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This study looked at the influence of inspired air water content on exercise-induced bronchospasm (EIB). On separate days, 12 mild asthmatics (4M, 8F), aged 18-39 yrs (mean: 27 yrs), performed four six minute steady-state exercises on ergometer at 80% of their maximum workload. Exercises were randomized to the following inspired air conditions: dry air (0% relative humidity (RH] during exercise followed by dry (DD) or humid air (100% RH) (DH) after exercise, humid air during exercise followed by dry (HD) or humid air (HH). Room temperature was kept constant (22 +/- 1 degree C) at all visits. Forced expiratory volume in one second (FEV1) was measured before and every 5 min for 25 min after exercise. Ventilation (VE) was not significantly different whether the exercise was done under dry or humid air. There was a residual bronchodilatation at the end of exercises performed in humid air, while at this time FEV1 was already lower than baseline when exercise was done in dry air conditions. The maximal fall in FEV1(%) following exercise was significantly greater after those performed in dry air: DD (29 +/- 5.6%) and DH (30 +/- 5.8%) than in humid air: HD (12 +/- 4.9%) and HH (20 +/- 4.9%) (p less than 0.05). The time-course of recovery from bronchoconstriction was significantly improved when inhaling dry air after exercise. However, the difference found in the maximal % fall in FEV1 after exercise when recovery was in dry compared to humid air did not achieve statistical significance. In conclusion, EIB is influenced by the changes in water content during and after exercise. Bronchoconstriction following exercise is minimal if exercise is done in humid air and recovery in dry air, and maximal if the exercise is performed in dry air and recovery in humid air.
Boulet et al. (Sun,) studied this question.