The Effect of Pre-Exposure to 0.12 ppm of Ozone on Exercise-Induced Asthma: Conclusion

Consistent with this is our previous observation13 that there was no associated increase in methacholine responsiveness after allergen challenge despite an increase in allergen responsiveness after ozone exposure of 0.12 ppm at rest for 1 h.
Broide et al23 suggested that the cellular pathogenesis of exercise-induced asthma (mast cell independent) differs from current theories of the pathogenesis of extrinsic allergen induced asthma (mast cell dependent). While ozone and allergen-induced airway hyperresponsiveness share some similar features suggesting that the underlying mechanism may share a common pathway as shown by Molfino et al, we could not demonstrate a similar relationship between ozone and exercise-induced asthma.
There are differences between individuals in the susceptibility to ozone-induced hyperresponsiveness even using higher exposure levels.3 It is interesting to note that patient 15 had a significant decrease in FEVi and V40P after ozone chamber exposure alone (15% fall), before the exercise performance. As his baseline values were at 100 percent of his predicted, it permitted us to have him perform an exercise challenge and remain within our previous criteria of FEVi >70 percent pre-exercise. After exercise he did not show an additional drop in his lung function parameters suggesting that the previous bronchocon-triction induced a refractoriness or protection to exercise. As this was only a single observation, it is difficult to draw any defensive conclusions regarding the susceptibility to ozone exposure and subsequent exercise challenge. With repeated exposure to high concentrations of ozone, induced changes become progressively smaller; this acquired resistance to the effects of ozone has been described as “tachyphylaxis.”’ asthma medications inhalers

Differences observed in a sequence of provocative events seem to be related to the liberation of mediators. In bronchoalveolar lavage of subjects exposed to 0.08 ppm of ozone, Devlin et al7 observed an increase in PGE2 which we could speculate may play a role in blocking a muscle contraction subsequent to a further stimulus like exercise.

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