Background: Accelerometry is increasingly used to assess physical activity (PA) in patients with chronic obstructive pulmonary disease (COPD). It is not known how the relationship of PA to clinical results depends on the position of the PA sensor.
Methods: We assessed the effect of monitor position by measuring lower extremity (ankle), upper extremity (wrist) and total body movement (hip) in 52 patients with severe COPD (mean [± SD] age, 62 ± 10 years; FEV(1), 38 ± 12% predicted) undergoing long-term oxygen therapy with and without walkers during a pulmonary rehabilitation (PR) program. Sensors were worn 8.5 ± 3.1 days and data was compared to the BODE score and the 6-minute walk distance (6MWD) assessed at the beginning and end of the PR.
Results: Mean ankle PA was moderately related to the 6MWD, irrespective of patients being equipped with a walker or not (p < 0.05). Mean PA values were considerably lower in COPD patients with walker compared to patients without for all sensor positions. No significant association was observed between mean hip PA data and 6MWD; however, hip and ankle PA data were moderately related in walker-free and strongly related in walker patients (p < 0.01). In a multivariate regression model only ankle activity was significantly associated with the BODE score (p < 0.01).
Conclusion: The sensor position had a significant impact on the association between PA recordings and the 6MWD in very severe COPD. In our setting, ankle measurement seemed to best reflect the clinical state of patients.