The bronchoprotective effect of deep inspiration is flow rate dependent

SummaryBackground and study objectiveDeep inspiration (DI) protects against methacholine-induced bronchoconstriction in healthy subjects. We hypothesized that this bronchoprotective effect of DI depends upon the inspiratory flow rate.DesignProspective, controlled study.SettingPulmonary function laboratory within a large tertiary medical center.ParticipantsTen healthy nonsmokers without asthma or rhinitis.MeasurementsFirst, we performed a methacholine challenge in the absence of DI to determine the concentration sufficient to reduce FEV1 by 20%. On two subsequent days, the challenge was repeated with the addition of either a fast or slow DI immediately before the threshold concentration of methacholine. We calculated the % reduction in FEV1 and FVC from baseline.ResultsMean % reduction in FEV1 and FVC was significantly less with a fast DI than with no DI (20±3% vs. 34±4% for FEV1, p=0.02; 12±3% vs. 23±3% for FVC, p=0.03); slow DIs did not significantly affect the methacholine-induced reduction in lung function.ConclusionA fast DI is bronchoprotective while a slow DI is not. Elucidating the conditions that maximize or alternatively, eliminate bronchoprotection in healthy subjects may ultimately provide insight into the pathophysiology of asthma.