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FOUNDATION OVERVIEW

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The characteristics of asthma are airway inflammation and bronchial hyperresponsiveness which cause variable degree of airflow obstruction. In the asthmatic response, a genetically predisposed or atopic individual is exposed to a specific reactive stimulus or trigger. Common asthma triggers include mold, pollen, animal dander, and dust mites. Minutes after repeated exposure, the immediate asthmatic response occurs causing bronchoconstriction which resolves spontaneously or easily by β2-agonist use. Within 4 to 12 hours after the immediate asthmatic response, the late asthmatic response, caused by influx of inflammatory cells primarily eosinophils, Th2 lymphocytes, mast cells, macrophages, and mediators such as leukotrienes, histamine, and prostaglandin infiltrate the airway. The reaction is often severe and prolonged and is referred to as an asthma exacerbation. This chronic inflammation is postulated to cause hypertrophy and hyperplasia of the bronchial smooth muscle and mucus glands which may lead to permanent, irreversible obstruction termed airway remodeling. The combination of airway obstruction and inflammation leads to the common symptoms of asthma which are cough (especially one that wakes the patient at night), wheezing, chest tightness, and dyspnea. In the pediatric population males are twice as likely to be diagnosed with asthma; however, this ratio equals between males and females in adulthood.

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Diagnosis is based on a thorough history with special focus on symptoms and genetic predisposition. Spirometry is the initial test used to diagnose asthma. This is a diagnostic test where a person exhales forcefully into a machine to determine if airflow obstruction is present. To determine if obstruction is present, the ratio of the forced expiratory volume in 1 second (FEV1) over forced vital capacity (FVC) is reviewed (Table 45-1). To determine reversibility, as in asthma, a short-acting β-agonist (albuterol) is given and the postbronchodilator FEV1 is evaluated. If the FEV1 improves 12% or more and 200 mL when compared to prebronchodilator value, the person is diagnosed with asthma. Once diagnosis is made, further age-specific evaluation based on impairment and risk is determined in order to classify severity and control of asthma (Tables 45-1 and 45-2). A person is assigned to the highest step based on the most severe sign or symptom and once control has been maintained for at least 3 months, therapy is stepped down.

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TABLE 45-1Asthma Severity Classification

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