ABSTRACT
Asthma is a chronic disease characterised by increased responsiveness of the tracheobronchial tree to various stimuli (e.g. inhaled allergens, infection, exercise, anxiety, cold or drugs). It manifests as widespread airway narrowing with mucosal oedema and a cellular infiltrate. Reversibility of airway obstruction is characteristic and distinguishes asthma from the fixed obstruction of chronic bronchitis and emphysema. The severity of airflow obstruction varies widely over short periods but airway resistance may be normal for long periods. Acute severe asthma may be a life-threatening condition, especially when combined with one or more adverse psychosocial factors (psychiatric illness, alcohol or drug ingestion, unemployment, etc.).
