Comparison between within-test and triplicate recordings of impedance by forced oscillation technique (FOT)

Background: Current ERS recommendations suggest recording 3-5 acceptable FOT tests to measure a subject’s resistance (Rrs) and reactance (Xrs). A different approach that evaluates Rrs and Xrs during 10-15 breaths from a single test, excludes breaths with artefacts and calculates Rrs and Xrs as the mean value of the accepted breaths has been introduced. However, no data is available to support the equivalence between the methods. Aim: To assess the impact of using an increasing number of complete breaths without artefacts for calculating Rrs and Xrs as compared with the method recommended by ERS in healthy children. Methods: 155 subjects (8.3±2.1 years old) without a history of asthma, wheezing or systemic diseases were recruited in primary schools. 3 FOT tests of 10-15 breaths each were performed using the Resmon PRO FULL (Restech, Italy). Rrs and Xrs were computed at 5Hz for each test using the cross-spectrum method and results were averaged as per ERS recommendations. For the first test, Rrs and Xrs were also computed as the average of the first 3, 4, 5, 7 and 10 full free-from-artefacts breaths. Differences were tested by ANOVA for repeated measurements. Results: Significant differences between the methods were found only for Xrs (Figure) and associated with a higher within-breath variation of this parameter. Conclusions: Rrs can be reliably calculated by the within-breath method from a single FOT test.