The bronchoprotective effect of deep inspiration is flow rate dependent

Abstract

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. Prospective, controlled study. Pulmonary function laboratory within a large tertiary medical center. Ten healthy nonsmokers without asthma or rhinitis. 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. 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. 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.