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How Asthma Works

Inflammation

The most important thing to know about how asthma works is that it is a disease of inflammation. All of the other components of asthma stem from that central problem.

Inflammation is a common process throughout the body, and it is not all bad. For instance, picture scratching your arm accidentally on a nail. The area right around the scratch becomes dark pink, maybe somewhat hot and puffy. And it hurts. Warmth, redness, swelling, and pain are the hallmarks of inflammation. A small amount of fluid may also seep out - this is common in inflamed tissues (medically, the fluid is called "exudate.")

In the case of a nasty scratch, inflammation is the process the body uses to reduce the likelihood of infection and to promote repair. The symptoms will probably last a couple of days and then go away once the wound has effectively healed. There are times, though, when the standard (and usually useful) bodily process of inflammation gets out of hand, resulting in an inflammatory disease. Asthma is not the only inflammatory disease. Some others include:

  • Rheumatoid arthritis (inflammation in the joints)
  • Inflammatory bowel disease (inflammation in the intestine)
  • Lupus (an inflammatory disease that can affect many different parts of the body, including the skin, kidneys, and lungs)

In asthma, of course, the inflammation is located in the airways. Even when a person with asthma is not having an asthma attack and seems to be breathing okay, the walls of his or her airways remain inflamed. They are swollen and produce too much mucus, dramatically shrinking the space available for air to get through. This is why medicines to reduce inflammation (especially inhaled corticosteroids) are at the center of most asthma treatment plans.
In addition to its direct effects, inflammation contributes (in ways we do not fully understand) to the other two major problems in asthma-- airway hyperresponsiveness and excessive bronchoconstriction.)

Airway Hyperresponsiveness

Physicians often refer to asthmatic airways as "twitchy" because they are terribly sensitive to things that would cause no noticeable effect on the airways of non-asthmatics. (The medical term for this "twitchiness" is hyperresponsiveness.) Just walking into cold air, or sitting near someone wearing perfume, for example, can trigger a big reaction in the airways of an asthmatic. The airway walls swell up even more, the airway muscles squeeze, and the person with asthma can find himself wheezing, coughing, and maybe even having trouble breathing at all. Doctors have noted, however, that if the inflammation in an asthmatic person's airways is controlled by medicines, the airways become much less "twitchy."

Excessive Bronchoconstriction

Airways are hollow tubes through which air passes. The tubes themselves are made up of different layers of tissue, one of which is a layer of smooth muscle. In a person with asthma, the airway muscles tend to be particularly large and strong.

When a response of the airways is triggered, the muscles contract, squeezing the airway and narrowing the space that air can get through. The smooth muscle of the airway in a person with asthma contracts too easily, too hard, and too long. As discussed above, the airways of asthmatics are already swollen and partly filled with mucus, so the extra squeezing of the airway smooth muscle can make it difficult or even impossible for any air to get through at all.

Excessive contraction of airway muscle appears to be directly related to airway inflammation. Controlling the inflammation with anti-inflammatory medicines helps prevent the muscles squeezing so easily and so hard, and thus, helps prevent asthma episodes.

"Rescue" or "reliever" medicines (such as albuterol, Ventolin, and Proventil) work by making the airway smooth muscle relax, to temporarily stop them from squeezing the airway closed. They do nothing, though, for the inflammation that is at the root of the problem.