Asthma can be defined clinically as a condition of intermittent, reversible airway constriction, due to a hyperreactivity to certain substances producing inflammation .
In an asthma attack the smooth muscles of the lungs go into spasm with the surrounding tissue inflammed and secreting mucus into the airways. Thus, the diameter of the airways is reduced causing the characteristic wheezing as the person affected breathes harder to get air into the lungs. Attacks can vary in intensity and frequency.
Treatment for asthma includes the following drugs :

• Beta-adrenergic receptor agonists
• Anticholinergic drugs
• Theophylline
• Corticosteroids
• Leukotriene modifiers
• Cromolyn and Nedocromil . These two drugs are generally used to prevent an attack but are not so useful when treating an attack. They are relatively safe but expensive and need to be taken regularly, even when one is free of symptoms.

Asthma affects about 10 million Americans and seems to be on the increase (between 1982 and 1992 a 42% rise was recorded). Asthma can be divided into two principal types:

• Extrinsic Asthma
• Intrinsic Asthma