Evaluation of a new motion sensor in patients with chronic obstructive pulmonary disease

Objective: To assess the criterion validity and reproducibility of a new pedometer in patients with chronic obstructive pulmonary disease (COPD).

Design: Cross-sectional study.

Setting: Outpatient physiotherapy clinic from a university hospital.

Participants: Patients with COPD (N=30; 17 men; forced expiratory volume in the first second, 44±17% predicted) were videotaped while performing 2 protocols: one including 2 slow and 2 fast 5-minute walks, and another including a circuit of activities of daily living (ADLs). Concomitantly, patients wore 2 motion sensors: the new pedometer and a multisensor accelerometer.

Interventions: None.

Main outcome measures: Step counting (SC), energy expenditure (EE), walking distance (WD), activity time (AT), and walking intensity (WI) registered by the pedometer were compared with video and the multisensor as criterion methods.

Results: Correlations between the pedometer and the criterion method were high for SC during slow and fast walking (r=.79 and r=.95) and for EE during fast walking (r=.83). Correlation was more modest for EE during slow walking (r=.65) and for WD and WI during both speeds (.47<r<.68). The agreement between methods was also good, according to Bland-Altman plots. The device was reproducible for registering SC, WD, and EE during slow walking and for all variables during fast walking (intraclass correlation coefficient >.79 for all). During the ADLs circuit, the pedometer underestimated AT by an average of 55% but provided an acceptable EE estimation in a group basis (average difference of 6% with the multisensor).

Conclusions: In patients with COPD, the new pedometer analyzed in the present study is reproducible for most outcomes and highly valid for SC during slow and fast walking and EE during fast walking. The device's validity is more limited for EE during slow walking, and WD and WI at both speeds. Furthermore, during the performance of ADLs, it significantly underestimates activity time but provides an acceptable estimation of EE in a group basis.