Functional and psychological variables both affect daily physical activity in COPD: a structural equations model.

BACKGROUND Daily physical activity (DPA) level is reduced in patients with COPD. The aim of this study was to investigate the association of DPA with functional and psychological variables in these patients. METHODS 155 COPD patients (102 males, median (IQR) age 62 years (54-69 years), predicted FEV1 60% (40-75%) were included. We assessed DPA (DigiWalker SW-200), functional capacity and psychological factors. RESULTS DPA level was significantly associated with all functional capacity variables and two psychological variables (Perceived Physical Ability Subscale, depression subscale of the Hospital Anxiety and Depression Scale). The six-minute walking distance and St. George Respiratory Questionnaire activity score explained 37% of the variance of DPA in a regression analysis. A structural equations model revealed that psychological variables indirectly explained DPA through functional capacity variables. DPA was stronger associated with functional capacity variables and weaker with psychological variables in patients with lower functional status than in patients with higher functional status. CONCLUSIONS Higher levels of DPA are associated with better functional capacity, but interestingly, DPA is also affected by psychological factors, though only indirectly, via functional capacity. The effect of specific treatment addressing psychological factors on DPA level and exercise tolerance needs further investigation. CLINICAL TRIAL REGISTRATION ClinicalTrials.gov, NCT00614796.