sthma is a respiratory disorder marked by breathing difficulty caused by temporary narrowing of the bronchi, the airways branching from the trachea to the lungs. Attacks usually are brought on by allergic reaction to
ANTIGENS such as grass and tree pollens, mold spores, fungi, animal dander, and certain foods but may also be caused by chemical irritants in the atmosphere or by infections of the respiratory tract. Susceptibility to an asthma attack is based on hyperactivity of the bronchial muscles, which constrict on exposure to one or another of these agents. Episodes of asthma vary widely in severity and may last from a few minutes to several days.
They may begin at any age but usually occur in childhood. In children, asthma often is associated with eczema, a skin inflammation that may reflect the tendency of the child to develop hypersensitivity reactions. The attacks usually become less frequent and less severe over the years and disappear in about half of all affected children before adulthood. In one form of asthma, called intrinsic asthma, however, the attacks become less frequent and less severe, but recovery between them is less complete. The bronchi in such patients become chronically narrowed, causing a progressive loss of capacity for physical exertion. The prevalence of asthma is only about 1 or 2 percent worldwide but varies greatly from country to country. In the United
States, asthma affects about 6.9 percent of children. Typically, an asthma attack begins within minutes after exposure to a triggering agent.
Symptoms include a sensation of tightness in the chest, coughing and wheezing, and difficulty in breathing. Persons having attacks usually find it more difficult to exhale then inhale, which causes overinflation of the chest and impaired lung functions. The breathing difficulty is alleviated somewhat by