CH. ???? Flashcards
main cardiovascular responses to acute exercise
- > blood flow redistribution
- > cardiovascular drift
- > competition for blood supply
- > blood oxygen content
what happens when blood flow is redistributed during exercise
- > increased cardiac output which leads to increased available blood flow
*must redirect BF to areas w/greatest metabolic needs
- > sympathetic vasoconstriction shunts blood away from less active regions (via splanchnic circulation and kidneys)
- > local vasodilation permits additional BF in exercising muscles
*local VD triggered by metabolic and endothelial product
- > as temp increases, skin VD also increases
*decreased symp VC, inc symp VD permits heat loss through the skin
cardiovascular drift
upward drift of HR over time
- > associated with increased core temp and dehydration
as SV drifts down
- > skin BF increases
- > plasma vol decreases (sweating)
- > venous return/preload decreases
HR drifts increase to compensate (Q in maintained)
describe/explain the competition for blood supply
exercise and others demand blood flow as such they must compete for a set Q
- > multiple demands may decrease muscle blood flow
exercising (muscle) + eating
exercising (muscle) + nothing
how does blood content change during exercise
(a-v) O2 difference
- > 1ml O2 / 100mL of blood
resting: ~6mL O2/ 100ml blood
active: ~16-17mL O2/ 100mL of blood
Mixed venous O2 >or equal 4mL O2 /100mL blood
- > venous O2 from active muscle ~0ml
- > venous O2 from inactive muscles > active muscles
- > increases mixed venous O2 content
central regulation of cardiovascular responses
What stimulates rapid change in HR, Q, and BP during exercise
- > precede metabolite buildup in muscle
- > HR increases within 1s of the onset of exercise
Central Command
- > higher brain centres
- > co-activates motor and cardiovascular centres
what is the body’s first priority during the onset of exercise
- > maintenance of BP
cardiovascular responses to exercise are complex, fast, and finely tuned
ventilation during exercise
immediate increase in ventilation during exercise
- > begins before muscle contractions
- > anticipatory response from central command
gradual second phase of increase in vent.
- > driven by chem changes in arterial blood; inc CO2, H+ sensed by chemoreceptors; right arterial stretch receptors
ventilation increase in proportional to metabolic needs of muscle
- > at low exercise intensity: only tidal volume increases
- > at high exercise intensity: rate also increases
ventilation recovery after exercise delayed
- > recovery takes several minutes
- > may be regulated by blood pH, PCO2 and tempp
why can the valsalva maneuver be potentially dangerous
if you have high blood pressure/ are exercising hard, it will increase intra-abdominal and intra-thorasic pressure
these high pressures can colapse the great veins - > decreased venous return - > decreased Q - > decreased arterial BP
how is ventilation and energy metabolism related
ventilation matches metabolic rate
- ventilatory equivalent for O2*
- > Ve/VO2 (L air breathed / L O2 consumed/min)
- > index of how well control of breathing matched to body’s demand for oxygen
- Ventilatory threshold*
- > point where L air breathed > L O2 consumed
- > associated with lactate threshold and increased PCO2
estimating lactate threshold
- ventilatory threshold as a surrogate measure?*
- > excess lactic acid+ sodium bicarbonate
- > result: excess Na lactate, H2O and Co2
- > lactic acid, CO2 accumulate simultaneously
refined to better estimate lactate threshold
- > anaerobic threshold
- > monito both VE/VO2 and VE/VCO2
how can ventilation create limitations to performance
ventilation normally does not limit performance
- > respiratory muscles account for 10% of VO2, 15% of Q during heavy exercise
- > respiratory muscles are very fatigue resistant
- > airway resistance and gas diffusion normally not limiting factors at sea level
- > restrictive or obstructive respiratory disorders can be limitint
exception: elite endurance-trained athletes exercising at high intensity
- > ventilation may be limiting
- > ventialtion-perfusion mismatch
- > exercise induced arterial hypoxia (EIAH)
