COPD (Chronic Obstructive Pulmonary Disease)

Cause

COPD is most often caused by smoking. Most people with COPD are long-term smokers, and research shows that smoking cigarettes increases the risk of getting COPD:²

• Out of every 100 long-term smokers, about 10 to 15 get COPD with symptoms. That means that about 85 to 90 out of 100 do not get COPD with symptoms.³
• Some studies show that up to half of long-term smokers older than age 45 get COPD.³

See a graph on how smoking affects the ability to breathe.

COPD is often a mix of two diseases: chronic bronchitis and emphysema. Both of these diseases are caused by smoking. Although you can have either chronic bronchitis or emphysema, people more often have a mixture of both diseases.

Chronic bronchitis

Almost all people with chronic bronchitis are, or have been, tobacco smokers. Over time, tobacco smoke and other lung irritants can lead to inflammation in the airways of the lungs (bronchial tubes ). As a result, the airways produce more mucus than they normally would. Inflammation and excess mucus cause coughing and narrow the airways. It is hard to breathe through the narrow airways, so you feel short of breath.

Long-term (chronic) mucus production and inflammation over many years may lead to permanent lung damage and may make it more likely that you will get lung infections.

Emphysema

In emphysema, tobacco smoke and other irritants can damage the elastic fibers in the lungs. These stretchy strands of tissue are needed for normal lung function. They allow the lung tissue to stretch when you breathe in and help pull the lungs back to their normal size and shape as you breathe out. When the elastic fibers are damaged:

• The tiny air sacs (alveoli) at the end of the bronchial tubes are damaged. These air sacs are where the blood exchanges carbon dioxide (a by-product of metabolism) for oxygen. When air sacs are damaged or destroyed, their walls break down and the sacs become larger. These large air sacs move less oxygen into the blood. After air sacs are destroyed, they cannot be replaced.
• The smaller airways in the lungs (bronchioles ) tend to collapse when you breathe out, trapping air in the alveoli. As a result, oxygen-rich air has trouble entering the air sacs. And carbon dioxide has a harder time getting out of the lungs.

See pictures of bronchitis and emphysema.

Other causes

Other possible causes of COPD include:

• Long-term exposure to lung irritants such as industrial dust and chemical fumes.
• Low birth weight and having repeated lung infections.
• Inherited factors (genes), including alpha-1 antitrypsin deficiency, a rare condition in which your body may not be able to make a protein (alpha-1 antitrypsin) that helps protect the lungs from damage. People with this disorder who smoke generally start to have symptoms of emphysema in their 30s or 40s. Those who have this disorder but do not smoke generally start to have symptoms in their 80s.

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Author:	Maria G. Essig, MS, ELS Cynthia Tank	Last Updated: May 8, 2008
Medical Review:	Caroline S. Rhoads, MD - Internal Medicine Ken Y. Yoneda, MD - Pulmonology
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