Objective: To determine and validate a cut-off value for bronchodilation using the interrupter resistance (Rint) in preschool children.
Patients and methods: Rint was measured in 60 healthy children (age range 2.7-6.4 years) before and after salbutamol inhalation (200 microg). Four potential methods for assessing BDR were evaluated: percent change from baseline, percent change of predicted values, absolute change in Rint, and change in Z-score. These cut-off values, determined as the fifth percentile of the healthy group, were applied to children referred for the assessment of recurrent wheezing, classified on the basis of acute symptoms and/or abnormal chest examination into symptomatic (n = 60, age range 2.9-6.1 years) and asymptomatic (n = 60, age range 2.5-5.7 years) groups.
Results: The cut-off values for bronchodilation calculated in healthy children were: -32% baseline; -33% predicted; -0.26 kPa L(-1) sec; and -1.25 Z-scores. Assessing BDR in children with a history of wheezing by either a decrease in absolute Rint or a decrease in Z-score gave sensitivity, specificity, negative predictive value, and positive predictive value all >80% for detecting children with current respiratory symptoms.
Conclusions: Both a decrease in Rint > or =0.26 kPa L(-1) sec and a decrease in Z-score of > or =1.25 are appropriate for assessing BDR in preschool children with a history of recurrent wheezing. As Z-score is a more general solution, we recommend using a change in Z-score to determine BDR in preschool children. Further longitudinal studies will be required to determine the clinical utility of measuring BDR in managing lung disease in such children.