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Background: Many telehealth (TH) systems have been designed to identify signs of COPD exacerbations, but few previous studies have reported the nature of recorded lung function data and what variations to expect in stable versus unstable patients.

Aims: To evaluate the nature of individual diurnal, day-to-day and long-term variation in important prognostic markers of COPD exacerbations in a heterogeneous patient group by employing a newly developed TH system.

Methods: Eight women and five men with COPD performed measurements (FEV1, IC, SpO2 and CAT) three times per week during 4-6 months using the TH system. Feasibility was based on the repeatability and quality of the FEV1 and IC measurements, as defined by ERS/ATS guidelines. Short-term and long-term individual variations were assessed using the relative density and mean (SD) respectively.

Results: Close to 1100 FEV1 and IC measurements respectively were performed during a total of 240 patient weeks. The 2SD ranges for intra-individual variation were ± 210 mL and ± 350 mL for FEV1 and IC respectively. The values both increased and decreased without corresponding influence on symptoms (CAT) or SpO2 and no exacerbation was reported. However, it was unusual with a decrease of more than 50 mL per measurement in FEV1 between three consecutive measurement days.

Conclusions: This study reveals important and, to our knowledge, previously not reported information about short and long-term variability in lung function measurements in stable patients with COPD, of significance when defining criteria for detecting exacerbations with TH systems.