Asthma is a predisposition to chronic inflammation of the lungs in which the airways (bronchi) are reversibly narrowed. Asthma affects 7% of the population of the United States,[1][2] 6.5% of British people and a total of 300 million worldwide.[3] During asthma attacks (exacerbations of asthma), the smooth muscle cells in the bronchi constrict, the airways become inflamed and swollen, and breathing becomes difficult. This is often referred to as a tight chest and is a sign to immediately take medication.
Asthma causes 4,000 deaths a year in the United States. Medicines such as inhaled short-acting beta-2 agonists may be used to treat acute attacks. Attacks can also be prevented by avoiding triggering factors such as allergens or rapid temperature changes and through drug treatment such as inhaled corticosteroids and then long-acting beta-2 agonists if necessary.[4][5] Leukotriene antagonists are less effective than corticosteroids[citation needed], but have no side effects.[citation needed] Monoclonal antibodies, such as mepolizumab and omalizumab, are sometimes effective. Prognosis is good with treatment.
Although asthma is a chronic obstructive condition, it is not usually considered as a part of chronic obstructive pulmonary disease as this term refers specifically to combinations of bronchiectasis, chronic bronchitis, and emphysema. Unlike these diseases, the airway obstruction in asthma is usually reversible; however, if left untreated, asthma can result in chronic inflammation of the lungs and irreversible obstruction. In contrast to emphysema and bronchiectasis, asthma affects the bronchi, not the alveoli.[6] The National Heart, Lung and Blood Institute defines asthma as a common chronic disorder of the airways characterized by variable and recurring symptoms, airflow obstruction, bronchial hyperresponsiveness (bronchospasm), and an underlying inflammation.[7]
Public attention in the developed world has recently focused on the predisposition because of its rapidly increasing prevalence, affecting up to one quarter of urban children.[8]