Measurement of airway resistance using the interrupter technique (Rint) in preschool children with bronchopulmonary dysplasia in ambulatory setting

Background: Measurement of airway resistance by interrupter technique (Rint) is feasible in preschool children unable to undertake spirometry. Though normative data have been established in healthy 2-10 year old children the value of Rint for children with chronic illness has not been established. Premature infants surviving with bronchopulmonary dysplasia (BPD) are reported to have abnormal lung function in childhood. We therefore aimed to determine the sensitivity of MicroRint (Micro Medical Ltd, Rochester, UK), a portable device, to identify differences in Rint in preschool children with BPD compared to preterm controls and its feasibility in an outpatient setting. Method: Rint was measured by a single investigator using a standard technique in 76 eligible children between 2-5 yrs old attending outpatients. The mean of at least 6 acceptable values of Rint with consistent shape of pressure waveform (Pmo(t)) was taken. Children with respiratory illness within 1 month, congenital anomaly and cardiac defects were excluded. Results: Rint was measured successfully in 10/28 (36%) 2-3 yr, 13/20 (65%) 3-4 yr and 23/28 (82%) 4-5 yr old children (n=76, 26 BPD and 20 Controls). There was no difference in Rint between BPD and preterm control children (n=46, median 1.36 v 1.22 kPa/l.s, p=0.64) Conclusions: Although measuring Rint is feasible in preschool children in an ambulatory set-up, Rint is not increased in preschool children with BPD compared to preterm controls.