebral artery on the upper right
Basilar artery on the bottom near occipital lobe

Question 5

How can we measure cerebral blood flow

Answer 5

TRANSCRANIAL DOPPLER ULTRASOUND

Question 6

What is the Doppler effect

Answer 6

Describes the change in frequency of wave in relation to an observer who is moving relative to the source of the wave
(Think of an ambulance thats far away from you, the frequency and pitch are gonna be lower rather than if it was close to you)

Question 7

What is the transcranial Doppler ultrasound

Answer 7

-used to insonate the vessels
-lower frequency probe to get though thick bone
-the ultrasound is reflected with a positive or negative frequency shift (blood going away or towards the probe will show up as different colours )

Question 8

What are some applications of measuring cerebral blood flow

Answer 8

-detecting severe intracranial stenosis
-evaluating cerebral malformations
-assessing cerebrovascular dysfunction
-research tool for beat-by-beat cerebral blood velocity

Question 9

What is a major disadvantage of the transcranial Doppler

Answer 9

Measures blood VELOCITY not cerebral blood flow

-assumes that the blood vessel does not change diameter (which likely isn’t the case)

Therefore during exercise TCD may not be a valid measurement of CBF

Question 10

What DOES measure both blood velocity and blood vessel diameter?

Answer 10

Duplex ultrasound

Question 11

What are some advantages of the duplex ultrasound

Answer 11

Measures both blood vessel diameter and blood velocity (TCD only measures velocity)

Beat-by-beat measurements

Question 12

What are some DISADVANTAGES of the duplex ultrasound

Answer 12

-user dependent
-requires extensive training (100’s of hours)
-interventions that involve movement make measurements difficult

Question 13

What is neurovascular coupling

Answer 13

Describes the relationship between local neuronal activity and subsequent changes in cerebral blood flow

Question 14

Why does CBF go down when nearing maximal exercise?

Answer 14

Because exercise causes hyperventilation which then makes the body hypocapnic. This then causes a decrease in flow /perfusion pressure, which therefore reduces the venous return