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CHAPTER 18
Exercise and Its Effects on the
Cardiopulmonary System
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VENTILATION
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CONTROL OF
VENTILATION
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Mechanisms by Which Exercise Stimulates Ventilation
Fig. 18-1. Mechanisms by
which exercise stimulates
ventilation. (1) Collateral
fibers form the motor neurons
travel to the medulla; (2)
sensory signals from the
exercising limbs are sent to
the medulla; the increase in
body temperature during
exercise may also increase
ventilation.
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ALVEOLAR VENTILATION
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Exercise and Ventilation
Fig. 18-2. The relationship
of exercise and ventilation.
Note the abrupt increase in
ventilation at the outset of
exercise (A) and the even
larger, abrupt decrease in
ventilation at the end of
exercise (B).
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OXYGEN CONSUMPTION
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Oxygen Consumption (VO2) and Alveolar Ventilation
Fig. 18-3. There is a linear
relationship between oxygen
consumption (VO2) and
alveolar ventilation as the
intensity of exercise
increases.
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Oxygen Consumption
• When anaerobic threshold is reached
during strenuous exercise
– Linear relationship between VO2 and alveolar
ventilation will no longer exist.
• When the anaerobic threshold is reached
– Abrupt increase in alveolar ventilation with
little or no increase in VO2.
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Arterial Blood Gas Levels During Exercise
Fig. 18-4. The effect of
oxygen consumption on PaO2
and PaCO2 as the intensity of
exercise increases.
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OXYGEN DIFFUSION
CAPACITY
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Oxygen Diffusion Capacity
Fig. 18-5. Oxygen diffusion
capacity increases linearly
in response to increased
oxygen consumption as
the intensity of exercise
increases.
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Alveolar-Arterial PO2 Difference
Fig. 18-6. The alveolararterial oxygen tension
difference P(A-a)O2 begins to
increase when approximately
40 percent of the maximal
VO2 is exceeded.
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Circulation
• During exercise, three essential
physiologic responses must occur for
the circulatory system to supply working
muscles with an adequate amount
of blood:
1. Sympathetic discharge
2. Increase in cardiac output
3. Increase in arterial blood pressure
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Sympathetic Discharge
• At the onset of exercise, the brain
transmits signals to the vasomotor
center, which has two circulatory effects:
– The heart is stimulated to increase its rate
and strength of contraction.
– Blood vessels of the peripheral vascular
system constrict, except for blood vessels
of the working muscles.
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Cardiac Output
• Increased oxygen demands during
exercise are met almost entirely by
an increased cardiac output.
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Cardiac Output
Fig. 18-7. A linear
relationship exists between
cardiac output and the
intensity of exercise.
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Cardiac Output
• Increased cardiac output during exercise
results from:
1. Increased stroke volume
2. Increased heart rate, or
3. Combination of both
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Increased Heart Rate
• An individual’s maximum heart rate
(MHR) is estimated as follows:
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Increased Heart Rate
• Thus, the maximum heart rate for a
45-year-old person is about 175:
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Arterial Blood Pressure
• There is an increase in arterial blood
pressure during exercise because of the:
1. Sympathetic discharge
2. Increased cardiac output
3. Vasoconstriction of the blood vessels
in the nonworking muscle areas
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Venous Vascular Pressure
• An oxygen consumption and cardiac
output increase during exercise
• Mean pulmonary arterial and wedge
pressure also increase linearly
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Pulmonary Arterial and Wedge Pressure
Fig. 18-8. The systolic,
diastolic, and mean
pulmonary arterial and
wedge pressure increase
linearly as oxygen
consumption and cardiac
output increase.
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Muscle Capillaries
• At rest, about 20 to 25 percent of the
muscle capillaries are dilated
• During heavy exercise, capillaries dilate
to facilitate distribution of blood
• This reduces the distance that oxygen
and other nutrients must travel from the
capillaries to the muscle fibers
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INTERRELATIONSHIPS
BETWEEN MUSCLE
WORK, OXYGEN
CONSUMPTION, AND
CARDIAC OUTPUT
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Muscle Work, Oxygen Consumption, and Cardiac Output
Fig. 18-9. Relationship
between muscle work,
oxygen consumption,
and cardiac output.
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THE INFLUENCE OF
TRAINING ON THE HEART
AND CARDIAC OUTPUT
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Stroke Volume Versus Heart Rate and Cardiac Output
Fig. 18-10. Approximate
changes in stroke volume
and heart rate that occur
when the cardiac output
increases from about 5 L/min
to 30 L/min in a marathon
runner.
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BODY TEMPERATURE/
CUTANEOUS BLOOD
FLOW RELATIONSHIP
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Cardiopulmonary Rehabilitation
• Phase I
• Phase II
• Phase III
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