COPD Overview

What is chronic obstructive pulmonary disease (COPD)?

COPD stands for chronic obstructive pulmonary (lung) disease. COPD is a term applied to a family of diseases that includes emphysema, chronic bronchitis, and emphysema due to alpha-1 antitrypsin deficiency. COPD usually progresses gradually, causing limited airflow in and out of the lungs.

COPD adds to the work of the heart. Diseased lungs might reduce the amount of oxygen that goes to the blood. High blood pressure in blood vessels from the heart to the lungs makes it difficult for the heart to pump. Lung disease can also cause the body to produce too many red blood cells, which might make the blood thicker and harder to pump.

Patients who have COPD with low oxygen levels might develop an enlarged heart (cor pulmonale). This condition weakens the heart and causes increased shortness of breath, and swelling in the legs and feet.

The good news is that COPD is treatable, and the information in this manual can help you manage your COPD and flare-ups, and help you to modify your risk factors.

Chronic bronchitis

Chronic bronchitis is irritation and inflammation (swelling) of the lining in the bronchial tubes (air passages). The irritation causes coughing and an excess amount of mucus in the airways. The swelling makes it difficult to get air in and out of the lungs. The small, hair-like structures on the inside of the airways (called cilia) might be damaged by the irritation. The cilia are then unable to help clean mucus from the airways.

Bronchitis is generally considered chronic when you have: a productive cough (cough up mucus) and shortness of breath that lasts about three months or more each year for two or more years in a row. Your doctor might define chronic bronchitis differently.


Emphysema is the destruction, or breakdown, of the walls of the alveoli (air sacs) located at the end of the bronchial tubes. The damaged alveoli are not able to exchange oxygen and carbon dioxide between the lungs and the blood. The bronchioles lose their elasticity and collapse when you exhale, trapping air in the lungs. The trapped air keeps fresh air and oxygen from entering the lungs.

Who is affected by COPD?

Emphysema and chronic bronchitis affect approximately 23 million people in the United States, or close to 13 percent of the population.

What causes chronic obstructive pulmonary disease (COPD)?

The two primary causes of COPD are cigarette smoking and alpha-1 antitrypsin (AAT) deficiency. Air pollution and occupational dusts might also contribute to COPD, especially when the person exposed to these substances is a cigarette smoker. Genetic causes other than AAT deficiency are also likely to contribute.

Cigarette smoke causes COPD by irritating the airways and creating inflammation that narrows the airways, making it more difficult to breathe. Cigarette smoke also causes the cilia to stop working properly so mucus and trapped particles are not cleaned from the airways. As a result, chronic cough and excess mucus production develop, leading to chronic bronchitis.

In some people, chronic bronchitis and infections can lead to destruction of the small airways, or emphysema.

Alpha-1 antitrypsin (AAT) deficiency, an inherited disorder, can also lead to emphysema. Alpha-1 antitrypsin is a protective enzyme that is produced in the liver, secreted into the bloodstream from the liver cells, and then carried through the blood to the lungs to help fight inflammation.

When there is not enough AAT in the lung, the body is no longer protected from the tissue breakdown effects of an enzyme in the white blood cells. When the white blood cells go to the lung (for instance, in conditions of lung inflammation like smoking or dusty environments), they release these enzymes into the lung. This can cause a breakdown in the walls of the air sacs (alveoli). When the alveoli are destroyed, air passages of the lung can become blocked, oxygen cannot be transferred into the blood, and carbon dioxide cannot be taken from the blood to be exhaled.

What are symptoms of chronic obstructive pulmonary disease (COPD)?

  • Shortness of breath
  • Shortness of breath with mild exercise (walking, using the stairs, etc.)
  • Chronic, productive cough (with mucus)
  • A feeling of "tightness" in the chest
  • Wheezing

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy