Directly measured physical activity as a predictor of hospitalizations in patients with chronic obstructive pulmonary disease

Abstract

Patients with clinically stable chronic obstructive pulmonary disease (COPD) are physically inactive, and this inactivity appears to be an independent predictor of hospitalizations. To explore this relationship further, we compared physical activity of COPD patients assessed in 2008 to subsequent hospitalizations and mortality. Sixty adults with a history of cigarette smoking, a diagnosis of COPD, a forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) of <0.70, and no recent exacerbation were studied. Physical activity was measured using a triaxial accelerometerworn on the waist for seven consecutive days and the vector magnitude units (VMUs) that are the sum of movements in three planes over each minute were recorded. Those patients with mean VMU<170 (the median) were considered to be less physically active, and those with a 6-minute walk distance (6MWD) test of <350 m were considered to have lower functional exercise capacity. These two variables, along with age, gender, and a history of exacerbations in the preceding 12 months, FEV1, body mass index, and supplemental oxygen requirement, were related to subsequent all-cause and respiratory-related hospitalizations that occurred over the ensuing 53±2 months. The mean age was 68±11 years, 50% were male, and the FEV1 was 53±19%. All-cause and respiratory-related hospitalizations occurred in 58 and 35%, respectively. A 6MWD<350 m and VMU<170 each significantly predicted subsequent all-cause and respiratory-related hospitalizations in univariate Cox proportional hazards analyses after controlling for previous exacerbations. Both 6MWD<350 m and VMU<170 counts remained in a multivariate model predicting respiratory-related hospitalization. These results indicate that both directly measured physical activity and functional exercise capacity are important predictors of hospitalization in COPD.

Keywords: COPD exacerbation; Chronic obstructive pulmonary disease; accelerometer; health care utilization; vector magnitude units.