Week 13 Flashcards
There are 5 main components to the Circle of Willis:
- anterior cerebral artery
- anterior communicating artery
- internal carotid arteries
- posterior cerebral artery
- posterior communicating artery
The circle of willis is…
a junction of several important arteries at the bottom part of the brain.
Originally cerebral BF was measured using inert ____
tracers
- Method is based on Fick principle: arterio-venous difference of tracer is proportional to volume of blood flow through brain
Limitations of tracers
- Poor temporal resolution
- Only global measure of blood flow
- Arterial lines necessary
- Value of cerebral oxygenation must be assumed
- Venous outflow from brain may not be symmetrical
How is blood flow measured now?
Transcranial Doppler (TCD): Tool for examining cerebrovascular function (relatively low-cost, easy to use, non-invasive, high temporal resolution).
Insonation is possible through thinner regions of the skull, termed “_____” windows, making it feasible to measure static and dynamic blood velocities within the major cerebral arteries through the transcranial doppler (TCD)
acoustic
The transcranial doppler (TCD) measures cerebral blood flow _____
velocity
Key regulators of cerebral blood flow include:
- cerebral metabolism (neurovascular coupling)
- partial pressure of arterial Co2 (cerebrovascular reactivity)
- Mean arterial pressure (cerebral autoregulation)
Cerebral BF regulator: Cerebral metabolism (neurovascular coupling) …
Neuromuscular coupling can be demonstrated when measuring posterior cerebral artery velocity during activities such as reading
- higher the activity, more blood flow required, brain adapts to it
Cerebral BF regulator: Partial pressure of arterial Co2 (cerebrovascular reactivity)
Co2 increases cerebral blood flow (and Co2 decrease, decreases BF to brain)
Decrease in PaCo2 (hypoxia) causes cerebral vasodilation leading to increase in ____ (i.e. opposite effect of CO2)
cerebral BF
However, hypoxia leads to hyperventilation (when there is not enough O2 and we try to breathe to quickly and too deeply), which causes hypocapnia (fall in Co2), leading to ______ cerebral blood flow
decreased
Cerebral BF regulator: Mean arterial pressure (cerebral autoregulation)
Dynamic cerebral autoregulation = ability of cerebrovasculature to resist acute changes in perfusion pressure (due to changes in BP) over a short time course of less than 5 seconds
Assessment of cerebral autoregulation:
- Transfer function analysis
- Postural alterations
- Valsalva manoeuvre
- The Oxford technique
- Suprasystolic thigh cuffs
Changes in BP used to assess response of cerebral BF (cerebral autoregulation)
Thigh cuff deflation:
- Thigh cuffs are inflated to suprasystolic (above systolic) pressures for >2min
- Rapid deflation of cuffs causes transient hypotension
- Rate at which cerebrovascular resistance changes in response to BP is measured
Name the key regulators of cerebral blood flow and describe how each affects cerebral blood flow
Co2 / cerebrovascular reactivity
- Increase in cerebral blood flow with increase in CO2
Metabolism / neurovascular coupling
- Increase in cerebral blood flow with increase in metabolism
Cerebral perfusion pressure / MAP / cerebral autoregulation
- Increase in cerebral blood flow with increase in BP
Co2 / cerebrovascular reactivity causes
- Vasodilation of downstream arterioles with increase in Co2
- Increase in cerebral blood flow with increase in CO2
Metabolism / neurovascular coupling causes
- Increase in cerebral blood flow with increase in metabolism
Cerebral perfusion pressure / MAP / cerebral autoregulation causes
Increase in cerebral blood flow with increase in BP
Study Indicates that regional and global _____ in cerebral BF occur during exercise
increases
Increases in exercise intensity up to about __% Vo2max produce elevations in cerebral blood flow
60%
During heavy exercise to exhaustion, changes in cerebral blood flow are not matched with brain neuronal activity and metabolism. Instead, metabolism is maintained by increases in uptake of ___ ____ and _____.
lactate glucose, oxygen
Brys et al. (2003) reported that the VARIABILITY of cerebral blood flow
remains _____ during progressive elevations in exercise intensity
despite an increased variability in blood pressure.
stable
With healthy human ageing, there is a progressive decline in CBF in the order of ____% from the age of 30 to 70 yr
28-50%
Ageing is associated with global cerebral ____
atrophy
Ageing: Decreases in CBF reflect global _____ in cerebral perfusion, without disturbance of regional perfusion of O2 consumption
decrease
Ageing: studies showed rapid ____ in cerebral BF during childhood with gradual decline across remaining age span
- _______ in cerebral O2 consumption with ageing
fall, decrease
Only artery that doesn’t change much with ageing is the only one not supplying the brain–>
external carotid artery
According to Xing et al., advancing age is associated with:
- Imparied baroreflex sensitivity at rest
- Impaired cerebral autoregulation at rest
How can habit exercise throughout the lifespan affect the decline in CBF with age?
Habitual physical activity may offset the normal age-related declines in cerebral blood flow.
Two key regulators of cerebral blood flow (CBF) are partial pressure of arterial ________ and __________ (and thus cerebral perfusion pressure)
Co2 (PaCo2), mean arterial pressure
Increases in exercise intensity up to 60% of max O2 uptake produce elevations in CBF, after which CBF decreases toward baseline values despite further _____ in exercise intensity and brain metabolism
increases
A rapid fall in cerebral blood flow occurs during ______ with more gradual decline across remaining age span. However, habitual physical activity may offset the normal age-related declines in cerebral blood flow.
childhood
Which of the following is not a key regulator of cerebral blood flow? a) PaCO2 b) Cerebral perfusion pressure c) Cerebral metabolism d) Acetylcholine
d) Acetylcholine
Which of the following statements best describes the
influence of exercise on cerebral blood flow (CBF)?
a) Increases in exercise intensity up to 60% VO2max
produce elevations in CBF, after which CBF decreases
towards baseline values despite further increases in
exercise intensity and brain metabolism
b) Cerebral blood flow increases in direct proportion to
exercise intensity, with the greatest levels of CBF evident
during maximal exercise.
c) Cerebral blood flow remains stable at all intensities of
exercise.
d) Cerebral blood flow declines as exercise intensity
increases in order to distribute more blood to the
working muscles.
a) Increases in exercise intensity up to 60% VO2max
produce elevations in CBF, after which CBF decreases
towards baseline values despite further increases in
exercise intensity and brain metabolism
What happens to resting cerebral blood flow and cerebral oxygenation (expressed relative to brain mass) across the lifespan?
a) Cerebral blood flow and oxygenation are stable through the
lifespan and only decline when an individual is suffering from
disease.
b) Cerebral blood flow and cerebral oxygenation are at their greatest during childhood, but they rapidly decline until puberty, after which there is a more gradual decline across the remaining age span.
c) Cerebral blood flow and cerebral oxygenation increase with
advancing age and increases in body mass.
d) Changes in cerebral blood flow and cerebral oxygenation
across the lifespan follow an inverted-U pattern in which they
are highest during childhood and old age.
b) Cerebral blood flow and cerebral oxygenation are at their greatest during childhood, but they rapidly decline until puberty, after which there is a more gradual decline across the remaining age span.
