title: Six-minute-walk distance and accelerometry predict outcomes in chronic obstructive pulmonary disease independent of Global Initiative for Chronic Obstructive Lung Disease 2011 Group.
abstract: BACKGROUND
  The 2011 combined Global Initiative for Chronic Obstructive Lung Disease (GOLD) assessment incorporates symptoms, exacerbation history, and spirometry in discriminating risk of exacerbations in patients with chronic obstructive pulmonary disease (COPD). Six-minute-walk distance (6MWD) and accelerometry also have been used to assess disease severity in COPD. The association between these measures and the risks of hospitalization and mortality in the context of GOLD 2011 is unknown.
  
  
  OBJECTIVE
  To describe changes in exercise tolerance and physical activity over time in patients with COPD and to test the hypothesis that lower baseline 6MWD or accelerometry step count is associated with increased risk of COPD-related hospitalization or all-cause mortality, independent of GOLD 2011 group.
  
  
  METHODS
  Physical function and medical outcomes were prospectively assessed in 326 patients with moderate to severe COPD in INSPIRE-II, a randomized controlled trial of a coping skills training intervention. Cox models were used to determine if GOLD 2011 group, 6MWD, or accelerometry steps were associated with risk of COPD-related hospitalization or all-cause mortality.
  
  
  RESULTS
  Physical function declined over time in GOLD group D but remained stable in groups A, B, and C. GOLD classification was associated with time to death or first COPD-related hospitalization. Baseline 6MWD was more strongly associated with time to death or first COPD-related hospitalization (hazard ratio, 0.50 [95% confidence interval, 0.34, 0.73] per 150 m, P=0.0003) than GOLD 2011 classification. A similar relationship was observed for accelerometry steps (hazard ratio, 0.80 [95% confidence interval, 0.70, 0.92] per 1,000 steps, P=0.002).
  
  
  CONCLUSIONS
  Exercise tolerance and daily physical activity are important predictors of hospitalization and mortality in COPD, independent of GOLD 2011 classification. Physical function may represent a modifiable risk factor that warrants increased attention as a target for interventions to improve clinically meaningful outcomes in COPD.
authors.affiliation: 1 Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Durheim
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Smith
authors.forename: Michael A
authors.initials: MA
authors.lastname: Babyak
authors.forename: Stephanie K
authors.initials: SK
authors.lastname: Mabe
authors.forename: Tereza
authors.initials: T
authors.lastname: Martinu
authors.forename: Karen E
authors.initials: KE
authors.lastname: Welty-Wolf
authors.forename: Charles F
authors.initials: CF
authors.lastname: Emery
authors.forename: Scott M
authors.initials: SM
authors.lastname: Palmer
authors.forename: James A
authors.initials: JA
authors.lastname: Blumenthal
mesh_terms: D061725:Accelerometry / Q000379:methods*; D000368:Aged; D018450:Disease Progression; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis* / Q000503:physiopathology; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013147:Spirometry; D013997:Time Factors; D016138:Walking / Q000502:physiology*
keywords: accelerometry; chronic obstructive pulmonary disease; exercise; hospitalization; mortality