title: Quantitating physical activity in COPD using a triaxial accelerometer.
abstract: OBJECTIVE
  To determine the reliability, validity, and stability of a triaxial accelerometer for walking and daily activity measurement in a COPD sample.
  
  
  METHODS
  Cross-sectional, correlational, descriptive design.
  
  
  METHODS
  Outpatient pulmonary rehabilitation program in a university-affiliated Veterans Affairs medical center.
  
  
  METHODS
  Forty-seven outpatients (44 men and 3 women) with stable COPD (FEV(1), 37% predicted; SD, 16%) prior to entry into a pulmonary rehabilitation program.
  
  
  RESULTS
  Test-retest reliability of a triaxial movement sensor (Tritrac R3D Research Ergometer; Professional Products; Madison, WI) was evaluated in 35 of the 47 subjects during three standardized 6-min walks (intraclass correlation coefficient [rICC] = 0.84). Pearson correlations evaluated accelerometer concurrent validity as a measure of walking (in vector magnitude units), compared to walking distance in all 47 subjects during three sequential 6-min walks (0. 84, 0.85, and 0.95, respectively; p < 0.001). The validity of the accelerometer as a measure of daily activity over 3 full days at home was evaluated in all subjects using Pearson correlations with other indicators of functional capacity. The accelerometer correlated with exercise capacity (maximal 6-min walk, r = 0.74; p < 0.001); level of obstructive disease (FEV(1) percent predicted, r = 0.62; p < 0.001); dyspnea (Functional Status and Dyspnea Questionnaire, dyspnea over the past 30 days, r = - 0.29; p < 0.05); and activity self-efficacy (Activity Self-Efficacy Questionnaire, r = 0.43; p < 0.01); but not with self-report of daily activity (Modified Activity Recall Questionnaire, r = 0.14; not significant). Stability of the accelerometer to measure 3 full days of activity at home was determined by an rICC of 0.69.
  
  
  CONCLUSIONS
  This study provides preliminary data suggesting that a triaxial movement sensor is a reliable, valid, and stable measure of walking and daily physical activity in COPD patients. It has the potential to provide more precise measurement of everyday physical functioning in this population than self-report measures currently in use, and measures an important dimension of functional status not previously well-described.
authors.affiliation: Department of Biobehavioral Nursing and Health, University of Washington School of Nursing, Seattle, WA 98108, USA. Bonnie.Steele@med.va.gov
authors.forename: B G
authors.initials: BG
authors.lastname: Steele
authors.forename: L
authors.initials: L
authors.lastname: Holt
authors.forename: B
authors.initials: B
authors.lastname: Belza
authors.forename: S
authors.initials: S
authors.lastname: Ferris
authors.forename: S
authors.initials: S
authors.lastname: Lakshminaryan
authors.forename: D M
authors.initials: DM
authors.lastname: Buchner
mesh_terms: D000203:Activities of Daily Living / Q000145:classification*; D000368:Aged; D000369:Aged, 80 and over; D000553:Ambulatory Care; D003430:Cross-Sectional Studies; D004867:Equipment Design; D005080:Exercise Test / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000175:diagnosis / Q000534:rehabilitation*; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D015203:Reproducibility of Results; D016138:Walking / Q000145:classification*