Asthma Is a Respiratory

Asthma 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 leaning forward and supporting the
trunk with the arms on some object. Attacks that
last several hours... [continues]

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