Emphysema Causes

When you inhale, air travels to your lungs through two major airways off the windpipe (trachea) called bronchi. Inside your lungs, the bronchi subdivide like the roots of a tree into a million smaller airways (bronchioles) that finally end in clusters of tiny air sacs (alveoli). You have about 300 million air sacs in each lung.

Within the walls of the air sacs are tiny blood vessels (capillaries) where oxygen is added to your blood and carbon dioxide — a waste product of metabolism — is removed. The air sac walls also contain elastic fibers that help the very small airways leading to the air sacs expand like small balloons when you breathe.

What happens in emphysema
In emphysema, inflammation destroys these fragile walls of the air sacs, causing them to lose their elasticity. As a result, the bronchioles collapse, and air becomes trapped in the air sacs, which overstretches them and interferes with your ability to exhale (hyperinflation).

In time, this overstretching may cause several air sacs to rupture, forming one larger air space instead of many small ones. Because the larger, less elastic sacs aren't able to force air completely out of your lungs when you exhale, you have to breathe harder to take in enough oxygen and to eliminate carbon dioxide.

The process works something like this: Normally, you exhale in two ways, actively and passively. When you sit quietly, your diaphragm contracts and your chest muscles expand to take air in, but your muscles don't actively contract to let the air out. Instead, the elastic tissue around your air sacs contracts and your lungs passively shrink. On the other hand, when you exert yourself and need more oxygen, your chest muscles contract, forcing air out rapidly.

But if you have emphysema, many of these elastic fibers have been destroyed, and you must consciously force air out of your lungs. The forced exhalation compresses many of your small airways, making expelling air even more difficult.

Most common cause is smoking
Cigarette smoke is by far the most common cause of emphysema. The damage begins when tobacco smoke temporarily paralyzes the microscopic hairs (cilia) that line your bronchial tubes. Normally, these hairs sweep irritants and germs out of your airways. But when smoke interferes with this sweeping movement, irritants remain in your bronchial tubes and infiltrate the alveoli, inflaming the tissue and eventually breaking down elastic fibers.

Protein deficiency sometimes plays a role
In a small percentage of people, emphysema results from low levels of a protein called alpha-1-antitrypsin (AAt), which protects the elastic structures in your lungs from the destructive effects of certain enzymes. A lack of AAt can lead to progressive lung damage that eventually results in emphysema. If you're a smoker with a lack of AAt, emphysema can begin in your 30s and 40s.

AAt deficiency is a hereditary condition that occurs when you inherit two defective genes, one from each parent. Although severe AAt deficiency is rare, millions of people carry a single defective AAt gene. Some of these people have mild to moderate symptoms; others have no symptoms at all. Carriers are at increased risk of lung and liver problems and can pass the defect to their children.

People with two defective genes have a high likelihood of developing emphysema, usually between the ages of 30 and 40. The progression and severity of the disease are greatly exacerbated by smoking.

Experts recommend that people with early-onset emphysema — especially those who don't smoke or who have other risk factors for the disease or who have a family history of AAt deficiency — be tested for the defective gene. People who are found to have a genetic predisposition for AAt deficiency may want to consider having close family members tested as well.