Copyright © 2008 Thomson Delmar Learning CHAPTER 18 Exercise and Its Effects on the Cardiopulmonary...

Copyright © 2008 Thomson Delmar Learning

CHAPTER 18

Exercise and Its Effects on the Cardiopulmonary System

Copyright © 2008Thomson Delmar Learning

VENTILATION


CONTROL OF VENTILATION


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.


ALVEOLAR VENTILATION


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).


OXYGEN CONSUMPTION


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.


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.


Arterial Blood Gas Levels During Exercise

Fig. 18-4. The effect of oxygen consumption on PaO2 and PaCO2 as the intensity of exercise increases.


OXYGEN DIFFUSION CAPACITY


Oxygen Diffusion Capacity

Fig. 18-5. Oxygen diffusion capacity increases linearly in response to increased oxygen consumption as the intensity of exercise increases.


Alveolar-Arterial PO2 Difference

Fig. 18-6. The alveolar-arterial oxygen tension difference P(A-a)O2 begins to increase when approximately 40 percent of the maximal VO2 is exceeded.


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


• 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.

Sympathetic Discharge


Cardiac Output

• Increased oxygen demands during exercise are met almost entirely by an increased cardiac output.


Cardiac Output

Fig. 18-7. A linear relationship exists between cardiac output and the intensity of exercise.


Cardiac Output

• Increased cardiac output during exercise results from:

1. Increased stroke volume

2. Increased heart rate, or

3. Combination of both


Increased Heart Rate

• An individual’s maximum heart rate (MHR) is estimated as follows:


Increased Heart Rate

• Thus, the maximum heart rate for a 45-year-old person is about 175:


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


Venous Vascular Pressure

• An oxygen consumption and cardiac output increase during exercise

• Mean pulmonary arterial and wedge pressure also increase linearly


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.


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


INTERRELATIONSHIPS BETWEEN MUSCLE

WORK, OXYGEN CONSUMPTION, AND

CARDIAC OUTPUT


Muscle Work, Oxygen Consumption, and Cardiac Output

Fig. 18-9. Relationship between muscle work, oxygen consumption, and cardiac output.


THE INFLUENCE OF TRAINING ON THE HEART

AND CARDIAC OUTPUT


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.


BODY TEMPERATURE/CUTANEOUS BLOOD FLOW RELATIONSHIP


Cardiopulmonary Rehabilitation

• Phase I• Phase II• Phase III

Copyright © 2008 Thomson Delmar Learning CHAPTER 18 Exercise and Its Effects on the Cardiopulmonary...

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