Daily step count predicts acute exacerbations in a US cohort with COPD

PLoS One. 2013 Apr 4;8(4):e60400. doi: 10.1371/journal.pone.0060400. Print 2013.

Abstract

Background: COPD is characterized by variability in exercise capacity and physical activity (PA), and acute exacerbations (AEs). Little is known about the relationship between daily step count, a direct measure of PA, and the risk of AEs, including hospitalizations.

Methods: In an observational cohort study of 169 persons with COPD, we directly assessed PA with the StepWatch Activity Monitor, an ankle-worn accelerometer that measures daily step count. We also assessed exercise capacity with the 6-minute walk test (6MWT) and patient-reported PA with the St. George's Respiratory Questionnaire Activity Score (SGRQ-AS). AEs and COPD-related hospitalizations were assessed and validated prospectively over a median of 16 months.

Results: Mean daily step count was 5804±3141 steps. Over 209 person-years of observation, there were 263 AEs (incidence rate 1.3±1.6 per person-year) and 116 COPD-related hospitalizations (incidence rate 0.56±1.09 per person-year). Adjusting for FEV1 % predicted and prednisone use for AE in previous year, for each 1000 fewer steps per day walked at baseline, there was an increased rate of AEs (rate ratio 1.07; 95%CI = 1.003-1.15) and COPD-related hospitalizations (rate ratio 1.24; 95%CI = 1.08-1.42). There was a significant linear trend of decreasing daily step count by quartiles and increasing rate ratios for AEs (P = 0.008) and COPD-related hospitalizations (P = 0.003). Each 30-meter decrease in 6MWT distance was associated with an increased rate ratio of 1.07 (95%CI = 1.01-1.14) for AEs and 1.18 (95%CI = 1.07-1.30) for COPD-related hospitalizations. Worsening of SGRQ-AS by 4 points was associated with an increased rate ratio of 1.05 (95%CI = 1.01-1.09) for AEs and 1.10 (95%CI = 1.02-1.17) for COPD-related hospitalizations.

Conclusions: Lower daily step count, lower 6MWT distance, and worse SGRQ-AS predict future AEs and COPD-related hospitalizations, independent of pulmonary function and previous AE history. These results support the importance of assessing PA in patients with COPD, and provide the rationale to promote PA as part of exacerbation-prevention strategies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Cohort Studies
  • Exercise Test*
  • Female
  • Hospitalization / statistics & numerical data
  • Humans
  • Male
  • Middle Aged
  • Prognosis
  • Pulmonary Disease, Chronic Obstructive / diagnosis*
  • Pulmonary Disease, Chronic Obstructive / drug therapy
  • Pulmonary Disease, Chronic Obstructive / epidemiology
  • United States
  • Walking*

Grant support

The research reported here was supported by the Department of Veteran Affairs, Veterans Health Administration, Rehabilitation Research and Development Service through a VA Career Development Award to Dr. Moy. Supported in part by CIMIT: Center for Integration of Medicine and Innovative Technology (Dr. Moy). Supported in part by VA Rehabilitation Research and Development Merit Review Grant B6618R (Dr. Garshick). This study was initiated by the investigators. The results of the present study do not constitute endorsement of the StepWatch Activity Monitor by the authors. Orthocare Innovations had no involvement in the study design, the collection, analysis, and interpretation of data, in the writing of the manuscript, or in the decision to submit the paper for publication. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.