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Exercise and the Heart
O2 Delivery
 Q increase is in direct
proportion to the O2
demand of the
muscles
 Heart Rate
 Stroke Volume
 Blood pressure
 Systolic
 Diastolic
 a-v O2 Difference
Redistribution of Blood Flow
 Muscle blood flow to working
skeletal muscle
 Splanchnic blood flow  to less
active organs (Liver, kidneys, GI
tract, etc.)
Redistribution of Blood Flow
During Exercise
Fig 9.19
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Redistribution of Blood Flow
Increased Blood Flow to Skeletal
Muscle During Exercise
 How?
 Withdrawal of sympathetic
vasoconstriction
 Autoregulation
 Blood flow increased to meet metabolic
demands of tissue
 Vasodilation:  O2 tension,  CO2
tension, pH, potassium, adenosine,
nitric oxide
Circulatory Responses to
Exercise
 Depend on:
 Type, intensity, and duration of
exercise
 Environmental condition
 Emotional influence
Transition From Rest  Exercise
and Exercise  Recovery
 Rapid increase in HR, SV, cardiac
output
 Plateau in submaximal (below
lactate threshold) exercise
 O2 supply = O2 demand
 Recovery depends on:
 Duration and intensity of exercise
 Training state of subject
O2 supply = O2 demand
O2 supply < O2 demand
Transition
From Rest
 Exercise
 Recovery
Recovery
 O2 supply > O2 demand
 What is the extra oxygen used for?
 Restore O2 inside muscles (myoglobin)
 Removal of lactic acid
 Reduce body temperature
Incremental Exercise
Heart rate and cardiac output
 Increases linearly with increasing work
rate
 Reaches plateau at 100% VO2max
Systolic blood pressure
 Increases with increasing work rate
Incremental Exercise
 Stroke Volume
 Reaches
plateau at 4060% VO2max
 Why?
Arm vs. Leg Exercise
 At the same oxygen uptake arm work
results in higher:
 Heart rate
 Due to higher sympathetic stimulation
 Blood pressure
 Due to vasoconstriction of large inactive
muscle mass
.
Heart Rate
and Blood
Pressure
During Arm
and Leg
Exercise
Prolonged Exercise
 Cardiac output is maintained
 Gradual decrease in stroke volume
 Gradual increase in heart rate
 Cardiovascular drift
 Due to dehydration and increased
skin blood flow (rising body
temperature)
Fig 9.22
.
HR, SV, and CO During
Prolonged Exercise
Fig 9.22
Cardiovascular Adjustments
to Exercise
Fig 9.23
Summary of Cardiovascular
Control During Exercise
Initial signal to “drive”
cardiovascular system comes
from higher brain centers
Fine-tuned by feedback from:
Chemoreceptors
Mechanoreceptors
Baroreceptors
Fig 9.24
A Summary
of
Cardiovasc
ular
Control
During
Exercise
Fig 9.24