Week 6 - Brain blood flow and exercise Flashcards
Why is blood flow to and within the brain vital?
Its vital for survival and functional consequences such as performance, cognitive function, and preventing disease/conditions (stroke, dementia).
What % of body mass is the brain? What % of total cardiac output does it demand?
Brain only 2-3% of body mass, yet demands 20% of total cardiac output.
Why is habitual exercise important for brain blood flow?
Habitual exercise offsets the natural age-related decline in brain blood flow.
Two factors that reduce size of brain (and consequent blood flow)
1) Ageing
2) Inactivity
What does Near-Infrared Spectroscopy (NIRS) measure?
The balance of oxygen supply and oxygen demand directly at a capillary level in cerebral cortical tissue.
Gives us a measure of brain activation - neurovascular coupling.
What method of assessing the brain is suited to dynamic exercise?
Transcranial Doppler
- measures blood velocity as an index of flow
5 factors that regulate blood flow.
1) Metabolism
2) Blood pressure
3) Neurogenic (Cerebral SNA)
4) Chemical (key factor - oxygen and carbon dioxide values in blood)
5) Cardiac output (key factor)
How can we explain why athletes faint after a long exercise bout or a maximal bout such as a deadlift?
During exercise, blood vessels are dilated to deliver blood to the muscles.
When exercise stops, we get a sudden drop in blood pressure but blood vessels are still dilated to the muscle, so we get a decline in BBF. This can result in fainting.
How does hyperventilation (during a deadlift) influence BBF?
It will decrease BBF because hyperventilating reduces arterial PCO2 - this can result in fainting.
What is the relationship between brain blood flow and arterial partial pressure of carbon dioxide (PaCO2)?
Brain blood flow increases as PaCO2 increases (not linear)
What is the relationship between brain blood flow and exercise intensity?
Inverted U response
- Once you go over the anaerobic threshold you start to hyperventilate (due to H+ production) so we reduce C02 which results in reduced BBF.
What happens to BBF when you hold PetCO2 (partial pressure of end-tidal carbon dioxide) constant as exercise intensity increases?
BBF continues to rise
Is the pattern of BBF the same for all exercise modalities?
NO - they appear to be different between exercise modes
What are exercise-induced changes in BBF dependent on?
1) The exercise modality (run vs cycle)
2) Exercise protocol used (HIIT/continuous)
3) Fitness level (fitter individuals get increase in BBF at higher intensities)
What acute events and chronic clinical conditions are associated with impaired BBF?
Acute events: faint, stroke
Chronic clinical conditions: hypertension, dementia, concussion
