Do exercise- and antigen-induced asthma utilize the same pathways? Antigen provocation in patients rendered refractory to exercise-induced asthma.

Twelve asthmatics (ages 8 to 33 yr) with proven exercise-induced asthma (EIA) and allergen-induced asthma (AIA) were investigated in an attempt to elucidate the pathways through which each type of attack develops. All patients were rendered refractory to EIA by repeated exercise at short intervals and were then immediately challenged by inhalation with an allergen known to evoke AIA. After an average of three runs all subjects were rendered refractory to EIA (post-exercise fall in FEV1 of 7 +/- 8% SEM compared with the control postexercise fall of 32 +/- 14%). In this refractory state six patients failed to respond to antigen challenge (6 +/- 4% SEM fall in FEV1 compared with the 30 +/- 3% fall in control study, p less than 0.001), suggesting a common pathway for EIA and AIA, such as the exhaustion of stored chemical mediators. Six other patients developed attacks of AIA while refractory to EIA, which were at least as severe as those in their control study (34 +/- 7% SEM fall in FEV1 compared with 29 +/- 3%). The fact that AIA could develop while EIA was blocked in this group requires an alternate pathway or mechanism for their AIA. The only significant difference between the AIA "blocked" and AIA "nonblocked" groups was a lower baseline level of lung function in all tests in the nonblocked group.