What Is Chronic Obstructive Pulmonary Disease (COPD)?

Tired African American man bending over outdoorsChronic obstructive pulmonary disease (COPD) is a lung disease in which the lung is damaged, making it hard to breathe. In COPD, the airways-the tubes that carry air in and out of your lungs-are partly obstructed, making it difficult to get air in and out.

Cigarette smoking is the most common cause of COPD. Most people with COPD are smokers or former smokers. Breathing in other kinds of lung irritants, like pollution, dust, or chemicals over a long period of time may also cause or contribute to COPD.

The airways branch out like an upside-down tree, and at the end of each branch are many small, balloon-like air sacs. In healthy people, each airway is clear and open, the air sacs are small and dainty, and both are elastic and springy. When you breathe in, each air sac fills up with air, like a small balloon, and when you breathe out, the balloon deflates and the air goes out. In COPD, the airways and air sacs lose their shape and become floppy. Less air gets in and less air goes out because:

•The airways and air sacs lose their elasticity (like an old rubber band)
•The walls between many of the air sacs are destroyed
•The walls of the airways become thick and inflamed (swollen)
•Cells in the airways make more mucus (sputum) than usual, which tends to clog the airways.

COPD develops slowly, and it may be many years before you notice symptoms like feeling short of breath. Most of the time, COPD is diagnosed in middle-aged or older people, and is a major cause of death and illness throughout the world.

It is the 4th leading cause of death in the U.S. and the world.

There is no cure for COPD. The damage to your airways and lungs cannot be reversed, but there are things you can do to feel better and slow the damage to your lungs.

COPD is not contagious-you cannot catch it from someone else.

Other Names for COPD

•Chronic obstructive airway disease
•Chronic obstructive lung disease

In the U.S., COPD includes:

•Emphysema
•Chronic Bronchitis

In the emphysema type of COPD, the walls between many of the air sacs are destroyed, leading to a few large air sacs, instead of many tiny ones (see How Do the Lungs Work). Then, the lung looks like a sponge with many large bubbles or holes in it, instead of a sponge with very even tiny holes. These few large air sacs have less surface area than the normal tiny ones for the exchange of oxygen and carbon dioxide. Poor exchange of the oxygen and carbon dioxide causes shortness of breath.

In chronic bronchitis, the airways have become inflamed and thickened and there is an increase in the number and size of the mucus-producing cells. This results in excessive mucus production, which in turn contributes to cough and difficulty getting air in and out of the lungs.

Most people with COPD have both chronic bronchitis and emphysema.

How Do the Lungs Work?

The lungs provide a very large surface area (the size of a football field) for the exchange of oxygen and carbon dioxide between the body and the environment.

A slice of normal lung looks like a pink sponge-filled with tiny bubbles or holes. Around each bubble is a fine network of tiny blood vessels. These bubbles, surrounded by blood vessels, give the lungs a large surface to exchange oxygen (into the blood where it is carried throughout the body) and carbon dioxide (out of the blood). This process is called gas exchange. Healthy lungs do this very well.

Here’s how normal breathing works:

You breathe in air through your nose and mouth. The air travels down through your windpipe (trachea) then through large and small tubes in your lungs called bronchial (BRON-kee-ul) tubes. The larger ones are bronchi (BRONK-eye), and the smaller tubes are bronchioles (BRON-kee-oles). Sometimes the word “airways” is used to refer to the various tubes or passages that air must travel through from the nose and mouth into the lungs. The airways in your lungs look something like an upside-down tree with many branches.

At the ends of the small bronchial tubes, there are groups of tiny air sacs called alveoli (al-VEE-uhl-EYE). The air sacs have very thin walls, and small blood vessels called capillaries run in the walls. Oxygen passes from the air sacs into the blood in these small blood vessels. At the same time, carbon dioxide passes from the blood into the air sacs. Carbon dioxide, a normal byproduct of the body’s metabolism, must be removed.

The airways and air sacs in the lung are normally elastic-that is, they try to spring back to their original shape after being stretched or filled with air, just the way a new rubber band or balloon would. This elastic quality helps retain the normal structure of the lung and helps to move the air quickly in and out. In COPD, much of the elastic quality is gone, and the airways and air sacs no longer bounce back to their original shape. This means that the airways collapse, like a floppy hose, and the air sacs tend to stay inflated. The floppy airways obstruct the airflow out of the lungs, leading to an abnormal increase in the lungs’ size. In addition, the airways may become inflamed and thickened and mucus-producing cells produce more mucus, further contributing to the difficulty of getting air out of the lungs.

In the type of COPD called emphysema, the walls between the air sacs are destroyed, leading to a few large air sacs, instead of many tiny ones. Then, the lung looks like a sponge with large bubbles or holes in it instead of a sponge with very even tiny holes. These few large air sacs have less surface area than the many tiny ones for the exchange of oxygen and carbon dioxide.

What Causes COPD?

Smoking is the most common cause of COPD. Most cases of COPD develop after repeatedly breathing in fumes and other things that irritate and damage the lung and airways. Cigarette smoking is the most common irritant that causes COPD. Pipe, cigar, and other types of tobacco smoking can also cause COPD, especially if the smoke is inhaled. Breathing in other fumes and dusts over a long period of time may also cause COPD. The lungs and airways are highly sensitive to these irritants. They cause the airways to become inflamed, narrowed, and destroy the elastic fibers that allow the lung to stretch, then come back to its resting shape. This makes breathing air in and out of the lungs more difficult.

Other things that may irritate the lungs and contribute to COPD include:

•Working around certain kinds of chemicals and breathing in the fumes for many years
•Working in a dusty area over many years
•Heavy exposure to air pollution.

Being around secondhand smoke (smoke in the air from other people smoking cigarettes) also plays a role in causing COPD. In addition, genes may play a role in developing COPD. In rare cases, COPD is caused by a gene-related disorder called alpha 1 antitrypsin deficiency. Alpha 1 antitrypsin is a protein in your blood that inactivates destructive proteins in the blood. People with antitrypsin deficiency have low levels of alpha 1 antitrypsin; the imbalance of proteins leads to the destruction of the lung and COPD. If people with this condition smoke, the disease progresses more rapidly.

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