Definition and Pathophysiology
Asthma is a reversible airways disease characterized by both smooth muscle hyperreactivity and airway inflammation. During the 1970s and early 1980s the focus was on smooth muscle constriction, and it was believed that better bronchodilators would greatly diminish our difficulties in controlling this condition. This, unfortunately, was not the case. The emphasis of therapy today has turned to airway inflammation. Lung biopsies from patients who have asthma show destruction of respiratory epithelium, basement membrane thickening, and inflammatory cellular infiltrate. Among the infiltrating cells are eosinophils, macrophages, and neutrophils that are called to the site of inflammation by the chemotactic products released by activated mast cells. Upon their arrival, these cells release their own products of inflammation, which amplify this immunologic response. A variety of neuropeptides also play a role, some serving to stabilize and others to destabilize the airway. One result of this airway inflammation is airways reactivity, also known as bronchial hyperresponsiveness.
A common example of this scenario is the child who has allergic asthma and encounters a problematic allergen. This child has immunoglobulin E (IgE) to this allergen bound to mast cells in his or her airway. Upon exposure to the allergen, the binding of IgE and antigen triggers mast cell mediator release within minutes.
1704 RUNNING IMPROVES FITNESS IN ASTHMATIC CHILDREN WITHOUT CHANGING AIRWAYS REACTIVITY OR VENTILATORY MUSCLE FUNCTION
