We compared the responses of cystic fibrosis (CF)(N = 14) and normal (N = 14) infants with inhaled methacholine. Airway function was assessed by forced expiratory flows at functional residual capacity (V̇max FRC) generated by the rapid compression technique, and methacholine responsiveness was quantitated as (1) TC: the threshold concentration to decrease V̇max FRC by 2 SD from baseline; (2) PC30: the provocative concentration to decrease V̇max FRC by 30%; and (3) SPC30: the slope of the dose-response curve between TC and PC30. There were no significant differences in age between CF and normal infants (16 ± 8 versus 17 ± 5 months, p > 0.3); however, the CF infants were shorter (74 ± 10 versus 81 ± 5 cm, p < 0.05), had lower absolute V̇max FRC (241 ± 103 versus 374 ± 113 ml/s, p < 0.001), and tended to have lower percentage of predicted flow values (87 ± 13 versus 111 ± 34%, p < 0.10). Comparison of the indices of airway responsiveness revealed no difference in logTC; however, the CF infants had smaller, more negative values for logPC30 (-0.76 ± 0.52 versus -0.22 ± 0.53, p < 0.02) and steeper slopes to their dose-response curves (logSPC30, 2.42 ± 0.45 versus 1.88 ± 0.74, p < 0.025). Indices of airway responsiveness correlated significantly with baseline V̇max FRC (% of predicted). After the influence of baseline flow upon airway responsiveness was accounted for by multiple linear regression analysis, there was a tendency for CF infants to be more responsive than control infants. We concluded that our infants with CF had heightened methacholine responsiveness compared with normal age-matched control infants; however, the difference in responsiveness was primarily related to CF infants having lower baseline flows.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine