Induction and recovery phases of methacholine-induced bronchoconstriction using FEV1 according to the degree of bronchial hyperresponsiveness.

Forty-eight patients suffering from intermittent bronchial asthma underwent methacholine challenge test. Response was stronger in 29 patients and less pronounced in 19. The two groups had the same characteristics except for the cumulative methacholine dose which was lower in severe hyperresponsiveness. The patients were studied both in the phase of induced bronchospasm and in the subsequent phase of spontaneous recovery. Dose-response curves to methacholine were analyzed as FEV1% decline/methacholine dose for the induction phase of bronchoconstriction and as FEV1% increase*methacholine dose/time after PD20FEV1 for the recovery phase. The phase of induced bronchospasm as well as spontaneous recovery had a linear pattern in severe hyperresponsiveness; in patients with moderate response, induced bronchoconstriction had a curvilinear pattern whereas spontaneous recovery had a linear pattern. This latter group had to break down an amount of methacholine that was fivefold greater than the former, therefore the mechanism of local homeostasis recovery may be more efficient in moderate hyperresponsiveness. However, in both groups recovery after the bronchospasm was not complete after 60 min (p < 0.01 versus baseline). Furthermore, recovery was faster in the first 15 min than in the remaining time. In conclusion the behavior of methacholine-induced bronchospasm and its spontaneous recovery in both severe and moderate hyperresponsiveness seem to be different although several and not well-established mechanisms may be responsible for this phenomenon.