Measurement duration impacts variability but not impedance measured by the forced oscillation technique in healthy, asthma and COPD subjects

The forced oscillation technique (FOT) is gaining clinical acceptance, facilitated by more commercial devices and clinical data. However, the effects of variations in testing protocols used in FOT data acquisition are unknown. We describe the effect of duration of data acquisition on FOT results in subjects with asthma, chronic obstructive pulmonary disease (COPD) and healthy controls. FOT data were acquired from 20 healthy, 22 asthmatic and 18 COPD subjects for 60 s in triplicate. The first 16, 30 and 60 s of each measurement were analysed to obtain total, inspiratory and expiratory resistance of respiratory system (R(rs)) and respiratory system reactance (X(rs)) at 5 and 19 Hz. With increasing duration, there was a decrease in total and expiratory R(rs) for healthy controls, total and inspiratory R(rs) for asthmatic subjects and magnitude of total and inspiratory X(rs) for COPD subjects at 5 Hz. These decreases were small compared to the differences between clinical groups. Measuring for 16, 30 and 60 s provided ≥3 acceptable breaths in at least 90, 95 and 100% of subjects, respectively. The coefficient of variation for total R(rs) and X(rs) also decreased with duration. Similar results were found for R(rs) and X(rs) at 19 Hz. FOT results are statistically, but likely minimally, impacted by acquisition duration in healthy, asthmatic or COPD subjects.