Johnny Carson (search), late-night talk show host for 30 years, died from emphysema (search), a common lung disease.

Carsonwas diagnosed with emphysema in 2002.

What is emphysema, can it be prevented, and how can it be treated? WebMD turned to The Cleveland Clinic and the American Lung Association for answers.

What is emphysema?

Emphysema is irreversible destruction of the walls of the air sacs located at the end of the bronchial tubes (search). The damaged air sacs, called alveoli (search), are not able to exchange oxygen and carbon dioxide between the lungs and the blood. As a result a person develops progressive symptoms of the disease including shortness of breath, cough, and limited ability to exert him- or herself.

The lung tissue loses its elasticity and collapses when the person exhales, trapping air in the lungs. The trapped air keeps fresh air and oxygen from entering the lungs.

What causes emphysema?

Cigarette smoking causes approximately 80 to 90 percent of deaths due to emphysema. Air pollution and occupational dusts may also contribute to emphysema, especially when the person exposed to these substances is a cigarette smoker. A genetic abnormality called alpha-1-antitrypsin deficiency (search) can also cause emphysema.

Cigarette smoke causes emphysema by destroying the tiny air sacs in the lungs. Damage to these air sacs leads to holes in the lung tissue. It typically takes years of smoking before emphysema symptoms develop -- but once the damage is done, it can’t be reversed.

How many people have emphysema?

The number of people with emphysema has gone from 2.3 million in 1982 to 3.1 million in 2002. Many people with emphysema also have chronic bronchitis (search), another lung condition largely caused by smoking. Heart disease, also commonly caused by smoking, is also often present.

Emphysema generally occurs after the age of 45. Men tend to develop emphysema more frequently. However, it’s unclear if emphysema rates in women will rise since smoking is now more common among women.

Together with other lung conditions that are largely caused by smoking, such as chronic bronchitis, emphysema is the fourth leading cause of death in the U.S., claiming the lives of more than 120,000 Americans per year.

What are the symptoms of emphysema?

Early symptoms include shortness of breath and cough. People with emphysema often also have chronic bronchitis, in which the person develops a long-lasting cough that produces mucus. Wheezing is often also present in people with emphysema.

How is emphysema treated?

Lung damage due to emphysema is irreversible. The single most important treatment is to stop smoking. Quitting smoking helps slow the progression of emphysema. Treatment also improves shortness of breath.

Medications, including inhalers to help relax the lung and open the airways, are often used. Anti-inflammatory steroids are also used if the person has a sudden worsening with increased shortness of breath.

Exercise can be very helpful to help strengthen the breathing muscles and improve overall condition.

Rarely, surgery is performed. Lung transplantation can be effective in some cases. A relatively new surgery, called lung volume reduction surgery, can help improve breathing. In this surgery the most severely diseased portion of the lung is removed. This procedure is very risky in people with very severe emphysema and research has shown that these people are at an increased risk of death with this surgery.

What is the prognosis of emphysema?

Although emphysema cannot be cured, its symptoms can be treated and your quality of life can be improved. The prognosis or outlook for the future depends on how well the lungs are functioning, symptoms, and how well the person responds to and follows treatment.

Can emphysema be prevented?

Since most people who develop emphysema are smokers, the best way to prevent this lung disease is not to smoke.

By Michael W. Smith, MD, reviewed by Brunilda Nazario, MD

SOURCES: The Cleveland Clinic. American Lung Association.