Day-to-day variability of forced oscillatory mechanics for early detection of acute exacerbations in COPD.

BACKGROUND: Telemonitoring trials for early detection of acute exacerbations (AECOPD) have provided mixed results. Day-to-day variations in lung function measured by forced oscillation technique (FOT) may yield better insight. We evaluated the clinical utility of home telemonitoring of variability of FOT measures, in terms of (i) relationship with symptoms and quality of life, and (ii) the timing of variability of FOT measures and symptom changes prior to AECOPD. METHODS: Daily FOT parameters at 5 Hz (resistance (R) and reactance (X); Resmon Pro Diary, Restech Srl), daily symptoms (COPD Assessment Test, CAT) and 4-weekly quality of life (St. George's Respiratory Questionnaire, SGRQ) were obtained over 8-9 months from COPD patients. Variability of resistance and reactance was calculated as the standard deviation (sd) over 7-day running windows; we also examined the effect of varying window size. The relationships between FOT versus CAT and SGRQ were assessed using linear mixed modelling, daily changes in FOT variability and CAT prior to AECOPD using one-way repeated measures ANOVA. RESULTS: 15 participants with mean(sd) age 69(10) years and FEV1%predicted 39(10) had a median(IQR) adherence of 95.4(79.0-98.8)%. Variability of the inspiratory component of X (SDXinsp) related to CAT and weakly SGRQ (fixed effect estimate(95%CI) 1.57(0.65-2.49), p=0.001 and 4.41(-0.06-8.89), p=0.05, respectively). SDXinsp changed significantly on the same day as CAT (1 day before AECOPD, both p=0.02), and earlier when using shorter running windows (3 days before AECOPD, p=0.01, accuracy=0.72 for 5-day windows). CONCLUSIONS: Variability of inspiratory reactance from FOT telemonitoring reflects COPD symptoms and may be a sensitive biomarker to detect AECOPD early.