Bronchial Hyperresponsiveness

One of the absolute features of asthma is exaggerated nonspecific airway reactivity to a variety of irritating stimuli. Thus, asthmatics develop airway obstruction in response to natural exposures (cold air, exercise, irritating chemicals, laughing, and coughing) or to provocations in the laboratory (histamine, methacholine, cold air hyperventilation) (Table 9). Airway hyperresponsiveness is found universally in asthmatics, in a portion of subjects with chronic bronchitis, in some subjects with allergic rhinitis, and in 3-8% of otherwise normal subjects. There is a close correlation between the degree of increased responsiveness and disease severity: patients with the most reactive airways often require oral CCSs for control, whereas milder degrees of abnormality predict the requirement for fewer medications. Hyperresponsiveness increases after allergen exposure, late-phase allergic reactions, viral infections (especially influenza-type infections), and ozone exposure. Conversely, airway hyperresponsiveness may return toward normal after allergen avoidance, allergy immunotherapy, or treatment with cromolyn or inhaled or oral CCS. In recent years, airway hyperresponsiveness and airway inflammation have become prime targets in asthma therapy, leading to the use of anti-inflammatory agents to reduce airway reactivity.

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