People with healthy lungs rarely use all the gas-exchange potential of their lungs. During the most strenuous activity, a healthy person will use only 60% to 70% of their maximal ventilatory capacity. Strenuous exercise does cause temporary dyspnea (shortness of breath), but the 30% to 40% ventilatory reserve quickly relieves the dyspnea of a healthy person after a short rest. Even the dyspnea caused by strenuous exercise in a healthy person is not as debilitating as the dyspnea in a person with severe COPD.
Healthy lungs function less efficiently as they age. As people get older their chest walls stiffen and their respiratory muscles weaken. Both changes make breathing almost twice as much work for a 70-year-old as for a 20-year-old. The forced vital capacity (VC or FVC) and the amount of air that can be exhaled in a second (1-second forced expiratory volume, or FEV1) gradually and progressively decline during a person’s lifetime. In a healthy person, none of these natural lung changes approaches the dramatic declines caused by COPD. The natural decline in lung function worsens the already compromised breathing of those elderly people who have COPD