Topic 4 - CBF regulation

Question 1

what are the stats of the brain (weight, O2 consumption, energy storage)

Answer 1

~2% of body size
consumes ~20% resting O2 content
brain doesn’t store energy (lose consciousness in 8-10 sec if blood flow is stopped)

Question 2

what are the effects of reduced glucose and O2 to the brain

Answer 2

reduced glucose = mental confusion, dizziness, unconsciousness (severe)

reduced O2 = weakening, permanent damage/death of brain cells

Question 3

what occurs with disruptions to brain blood flow

Answer 3

pass out (benefit = BP stabilised across the body)

stroke
- ischemic (reduced blood flow to an area - death of neurons downstream)
- hemorrhagic (weakening of cell wall and ruptures - causes squished neurons)

Question 4

what is the doppler ultrasound

Answer 4

measures cerebral blood flow
very high temporal resolution
works by measuring velocity changes (changes in pitch with moving sound waves)

Question 5

why is the angle of insonation important

Answer 5

want to have as close to 0 as possible (in line with the vessel) to measure velocity

Question 6

what are differences in velocity caused by

Answer 6

variation depends on the vessel
bigger vessels = higher velocity
slower with age = less blood to the brain (can prevent with exercise)

Question 7

what are the 3 main CBF regulation mechanisms

Answer 7

BP
neural activity
CO2 (brain is way more sensitive than the rest of the body)

Question 8

what is the relationship between blood flow and BP

Answer 8

decrease in blood flow = decrease in BP
(NOT lassens curve with a plateau)
- need to have concerns about effect of BP

Question 9

what types of changes can the brain adjust for

Answer 9

slower changes
- brain can’t adapt quick enough for rapid changes

brain wants to protect itself from over perfusion

Question 10

how does the brain deal with high and low frequency osscilations

Answer 10

high frequency (cardiac cycle)
- sympathetic contorl to buffer ahead of time

lower frequency
- sympathetic (0.1 Hz)
- myogenic - calcium channels and smooth muscle tone (0.05 Hz)
both extensively filtered

Question 11

when does the brain adapt to pressure changes

Answer 11

before the change in pressure
- phase lead (x-axis) (changing before the body) is usually more robust than the gain
- gain measures (y-axis)

Question 12

what is the relationship between activation and blood flow and vasodilation

Answer 12

different activities = different levels of activation

more activity = more nutrient delivery to maintain function

more blood flowing = increased friction on blood vessel = higher shear stress = endothelium releases endothelium nitric oxide (dilator)

sends signals to propagate dilation to get more blood to the working area

Question 13

what are the potential underlying mechanisms for neurovascular coupling

Answer 13

• singular onset signal responsible for the time delay between signal and initial increase in CBF (likely at pericytes)
• signal propagates up the vascular tree and alters CBF to meet metabolic demand
• increased metabolism = release of metabolic byproducts (CO2, NO2, acids) = vasodilatory

Question 14

what happens to metabolic demands and CBF over time

Answer 14

balance reached between the metabolic demands of the task and level of CBF

Question 15

what is the relationship between neuronal activity and glucose/O2

Answer 15

increases in activity must be accompanied by rapid (seconds) localised elevations in O2 and glucose to avert the development of ischemic conditions

brain makes rapid dynamic changes not based on CO2

Question 16

what is the normal level of CO2 in the brain

Answer 16

40 mmHg

Question 17

what happens to CBF when the brain goes above and below 40 mmHg CO2

Answer 17

above 40 (holding breath) = increase in brain blood flow (higher response)

below 40 (over breathing) = decrease in brain blood flow

consistent across both sides of the brain

Question 18

what measure is a fairly good index of arterial CO2 levels

Answer 18

end tidal CO2