Interrupter resistance (Rint) technique can be easily and successfully performed in preschool children. The establishment of Rint short-term repeatability is essential to interpret any Rint change after a pharmacological intervention.

In preschool children with asthma or chronic cough: (1) to assess two indices of short-term repeatability: (a) intra-measurement and (b) within-occasion between-test repeatability; (2) to study the relationship between short-term repeatability and bronchodilator response (BDR).

Rint intra-measurement repeatability assessed by the coefficient of variation was similar at baseline and after bronchodilator in asthmatics and in coughers (median 10% and 12%, respectively). There was no significant difference between asthmatics and coughers for both coefficient of repeatability (CR) (0.25kPaL⁻¹s and 32% of predicted vs 0.16kPaL⁻¹s and 21% of predicted, respectively) and BDR (median −14.7% vs −21.1% of predicted, respectively). However, in 20% of the study children, baseline variability of Rint modified the significance of the BDR.

In the present study, Rint short-term repeatability was similar to that of previous studies. Similar Rint repeatability in coughers and in asthmatic children favored the use of asthmatic CR for both populations, and a −35% cut-off as a positive BDR. In 20% of study children, baseline Rint variability could influence the significance of the BDR. In order to improve assessment of BDR using Rint, further studies are needed (1) to compare the variability of Rint to other resistance measurement techniques and (2) to define the best method for Rint calculation and for expression of BDR.