What Is Chronic Obstructive Pulmonary Disease?

Chronic obstructive pulmonary disease (COPD), also called chronic obstructive lung disease, is a term that is used for two closely related diseases of the respiratory system: chronic bronchitis and emphysema.

In many patients these diseases occur together, although there may be more symptoms of one than the other. Most patients with these diseases have a long history of heavy cigarette smoking. Cigarette smoking is the most important risk factor for COPD.

COPD gets gradually worse over time. At first there may be only a mild shortness of breath and occasional coughing. Then a chronic cough develops with clear, colorless sputum. As the disease progresses, the cough becomes more frequent and more and more effort is needed to get air into and out of the lungs. In later stages of the disease, the heart may be affected. Eventually death occurs when the function of the lungs and heart is no longer adequate to deliver oxygen to the body's organs and tissues.

Cigarette smoking is the most important risk factor for COPD; it would probably be a minor health problem if people did not smoke. Other risk factors include age, heredity, exposure to air pollution at work and in the environment, and a history of childhood respiratory infections.

COPD attacks people at the height of their productive years, disabling them with constant shortness of breath. It destroys their ability to earn a living, causes frequent use of the health care system, and disrupts the lives of the victims' family members for as long as 20 years before death occurs.

What Goes Wrong With the Lungs and Other Organs in Chronic Obstructive Pulmonary Disease?

The most important job that the lungs perform is to provide the body with oxygen and to remove carbon dioxide. This process is called gas exchange, and the normal anatomy of the lungs serves this purpose well.

The lungs contain 300 million alveoli whose ultrathin walls form the gas exchange surface. Enmeshed in the wall of each of these air sacs is a network of tiny blood vessels, the capillaries, which bring blood to the gas exchange surface. When a person inhales, air flows from the nose and mouth through large and small airways into the alveoli. Oxygen from this air then passes through the thin walls of the inflated alveoli and is taken up by the red blood cells for delivery to the rest of the body. At the same time, carbon dioxide leaves the blood and passes through the alveolar walls into the alveoli. During exhalation, the lung pushes the used air out of the alveoli and through the air passages until it escapes from the nose or mouth.

When COPD develops, the walls of the small airways and alveoli lose their elasticity. The airway walls thicken, closing off some of the smaller air passages and narrowing larger ones. The passageways also become plugged with mucus. Air continues to get into alveoli when the lung expands during inhalation, but it is often unable to escape during exhalation because the air passages tend to collapse during exhalation, trapping the "stale" air in the lungs. These abnormalities create two serious problems which affect gas exchange: