Exercise-induced bronchodilation in natural and induced asthma: effects on ventilatory response and performance

We studied whether bronchodilatation occurs with exercise during the late asthmatic reaction (LAR) to allergen (group 1, n=13) or natural asthma (NA; group 2, n=8) and whether this is sufficient to preserve maximum ventilation ((V)over dot(Emax)), oxygen consumption ((V)over dotO(2 max)), and exercise performance ((W)over dot(max)). In group 1, partial forced expiratory flow at 30% of resting forced vital capacity increased during exercise, both at control and LAR. (W)over dot(max) was slightly reduced at LAR, whereas (V)over dot(Emax), tidal volume, breathing frequency, and (V)over dotO(2 max) were preserved. Functional residual capacity and end-inspiratory lung volume were significantly larger at LAR than at control. In group 2, partial forced expiratory flow at 30% of resting forced vital capacity increased greatly with exercise during NA but did not attain control values after appropriate therapy. Compared with control, (W)over dot(max) was slightly less during NA, whereas (V)over dotO(2 max) and (V)over dot(Emax) were similar. Functional residual capacity, but not end-inspiratory lung volume at maximum load, was significantly greater than at control, whereas tidal volume decreased and breathing frequency increased. In conclusion, remarkable exercise bronchodilation occurs during either LAR or NA and allows (V)over dot(Emax) and (V)over dotO(2) max to be preserved with small changes in breathing pattern and a slight reduction in (W)over dot(max).