Effect of deep inspiration on airway caliber in children with asthma

The objective of this study was to assess the effect of deep inspiration (DI) on airway caliber in school-age children with asthma. Thirty children with asthma (10 from each group of mild, moderate, and severe persistent asthma as defined by the National Asthma Education and Prevention Program guidelines of the National Heart, Lung, and Blood Institute) were enrolled, and their results were compared to those obtained in 7 healthy children. Subjects performed a partial expiratory flow volume curve (P) initiated from similar to70% of vital capacity (VC) followed by a maximal expiratory flow volume (M) maneuver begun from total lung capacity (TLC). The M/P ratio at 30% of the VC (M/P-30) was calculated. Specific airway conductance (sG(aw)) was measured before and immediately after DI, using standard techniques. Differences in M/P-30 and sGaw ratios between asthma and control groups were compared with Student's unpaired t-tests. One-way ANOVA was used to compare the effect of DI on M/P-30 and sGaw ratios among the various asthma severity groups. The M/P-30 ratio (mean +/- 1 SD) was significantly lower in children with moderate and severe persistent asthma (0.73 +/- 0.21 and 0.72 +/- 0.1, respectively) than in healthy controls (1.69 +/- 0.62) (P<0.05). In mild persistent asthmatics, there was limited bronchodilation (M/ P-30=1.1 +/- 0.35, P=0.052). There was a significant inverse correlation between M/P-30 ratio and severity of asthma (r=-0.684, P<0.01). The mean sGaw ratio was decreased in asthmatic subjects compared to healthy controls (0.98 +/- 0.17 vs. 1.13 +/- 0.16, P=0.062). In conclusion, in school-age children, the effects of DI on airway caliber are similar in direction to those observed in adults, i.e., bronchodilation in healthy and mild asthmatics, and bronchoconstriction (BC) in moderate to severe asthmatics. This finding suggests that forces that determine airway caliber in school-age children are similar to those forces in adults. (C) 2004 Wiley-Liss, Inc.