Within-session variability as quality control for oscillometry in health and disease

Oscillometry is increasingly adopted in respiratory clinics, however many recommendations regarding measurement settings and quality control remain subjective. The aim of this study was to investigate the optimal number of measurements and acceptable within-session coefficient of variation (CoV) in health, asthma and COPD. Fifteen healthy, 15 asthma and 15 COPD adult participants were recruited. Eight consecutive 30 s measurements were made using an oscillometry device (tremoFlo C-100, Thorays Thoracic Medical Systems Inc., Canada) from which resistance at 5 Hz (Rrs5) was examined. The effect of progressively including a greater number of measurements on Rrs5 and its within-session coefficient of variation (CoV) was investigated. Data was analysed using one-way repeated measures ANOVA with Bonferroni post-hoc test. The CoV(Rrs5) of the first 3 measurements was 6.7±4.7%, 9.7±5.7%, and 12.6±11.2% in healthy, asthma and COPD participants, respectively. Both mean Rrs5 and CoV(Rrs5) were not statistically different when progressively including 4–8 measurements. Selecting the 3 closest Rrs5 values over an increasing number of measurements progressively decreased the CoV(Rrs5). In order for ≥95% of participants to fall within a target CoV(Rrs5) of 10%, ≥4, 5 and 6 measurements were needed in health, asthma, and COPD, respectively. Within-session variability of oscillometry is increased in disease. Furthermore, the higher number of measurements required to achieve a set target for asthma and COPD patients may not be practical in a clinical setting. Provided technical acceptability of measurements is established, i.e. by removing artefacts and outliers, then a CoV of 10% is a marker of quality in most patients, but we suggest higher CoVs upto 15–20% should still be reportable.