Comparisons of specific and nonspecific bronchoprovocation in subjects with asthma, rhinitis, and healthy subjects

We studied subjects with atopic asthma, atopic rhinitis, and nonatopic healthy subjects to evaluate responsiveness to bronchoprovocation with both methacholine and allergen. Subjects with a demonstrable FEV1 PD20 to methacholine or allergen (responders) were further analyzed for putative sensitivity (PD20 FEV1) and reactivity (dose-response slopes) to determine whether any characteristics could distinguish individuals with asthma from other responders. Subjects were recruited without sex restrictions and were between the ages of 18 and 45 years old. They were nonsmokers, had no other medical problems, and were free of upper respiratory infection for at least 6 weeks before challenge. All had a history taken, physical examination, limited laboratory screening, chest radiography, pulmonary function testing, and intradermal skin testing before admission to the study. Although the groups were significantly different in both sensitivity and reactivity to methacholine, responses to allergen bronchoprovocation were sufficiently similar between responders with asthma and those with rhinitis to prevent separation on the basis of either sensitivity or reactivity. The fall in FEV1 at the nadir of the late response, which was greater in the asthma group, was significantly correlated with sensitivity and reactivity of the immediate response to allergen but not to methacholine. Regression analysis demonstrated a stronger association between allergen and methacholine responsiveness in subjects with rhinitis than in subjects with asthma. We concluded that (1) nonspecific bronchial hyperresponsiveness fails to explain why patients with allergic asthma have clinical asthma as a result of allergen exposure and patients with allergic rhinitis do not; (2) hyperresponsiveness to allergen does not simply reflect quantitative or qualitative airway nonspecific hyperresponsiveness; and (3) clinical asthma may involve mechanisms difficult to elucidate by laboratory bronchoprovocation techniques.