Asthma is a chronic medical condition. It has been defined by the National Heart, Lung and Blood Institute as a common chronic disorder of the airways that is complex and characterized by variable and recurring symptoms, airflow obstruction, bronchial hyperresponsiveness (bronchospasm), and an underlying inflammation. The interaction of these features of asthma determines the clinical manifestations and severity of asthma and the response to treatment.
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.
Asthma is caused by a complex interaction of environmental and genetic factors that researchers do not yet fully understand. These factors can also influence how severe a person’s asthma is and how well they respond to medication. As with other complex diseases, many environmental and genetic factors have been suggested as causes of asthma, but not all studies posing such claims have been verified by further studies. In addition, as researchers detangle the complex causes of asthma, it is becoming more evident that certain environmental and genetic factors may affect asthma only when combined.
Because of the spectrum of severity within asthma, some asthmatics only rarely experience symptoms, usually in response to triggers, whereas 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.
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