A Bronchial Response Comparison of Exercise and Methacholine in Asthmatic Subjects

The authors compared the inhaled methacholine and exercise responses in 22 stable unmedicated asthmatic patients. The exercise and methacholine challenges were performed at one to three week intervals. Bronchial responsiveness to methacholine was measured in relation to the concentration of methacholine (PC₂₀M). The response to exercise was expressed as the percentage of fall in FEV₁, from the pre-exercise FEV₁ The findings showed that 21 of 22 subjects demonstrated a fall in FEV₁, of more than 20% after methacholine challenge, while only 9/22 subjects experienced a similar decrease in FEV₁. All 9 of these positive response exercise cases completed three consecutive exercise challenges prior to the methacholine challenge. Of these cases, five were refractory to the repeated exercise challenge, and the PD₂₀M at the nonexercise stage was significantly lower than the postexercise state. In fact, the methacholine challenge sensitivity actually decreased (PD₂₀ increased) after repeated exercise. The authors concluded that methacholine seems to be a more sensitive bronchial provocation test than exercise. Second, only 55.6% of the exercise test-positive subjects were refractory to the second exercise challenge. Therefore, other factors besides the release of mediators should be considered in exercise induced asthma. Third, methacholine sensitivity actually decreased (PD₂₀ increases) after repeat exercise challenge.