The lack of the bronchoprotective and not the bronchodilatory ability of deep inspiration is associated with airway hyperresponsiveness

In healthy subjects, deep inspiration (DI) acts both as a bronchodilator an d a bronchoprotector. The latter is impaired in asthmatics. We have now eva luated whether the lack of bronchoprotection is related to bronchial hyperr esponsiveness (BHR), and whether the bronchodilatory effect is also lost in asthmatics, Ten healthy subjects (PC20 > 75 mg/ml), 12 asthmatics with mod erate to severe BHR (PC20 < 1 mg/ml), 14 asthmatics with mild to borderline BHR (1 < PC20 < 25 mg/ml), and 10 rhinitics with mild to borderline BHR (1 < PC20 < 25 mg/ml) underwent single-dose methacholine provocations inducin g at least 20% reduction in FEV1 after 20 min of DI inhibition. To measure the bronchodilatory effect, DIs were taken immediately after the postmethac holine spirometry, and lung function was again tested. To measure the bronc hoprotective effect, Dls were taken before the administration of spasmogen. All four groups achieved the same reductions in FEV1 and FVC, in the absen ce of deep breaths (analysis of variance [ANOVA], p = 0.49). Only healthy s ubjects showed bronchoprotection (percent bronchoprotection, mean +/- SEM; healthy: 79 +/- 4.0; asthmatics with moderate to severe BHR: 12 +/- 14.5; a sthmatics with mild to borderline BHR: -7 +/- 19.7; rhinitics with mild to borderline BHR: 2 +/- 14.0). In contrast, Dls were able to partially revers e bronchial obstruction in all four groups, albeit percent bronchodilation in healthy subjects was somewhat stronger. The dissociation between broncho protection and bronchodilation suggests that the two effects involve differ ent mechanisms.