Perception of dyspnea during acetylcholine-induced bronchoconstriction in asthmatic children

Background: Few studies have examined the relationship between dyspnea perception and bronchial hyperresponsiveness (BHR) in asthmatic children. Objective: To test the hypothesis that severe BHR is associated with poor perception of the severity of airway obstruction. Methods: One hundred one asthmatic children (mean [SD] age, 11.1 [2.3] years) were evaluated using acetylcholine chloride (Ach) challenge. The BHR was assessed as the provocative concentration of Ach causing a 20% decrease in forced expiratory volume in 1 second (FEV(1)) (PC(20)). Perception of dyspnea was scored using a modified Borg scale after each dose of Ach and bronchodilator. The dyspnea threshold was defined as the point at which the Borg scale score became higher than 0. We evaluated the dyspnea perception score at a 20% decrease in FEV(1) relative to baseline (PS(20)) and after bronchodilator administration (PS(BD)). Results: The mean (SD) PS(20) and PS(BD) were significantly lower in the severe vs the mild BHR group (PS(20): 2.1 [1.9] vs 4.2 [2.4], P < .001; PS(BD): 0.5 [1.0] vs 1.0 [1.3], P = .048). The mean (SD) % decrease in FEV(1) at the dyspnea threshold was significantly greater in the severe vs the mild BHR group (14.1% [11%] vs 5.4% [11%], P < .001). The PS(20) was correlated positively with the PC(20) (r(2) = 0.25, P < .004), and the decrease in FEV(1) at the dyspnea threshold was correlated negatively with the PC(20) (r(2) = 0.18, P < .001). Conclusions: Moderate to severe asthmatic children with severe BHR perceive dyspnea only after the stage of mild bronchoconstriction has passed. This relative insensitivity to dyspnea in asthmatic children with severe BHR may lead to undertreatment of asthma.