Validation of the triaxial accelerometer for the evaluation of physical activity in Japanese patients with COPD

The quantification of physical activity is useful for the management of chronic obstructive pulmonary disease (COPD) but has not been fully established yet. The DynaPort Activity Monitor(®) (DAM), a triaxial accelerometer is the only well validated accelerometer in Caucasians but it has not been validated in Japanese COPD patients. We initially evaluated the reproducibility of the DAM in Japanese healthy subjects. Next, the within-subject repeatability and the determinants of physical activity were investigated in Japanese COPD patients.

The durations of locomotion, standing, and sitting measured by the DAM were compared to those of the self-records (Study 1). COPD patients wore the DAM for 3 days and the durations of each activity of 2 selected days were compared to assess the repeatability (Study 2). The relationship between the duration of locomotion and the physiological properties were examined (Study 3).

The activities measured by the DAM were significantly associated with those of the self-records (p<0.001). The values of the intra-class correlation coefficient (ICC) for the reproducibility were over 0.99, and the agreement with the self-records was observed for the DAM. Similarly, the values of ICC for repeatability were over 0.84 in all activities, and there was no systematic bias in the COPD patients. The duration of locomotion was negatively correlated with the total lung capacity (TLC) and closing capacity/TLC, but not with other pulmonary functions, exercise capacity, muscle force, dyspnea, or modified BODE index.

The triaxial accelerometer is reliable for evaluating the physical activity of Japanese COPD patients.