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
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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