Causes

Smoking is unequivocally the No. 1 cause of COPD, which is why it is considered to be a very preventable disease. This conclusion is justified by the fact that, at least in the United States, the condition is seen so uncommonly among nonsmokers. Smoking can damage both the airways and air sacs. In emphysema, the walls of the air sacs are damaged and individual air sacs collapse into fewer, larger air sacs, which lose their ability to transfer gases in and out of the bloodstream. In addition, air is trapped in these large, diseased, nonfunctional air sacs. Over time, this causes the air sacs, and the lungs, to become bigger (hyperinflate), especially with exercise; the hyperinflation is accompanied by increased difficulty breathing and shortness of breath. (To demonstrate, take a deep breath and then, while holding the air in your hyperinflated lungs, attempt to take a series of normal breaths.)

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In chronic bronchitis, excessive amounts of mucus are produced. This mucus is often of poor quality--tenacious and difficult to expel, even with coughing. This mucous defense against bacteria, viruses, and other foreign particles is seriously compromised, and these particles remain in the lungs to cause infection and inflammation. It then becomes increasingly difficult for the already damaged cilia to sweep the particle-laden mucus out of the lungs. The retained mucus further narrows the airways, and this narrowing acts in concert with hyperinflation to make it even more difficult to breathe.