Assessment of bronchodilator response by airway resistance measurement using the interrupter resistance (Rint) technique in preschool children

Abstract

Estimation of the bronchodilator response (BDR) with spirometry in preschool children is not feasible due to poor cooperation in this age group.

The aim of this study was to assess accuracy of BDR estimated by Rint for asthma diagnosis in preschool children.

Material and methods

Expiratory Rint was measured in the group of asthmatic (doctor-diagnosed asthma) children (n=23; age=4,8±1,0 ys.; 82% boys) and control group (n= 15; age=4,6±0,7 ys.; 53% boys), before and after salbutamol (400ug using pMDI and spacer) inhalation, using Lung Test System (MES, Poland). BDR was expressed by the Rint change as percentage of predicted value. The predicted values were estimated by equations given by Merkus et al¹. Receiver operator characteristic (ROC) curves for BDR were generated to assess diagnostic performance of Rint for diagnosis of asthma.

Results

There were no significant differences in baseline Rint in asthmatic and control group, 0,92±0,24 versus 0,83±0,25 kPa^.L^-1.s (z-score: 0,54±1,14 versus 0,12±1,23) (p=0,29), and in intra-subject measurement variability (coefficient of variation-CV%) 9,8±2,9% versus 10,5±2,7% (p=0,48), respectively. BDR was significantly higher in asthmatic than in control group, 21,4±22,8% versus 6,1±14,9% (p=0,028), respectively. The diagnostic performance of BDR estimated by Rint (area under ROC curve = 0,719±0,084; p=0,009) revealed low sensitivity (56,5%) but high specificity (93,3%) on the level equal 21,6%.

Conclusion

BDR estimated by expiratory Rint allows to exclude asthma in preschool children with high accuracy.

¹Merkus PJFM, et al. Eur Respir J 2010;36:157–63.