The bronchoprotective effect of deep inspiration is flow rate dependent.

Summary Background and study objective Deep inspiration (DI) protects against methacholine-induced bronchoconstriction in healthy subjects. We hypothesized that this bronchoprotective effect of DI depends upon the inspiratory flow rate. Design Prospective, controlled study. Setting Pulmonary function laboratory within a large tertiary medical center. Participants Ten healthy nonsmokers without asthma or rhinitis. Measurements First, we performed a methacholine challenge in the absence of DI to determine the concentration sufficient to reduce FEV 1 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 FEV 1 and FVC from baseline. Results Mean % reduction in FEV 1 and FVC was significantly less with a fast DI than with no DI (20±3% vs. 34±4% for FEV 1 , 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. Conclusion A 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.