CIRCULATORY RESPONSE TO EXERCISE
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Transcript CIRCULATORY RESPONSE TO EXERCISE
CIRCULATORY RESPONSE TO
EXERCISE
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The Circulatory System
• Heart
– Pumps blood
• Arteries and arterioles
– Carry blood away from the heart
• Capillaries
– Exchange of nutrients with tissues
• Veins and venules
– Carry blood toward the heart
Acute cardiovascular (circulatory
system) responses to exercise
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heart rate
stroke volume
cardiac output
blood pressure
blood flow
blood plasma volume
Circulatory Responses to Exercise
• Heart rate and blood pressure
Depend on:
– Type, intensity, and duration of exercise
– Environmental condition
– Emotional influence
Changes in Cardiac Output during Exercise
• CO increases during exercise in direct
proportion to metabolic rate required to
perform the exercise task.
• due to an increase in HR & SV
[CO = SV x HR]
• BUT: In untrained & moderately trained, at
work rates >40% - 60% VO2max the increase in
CO is from increase in heart rate only.
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• As work rate increases, the following also
increase:
1. Arteriovenous O2 difference.
• The extent to which O2 is extracted from the
blood as it passes through the body
• Calculated as the difference between the
oxygen content of arterial blood and right
atrial blood
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• Arteriovenous difference increases with
increasing exercise intensity:
more oxygen being extracted from
the blood and used for oxidative
production of ATP by skeletal
muscle
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2. Blood pressure
As work rate increases, BP also increases (as more
blood is pumped to working muscle from the
heart):
Mean arterial pressure (MAP)
– Average pressure in the arteries
• Maximal CO tends to decrease in linear fashion
after 30years of age.
• This is due to decrease in heart rate with age.
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Redistribution of Blood flow during Exercise
7/18/2015
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Redistribution of Blood flow during Exercise
• During maximal exercise: 80% - 85% of total
CO goes to contracting muscles.
necessary to meet the huge increase in
muscle oxygen requirements during intense
exercise.
• Increase to muscles is due to redistribution of
blood flow from inactive organs to the
contracting skeletal muscles.
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• Vasodilation of arterioles feeding
the contracting skeletal muscles:
reduces the vascular resistance
and therefore increases blood flow.
• Also, recruitment of capillaries in skeletal
muscle:
At rest only 50% - 80% are open
During intense exercise almost all open
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Emotional Influence
•Submaximal exercise in an emotionally charged
atmosphere = higher heart rates & blood
pressure.
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Transition From Rest Exercise
Recovery
• Onset of exercise = Rapid increase in HR, SV, CO
• If the work rate is constant & below the lactate
threshold = a steady state plateau is reached (in
HR, SV, CO)
• Recovery depends on:
– Duration and intensity of exercise
– Training state of subject
Circulatory Responses to Exercise-Incremental
Exercise
• HR and CO increase in direct proportion to
oxygen uptake.
• This ensures that there is enough O2 available
for ATP synthesis.
• Both then reach a plateau at about 100%
VO2max
• This point represents a maximal ceiling for O2
transport to exercising muscles
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• The elevation in mean arterial blood pressure
during exercise is due to increase in systolic
pressure.
• Diastolic pressure remains fairly constant
during incremental work
• Increase in exercise intensity = increase in
both HR and SBP
=increases the work load placed on the heart.
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Recovery from exercise
• Recovery from short
term, low intensity
exercise is generally
rapid
• Recovery speed varies
from individual to
individual:
Trained: recover more
quickly & easily than
untrained.
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Circulatory Responses to Intermittent
Exercise
• Discontinuous exercise (interval training,
stop/start):
Recovery of HR & BP between bouts depends
on:
1. Level of fitness
2. Environmental conditions
(temperature, humidity)
3. Duration and intensity of exercise.
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Circulatory Responses to Intermittent
Exercise
• Light exercise in a cool environment =
generally complete recovery between bouts.
• Intense exercise or exercise in a hot/humid
environment = cumulative increase in HR
between bouts
recovery is not complete.
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Prolonged Exercise
• With prolonged aerobic exercise or aerobic
exercise in the heat, at a constant exercise
intensity:
– Gradual decrease in SV
(greater % of blood diverted to
skin for heat loss & decrease
in blood volume from sweating)
Therefore HR must increase
to maintain CO
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Cardiovascular drift
• Ability to maintain a constant CO despite a
decreasing SV which is due to the increase in
HR being equal in magnitude to the decline in
SV
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Cardiovascular drift - due to:
1. The influence of rising body temperature on
dehydration:
Progressive increase in the amount of CO
directed to the vasodilated skin to facilitate
heat loss
More blood in skin to cool the body
Less blood available to return to heart =
decreases SV
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2. A reduction in plasma volume:
Reduces venous return to the heart &
therefore reduces SV
• If prolonged exercise is performed in a
hot/humid environment, the increase in heart
rate and decrease in stroke volume is
exaggerated
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Regulation of cardiovascular adjustments
to exercise
• Initial signal to the cardiovascular system at
the beginning of exercise comes from higher
brain centers.
• However, fine tuning of the cardiovascular
response to exercise is accomplished via a
series of feedback loops from:
1.Muscle chemoreceptors
2. Arterial baroreceptors
3. Others.
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Arm vs. Leg Exercise
• At any given level of oxygen consumption both
HR and BP are higher during arm work compared
to leg work
• Higher HR from greater sympathetic stimulation
(SNS) to the heart during arm work.
• The relatively large increase in BP for arm work is
due to a vasoconstriction in the inactive muscle
groups (e.g. legs)
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Heart Rate and
Blood Pressure
During Arm
and Leg
Exercise