Response to inhaled bronchodilators and nonspecific airway hyperreactivity in children with cystic fibrosis

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Abstract
We tested the hypothesis that children with CF who have a significant response to bronchodilator (ED) would respond positively to standard methacholine (Mch) challenge. Our objective was to correlate the response to BD with the concentration that produced a 20% fall (PC20) in forced expiratory volume in 1 second (FEV1). We studied 22 patients (12 males), aged 10.5 ± 0.7 years (mean ± SE), with a Shwachman‐Kulczycki score 82 ± 2.6 and baseline FEV11 of 80 ± 4.5% predicted. Baseline expiratory flows, static lung volumes, and airway resistance were measured before and 30 min after inhaled salbutamol. On a separate day, within 2 weeks, a Mch challenge was given, with doubling concentrations from 0.03 to 8.0 mg/mL. A positive challenge was defined as a PC20≦ 2.0 mg/mL, and a positive response to BD as a >6%0 of FEV1 increase. Mch challenge yielded 17 responders (R) with a PC20 of 0.5 ± 0.1 mg/mL, and 5 nonresponders (NR) with a PC20 of 8.8 of 2.9 mg/mL. Baseline FEV11 was 77 ± 5.3% predicted in R compared to 89 ± 6.3% in NR (P = < 0.001). History of springtime rhinitis was positive in 9/17 R and 2/5 NR. No significant correlation was found between baseline FEV1 1 and PC20 or between change in FEV1 1 post‐BD and PC20 A >6% increase in FEV1 1 was seen in 14/17 R (83% sensitivity) and in none of the 5 NR (100% specificity). In R, 8/17 patients had baseline FEV1 1 < 80% predicted, compared to 1/5 in NR. We conclude that a change in FEV11 > 6% from baseline after bronchodilator in children with CF suggests nonspecific airway hyperreactivity.