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The Pathophysiology of Asthma

written by: Rafael • edited by: Tania Cowling • updated: 10/10/2010

Asthma affects the function of the respiratory system. Learning the pathophysiology of asthma may be key to successfully managing the disease.

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    What Is Asthma?

    According to The Global Initiative for Asthma, as many as 300 million people suffer from this disease, with 10 million in the United States alone. Between 4,000-5,000 deaths in the U.S. are due to asthma attacks. Asthma is more common in children and young adults, but may occur anytime in life.

    Asthma can be defined as a chronic inflammatory disease of the respiratory system involving periodic and recurrent episodes of airflow obstruction and bronchospasm (sudden constriction of the muscles in the walls). Signs and symptoms of asthma (known as asthma attacks) include coughing, which usually worsens at nighttime, wheezing (defined as a high-pitched whistling sound when exhaling), difficulty breathing, shortness of breath, and chest tightness. Asthma episodes are reversible. Treatment of acute asthma is done with an inhaled, short-acting, beta-2 agonist such as Salbutamol. Prevention is key to avoiding asthma attacks, especially when the patient knows what triggers the asthma episode.

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    Pathophysiology of Asthma

    There are two types of asthma: extrinsic and intrinsic. With extrinsic asthma, the asthma episode is triggered by an inhaled irritant. It is basically an allergic reaction to an inhaled allergen. This type of asthma starts during childhood and improves as the person gets older. With intrinsic asthma, nonexternal stimuli trigger the asthma attack. A respiratory infection, stress, or exercise can trigger the asthma episode. Intrinsic asthma usually starts after age 30. The majority of patients experience a combination of both types of asthma.

    Bronchoconstriction and bronchial inflammation are two basic processes of the pathophysiology of asthma. In asthma patients, the bronchi and bronchioles are very responsive (hypersensitive) to irritants (allergens). A reaction to these irritants leads to swelling, inflammation, bronchoconstriction (contraction of the smooth muscle wall of the bronchi), and increased secretion of mucus by the respiratory airways.

    Upon breathing, allergen gets into the airways. These allergens are detected and bound to antigen presenting cells (APC). These APC cells "present" the allergen to other immune cells, which "check" the allergen. In nonasthmatic people, the allergen is ignored. But in asthma patients, these cells transform into TH2 cells, which activate the immunological system of the person. Antibodies against the inhaled allergen are generated and an immune response is manifested. This process produces inflammation with a reduction in bronchial airflow and bronchospasm. Asthma is also characterized by an increased number of eosinophils, neutrophils, lymphocytes, and plasma cells on the bronchial tissues, which also leads to immune-related reactions. The repeated cycles of inflammation of lungs and bronchi causes irreversible structural changes of the airways.

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    References:

    Fireman, P. 2003. Understanding asthma pathophysiology. Allergy Asthma. Proc. 4(2):79-83.

    Levy, M., Weller, T., Hilton, S. 2006. Asthma: The At Your Fingertips Guide. Class Publishing Ltd.

    GINA. The Global Initiative on Asthma. http://www.ginasthma.org/Reports.asp?l1=2&l2=1