Asthma is a breathing disorder characterized by narrowing of the airways (bronchoconstriction) and is accompanied by excessive mucous production. This causes obstruction of airflow resulting in difficulty breathing. The characteristic bronchoconstriction associated with asthma is episodic and reversible.
Asthma is common, affecting three percent of the U.S. population. It affects all ages but is most common in children under the age of ten. It more commonly affects males, and the incidence of asthma in the United States appears to be rising. Asthma accounts for a major expenditure of health care dollars.
The release of several chemicals, primarily histamine and a group of compounds known as leukotrienes cause the airway constriction in asthma. A variety of factors can stimulate the release of these chemicals, which prompted the classification of asthma into two types: extrinsic and intrinsic. Extrinsic asthma is allergic, or atopic. Here, bronchoconstriction is caused by the exposure to various allergens, such as pollens, animal fur, etc. In intrinsic asthma, the airway constriction is due to such things as exercise, respiratory illnesses, or emotional upset. The distinction between these two types of asthma is not made as much today, as the final pathway common to both types is the release of histamine and leukotrienes. The distinction is useful only as it allows for the identification of triggers to bronchoconstriction.
The diagnosis of asthma is made on the basis of history, a physical exam, and tests of lung function. The history should indicate that the breathing difficulty is episodic and reversible, rather than progressive. If not, diagnoses other than asthma should be considered. The history should also include the frequency, severity, and duration of the symptoms, as well as their impact on work, recreation, and sleep. An environmental history helps to identify allergic triggers to asthma attacks. Dietary and non-allergic triggers should be sought as well. The physical exam should focus on the respiratory tract and skin, looking for signs of allergy and atopy. A diagnostic study known as a pulmonary function test is recommended, both to help establish or confirm the diagnosis as well as to determine baseline lung function or degree of impairment. In some patients, X-Rays of the sinuses or chest are done to confirm the diagnosis of asthma, or to look for other conditions which can co-exist in asthmatics, such as sinusitis, nasal polyps, etc.