The upper and lower airways (above and below the glottis), lung, and chest wall function as an integrated unit to provide for efficient gas exchange during exercise and sports. Dysfunction in any of these components can lead to compromised exercise tolerance. This chapter will consider common conditions that affect the respiratory tract and that can lead to limitation in physical activities. Locating the site of dysfunction through physical examination and laboratory testing, particularly the evaluation of pulmonary function is the first step in solving a sports-related respiratory problem. Consideration of pulmonary function alterations together with signs and symptoms of disease and specific therapies will be the focus of this chapter. Consequently, a general discussion of respiratory exercise physiology and pulmonary function evaluation will form the basis for understanding specific conditions that affect each.
Respiratory Exercise Physiology
There is a significant and interdependent interaction of muscle, cardiovascular output, and ventilation during rest as well as during exercise. Ventilation is dependent on airway caliber, integrity of the central and peripheral nervous system, and respiratory musculature. During quiet breathing, the diaphragm and to some extent the abdominal muscles and inspiratory intercostal muscles are active. With exercise, there is considerable increase in activity of these muscle groups in addition to recruitment of other muscles including the expiratory intercostals and sternocleidomastoids. The sum total is increased ventilation to meet the metabolic demands of more vigorous exercise including increased oxygen consumption and carbon dioxide elimination.
At high levels of exercise, all respiratory muscles are participating and movement of extremities also facilitates breathing.1 Increase in all the body's muscle activity requires increased oxygen consumption and during strenuous exercise up to 95% of oxygen demands can be accounted for by respiratory and other muscles groups.1 The physiologic adjustments for adequate oxygen consumption to support aerobic metabolism and provide adequate elimination of carbon dioxide are dependent on the linked factors shown in Figure 12-1. These are specifically increased ventilation, increased cardiac output, and redistribution of blood flow to working muscles.1 When oxygen requirements to support aerobic metabolism are exceeded, anaerobic metabolism begins. Increased lactate is the end product. During exercise, the point of transition from aerobic to anaerobic metabolism (the anaerobic threshold) is measured in the laboratory. This will vary with level of conditioning or with disease state (Figure 12-2).2
Gas transport mechanism for the coupling of cellular to pulmonary respiration. Qo2, oxygen extraction of muscle from blood; Qco2, carbon dioxide production from muscle activity; Vo2, volume of oxygen taken up by the lung; Vco2, volume of carbon dioxide during expiration. (Used with permission from reference 2)
Change in lactate level versus oxygen consumption (Vo2) in ...