Thursday, February 5, 2009

How Airways Narrow

During an asthma attack, some type of trigger causes your airway passages to narrow. Airway narrowing often involves two mechanisms, each of which requires separate treatment.

One component of airway narrowing is muscle contraction. The muscles surrounding the around your breathing tubes can contract quickly, in less than one minute, and squeeze the bronchial tubes so that they narrow. These breathing tubes are involuntary muscles, like the muscles that constrict pupils or move food through the intestines. When you encounter one of your asthma triggers, the muscles that form a ring muscles can also relax relatively quickly, in just a few minutes, either on their own or in response to medication. The terms used to describe these processes are bronchoconstriction or bronchospasm (when the tubes narrow) and bronchodilation (when they widen).

The other component of airway narrowing is inflammation, a biological process in which the body tries to heal various injuries, irritations, or infections. Inflammation generally involves some swelling caused by leakage of fluid from the blood vessels, and an influx of specialized cells to the scene of an injury or infection.
In asthma, inflammatory cells come out of the blood and take up residence in the walls of the bronchial tubes. These inflammatory cells contain powerful chemicals that can cause the walls of the bronchial tubes to swell and produce extra mucus, or phlegm. (Mucus that is coughed up is called sputum, although most people use mucus, phlegm, and sputum interchangeably.) The mucus can plug the bronchial tubes, leaving little room for air to move in and out. Both the swelling of the airway walls and the accumulation of excess mucus can contribute to the breathing problems of asthma. Unlike muscle contraction around the bronchial tubes, inflammation of the bronchial tube walls takes many hours or even days to subside.

Medications used to treat asthma focus on these two mechanisms of airway narrowing. Some drugs are designed to relax the muscles surrounding the airways; others reduce inflammation of the breathing tubes. Some do both.

No comments:

Post a Comment