Within-breath resistance and reactance and short-term repeatability in two forced oscillation technique devices

Introduction: The forced oscillation technique (FOT) is gaining clinical importance as a lung function test with the increasing availability of commercial devices. Device comparisons have been made but not in within-breath parameters. Aim: To compare total, inspiratory and expiratory resistance (Rrs) and reactance (Xrs) between two commercial FOT devices. Methods: 12 healthy subjects performed 3 sets of tidal breathing measurements on both devices (tremoFlo C-100 (Thorasys Medical Systems, Canada) and Resmon Pro (Restech, Italy)) in random order. Measurements were repeated after 15 min and the coefficient of repeatability (CoR) calculated. We compared total, inspiratory and expiratory Rrs and Xrs at 5 Hz from within-breath analysis (paired t-tests), expressed as raw and predicted values (Oostveen et al, 2013). We also examined test objects of known Rrs and Xrs. Results: Subjects (7 males) had mean±SD age 33±11 years, height 170±7 cm, and weight 67.3±8.8 kg. PredFEV1 and FVC were 95±13% and 98±12% respectively. No significant differences in total, insp or exp Rrs were seen. Xrs values were less negative (P<0.05) for Resmon Pro, and insp-exp Xrs was greater for tremoFlo (-0.25±0.14 vs -0.02±0.14, P=0.0007). CoR for Rrs and Xrs were 0.43 and 0.23 for tremoFlo and 0.39 and 0.24 for Resmon Pro respectively. No differences were seen in test objects. Conclusions: The tremoFlo and Resmon Pro measure similar Rrs and short-term repeatability. There is disparity in Xrs in subjects but not in test objects.