Determinants of annual change in physical activity in COPD

Background and objective: Daily physical activity (PA) is reduced in patients with COPD. Previous cross-sectional analyses indicate various predictors for a low level of PA including airway obstruction, exacerbations and co-morbidities. However, information from longitudinal studies evaluating PA in the context of disease progression, survival and co-morbidities is scant.

Methods: In a heterogeneous cohort of COPD patients, we annually assessed the number of steps per day over 1 week and potential determinants including lung function, exacerbations and co-morbidities. Univariable and multivariable mixed effect models were used to investigate associations between the change in steps per day (dependent variable) and possible predictors and their annual changes.

Results: A total of 177 COPD patients (46% GOLD (Global Initiative for Chronic Obstructive Lung Disease) stage 1/2, 38% stage 3 and 16% stage 4) with a mean (min/max) follow-up time of 2.7 (1/5) years were annually assessed. The number of steps per day decreased significantly over time (P < 0.001) with a mean annual change of -508 steps. The decrease in activity was significantly associated with forced expiratory volume in 1 s (FEV₁ ) % predicted (P = 0.020) but not with annual changes in FEV₁ . Hyperinflation, exacerbations, co-morbidities and their annual changes, and survival did not significantly affect change in PA.

Conclusion: COPD patients have a substantial decrease of PA over time. This decrease seems to be determined by the degree of airflow limitation. However, patients with a greater annual decline in lung function did not show a greater decrease in PA. The rate of decline in PA did not differ between survivors and non-survivors in this cohort.