Increase in airway responsiveness and effect of deep inhalation on airway caliber in allergen-induced asthma. Relationship to the late-phase response.

The airway responsiveness to methacholine (MCh) and the effect of deep inhalation (DI) on airway caliber were determined in 18 asthmatic patients at baseline and 3 and 24 h after an allergen inhalation challenge. The dose of MCh causing a 20% fall of FEV1 (PD20) was used as an index of airway responsiveness; the ratio of forced expiratory flow at 40% of FVC from maximal and partial flow/volume curves (MEF40M/P) was used to assess the effect of DI on airway caliber. Thirteen patients showed a dual asthmatic response (DAR) to allergen, 5 patients an isolated early-phase asthmatic response (EAR). In the DAR patients, 3 h after allergen challenge, when the early-phase response had resolved and the late-phase response tied yet to develop, MChPD20 (geometric mean) was reduced from 202 to 71-mu-g (P < 0.001) whereas MEF40M/P at the MCh end point was unchanged (p > 0.4). Twenty-four hours after allergen challenge, when late-phase response had developed, MChPD20 was further reduced to 51-mu-g (p < 0.02), and this reduction was accompanied by a decrease of MEF40M/P at the MCh end point (p < 0.01) In the EAR patients, neither MChPD20 nor MEF40M/P was significantly changed at any time during the study. We conclude that most of the increase in airway responsiveness that follows acute exposure to allergen precedes the late-phase response and is not determined by the same mechanisms that impair the ability of the lung to dilate airways with a DI. We suggest that the early increase in airway responsiveness results from an Increased sensitivity of bronchial smooth muscle to constrictor stimuli, whereas the impairment of the ability of DI to increase airway caliber after the late-phase response reflects an Involvement of the lung periphery and/or edema of airways.