Asthma: new ideas about an old disease.

Asthma is a common and important disease, characterized by widespread bronchial obstruction that is reversible either spontaneously or with therapy. Its principal causes seem to be allergy, infections, irritants, and psychophysiologic reactions, usually in combinations. Induction of asthma by allergens is related to the presence of IgE antibodies fixed to mast cells and basophils. When these antibodies react with allergens, histamine and slow-reacting substance of anaphylaxis are released from the mast cells. There is also evidence of disturbance of control of the bronchi by the autonomic nervous system. Probably both increased cholinergic and decreased beta adrenergic effects are contributors. Some common manifestations of asthma have not been widely appreciated until recently. Hypoxia, due to altered ventilation-perf usion relationships, is nearly always present in severe asthma. Exercise-induced bronchospasm, of not yet completely understood origin, is a common problem for asthmatics and can usually be prevented by prophylactic administration of a bronchodilator.