Asthma

Asthma is a chronic inflammation of the lungs in which the airways (bronchi) are reversibly narrowed. Asthma affects 7% of the population, or 20 million Americans,[1][2] and 300 million worldwide.[3] During attacks (exacerbations), the smooth muscle cells in the bronchi constrict, and the airways become inflamed and swollen. Breathing becomes difficult, and asthma causes 4,000 deaths a year in the U.S. Attacks can be prevented by avoiding triggering factors and by drug treatment. Drugs are used for acute attacks, commonly inhaled β2-agonists. In more serious cases, drugs are used for long-term prevention, starting with inhaled corticosteroids, and then long-acting β2-agonists if necessary. Leukotriene antagonists are less effective than corticosteroids but have no side effects. Monoclonal antibodies such as mepolizumab and omalizumab are sometimes effective. Prognosis is good with treatment.

In contrast to chronic obstructive pulmonary disease and chronic bronchitis, the inflammation of asthma is reversable. In contrast to emphysema, asthma affects the bronchi, not the alveoli.

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.[4]

Public attention in the developed world has recently focused on asthma because of its rapidly increasing prevalence, affecting up to one in four urban children.
Classification

Signs and symptoms

Because of the spectrum of severity within asthma, some asthmatics only rarely experience symptoms, usually in response to triggers, where as other more severe asthmatics may have marked airflow obstruction at all times.

Asthma exists in two states: the steady-state of chronic asthma, and the acute state of an acute asthma exacerbation. The symptoms are different depending on what state the asthmatic is in.

Common symptoms of asthma in a steady-state include: nighttime coughing, shortness of breath with exertion but no dyspnea at rest, a chronic 'throat-clearing' type cough, and complaints of a tight feeling in the chest. Severity often correlates to an increase in symptoms. Symptoms can worsen gradually and rather insidiously, up to the point of an acute exacerbation of asthma. It is a common misconception that all asthmatics wheeze—some asthmatics never wheeze, and their disease may be confused with another Chronic obstructive pulmonary disease such as emphysema or chronic bronchitis.

An acute exacerbation of asthma is commonly referred to as an asthma attack. The cardinal symptoms of an attack are shortness of breath (dyspnea), wheezing and chest tightness.[7] Although the former is "often regarded as the sine qua non of asthma.[8] some patients present primarily with coughing, and in the late stages of an attack, air motion may be so impaired that no wheezing may be heard.[9].When present the cough may sometimes produce clear sputum. The onset may be sudden, with a sense of constriction in the chest, breathing becomes difficult, and wheezing occurs (primarily upon expiration, but can be in both respiratory phases). It is important to note inspiratory stridor without expiratory wheeze however, as an upper airway obstruction may manifest with symptoms similar to an acute exacerbation of asthma, with stridor instead of wheezing, and will remain unresponsive to bronchodilators.