The interrupter technique to assess airway responsiveness in children with cystic fibrosis

The aim of this study was to assess the validity of the interrupter technique (R-int) in measuring airway responsiveness in children with cystic fibrosis. Fifty children (aged 6-16 years) with cystic fibrosis performed six R-int measurements followed by three acceptable forced expiratory maneuvers. Each child then inhaled 5 mg of nebulized salbutamol by facemask. After 20 min the R-int and forced expiratory measurements were repeated. In the population as a whole a moderate but significant correlation between inverse R-int and FEV1 values was observed, both before and after inhaled bronchodilator (r = 0.71 and 0.72, respectively P < 0.001). However, when changes in R-int and FEV1 readings following inhaled bronchodilator were examined, no relationship was seen. Indeed, the two methods identified completely different subsets of children as being bronchodilator responsive. These results indicate that although a relationship exists between R-int and FEV1 in the whole population, this is not the case in individual children. R-int and FEV1 reflect different aspects of lung function. It is not appropriate to use R-int as a simple alternative for FEV1 in children with cystic fibrosis when assessing airway responsiveness.