COPD stands for chronic obstructive pulmonary disease.
Chronic obstructive pulmonary disease is a condition in which people have difficulty getting air out of their lungs. When you breathe, your diaphragms move down, your chest cavity expands and just like a bellows that causes you to suck air into your lungs. When you exhale, your diaphragms move up and your chest cavity, your rib cage relaxes and goes into a more neutral, resting position, and that squeezes the lungs just like a bellows will squeeze its air sac and push air out.
The problem in people with chronic obstructive pulmonary disease is that their airways have lost their elasticity.
When you think about the concept of elasticity, take a look at your skin. When skin is young and healthy, you pull up on the skin, it snaps back into its original position just like a rubber band. When you stretch a rubber band and let it got, it comes right back into its original position.
The same concept applies to your lung airways. Your lung airways have a nice, circular shape to them and they are able to maintain that shape while you take breaths in and exhale breaths out.
However, with chronic exposure to cigarette smoke or other lung irritants like air pollution, the elasticity of the tube itself becomes diminished, and as a result the lung can actually compress the airway when you are exhaling and pull the airway open when you are inhaling.
Upon exhalation, if the airways are compressed, whatever air remains in the air sacs can get trapped. As a result, people with COPD, tend to take a longer time to exhale. In situations where you would breathe quicker as a result of walking or exercising, the lungs will not have enough time for the air to get out of the lungs completely because of this narrowing on exhalation. This results in the progressive “trapping” of air with each breath.
Eventually, with all this air trapping, the rib cage starts to expand dramatically. The diaphragms come down significantly to the point that the lungs cannot open anymore just like when a bellows opens, it can only open but so far. Eventually with air trapping, there can be so much trapped air that the lungs can no longer bring air in. This is the reason why people with COPD can become very short of breath and have a sensation that they cannot get air in.