Chronic obstructive pulmonary disease (COPD) is, I think, one of the most misunderstood common lung diseases. It is very important, as it is the 4th most common cause of death in the US, and the only common cause of death that is becoming more common, in contrast to, say, heart disease and many forms of cancer, which are getting better and better treatment. In my experience (and one that is shared by many other lung specialists) is that patients are often told that they have “asthma” or “COPD/asthma.” Some of the confusion comes from the fact that asthma and COPD are indeed very similar. Both diseases cause shortness of breath, cough, and a feeling of chest tightness. Both diseases produce abnormal lung sounds, such as wheezing (a high-pitched “whistling” noise) or rhonchi (a lower-pitched “snoring” noise) when someone listens to the lungs with a stethoscope. Tests to distinguish between the two diseases are imperfect, and it is often the clinical judgment of the doctor (or other health care professional) that determines whether asthma or COPD is present. In some patients, both asthma and COPD may exist.
At a fundamental level, however, the diseases are quite different, according to most researchers and experts. The inflammation of asthma is more like allergic inflammation, featuring eosinophils (a kind of white blood cells that is important in producing allergic symptoms) and a kind of antibody known as IgE. Asthma, though it may be persistent, more often follows a course of relatively long periods of stability with short episodes of sudden worsening, frequently in response to a sudden change in the environment, such as more pollen in the air. The inflammation that causes COPD is more chronic in nature, occurring after years and years of exposure to the cause, which in the US and other industrialized nations is cigarette smoke in more than 90% of cases. (In less industrialized nations, bad air pollution and long-term exposure to wood- or coal-burning fires in poorly ventilated areas may cause COPD.)
COPD is actually a combination of diseases, with most patients affected by both chronic bronchitis and emphysema. Less common diseases, such as bronchiectasis (chronic bacterial infection and inflammation of airways) sometimes also contribute. Chronic bronchitis is a condition in which there is long-standing inflammation of the airways (bronchi), leading to increased secretion of mucus, tightening of the muscles that line the walls of the airways, and eventually changes in and destruction of the architecture of the airways. Emphysema is the destruction of the alveoli (air sacs), where oxygen reaches the blood. Destruction of the air sacs leads to abnormal over-expansion of the lungs, with large cyst-like structures replacing normal air sacs. As a result of this over-expansion, the diaphragm and the other muscles that expand the chest to allow breathing have a harder time working, and patients with COPD often feel more tired from breathing, and they have a harder time breathing during physical effort.