Exercise Physiology A Tale of Two Pumps

Learning Objectives

To delineate the ways in which the elements of the respiratory system—the controller, ventilatory pump, and gas exchanger—adapt to the metabolic stress of exercise.
To describe the changes that occur in acid–base balance during exercise and the body’s adaptations to those changes.
To define the respective roles of the respiratory and cardiovascular systems in supporting the metabolic needs of the body during exercise.
To demonstrate the integrated nature of the physiology of the cardiopulmonary systems in the delivery of oxygen to metabolically active tissue.
To create a framework for understanding exercise physiology in the context of two pumps (respiratory and cardiac) and two gas exchangers (pulmonary capillary and systemic capillary).
To outline the physiological limits of exercise in individuals with normal cardiopulmonary systems.

You are rounding the corner on the last lap of the mile run. Although you are in the lead, you are being chased by an opponent who is rapidly closing the gap. You are moving large volumes of air into and out of your lungs. You can feel your heart pounding. You are breathing heavily and have a sense of gasping for air. You feel like you just can’t go any faster, and you’re not sure that you will even be able to make it to the finish line. Why can’t you drive your body further? How is the respiratory system responding to the demands placed on it by this intense physical effort? What is limiting you—your respiratory system, or your cardiovascular system?

To this point, we have discussed, in turn, each of the components of the respiratory system. In Chapter 8, we examined how the function of the different elements contributes to respiratory sensations. Now we will investigate the manner in which the three components— the controller, ventilatory pump, and gas exchanger—work together in an integrated manner to enable the body to meet its greatest normal physiological stress: exercise. What you learn in this chapter is also applicable to pathologic states that stress the body in similar ways. Severe infections, for example, often lead to a range of physiologic responses that we term sepsis and that are characterized by changes quite similar to what is observed during exercise.

To fully understand exercise physiology, however, and to answer the questions posed in the first paragraph, we must also explore aspects of the function of the cardiovascular system. Those who have already studied cardiovascular physiology may come to appreciate a common framework between the respiratory and cardiovascular systems. Those who have not yet encountered this material before will be introduced to concepts that will have a striking similarity to those you are mastering in your explorations of the respiratory system. If this is your first taste of cardiovascular physiology, do not feel discouraged if you do not fully grasp all of the material. The framework we outline may be of assistance to you when you come to this material more fully in your studies. In the final analysis, exercise physiology is a tale of two pumps—the ventilatory pump and the cardiac pump—and two capillary beds or gas exchangers that provide for the transfer of oxygen from air to blood to metabolically active tissue and a similar transfer of carbon dioxide in the opposite direction.