Survival after pulmonary rehabilitation in patients with COPD: impact of functional exercise capacity and its changes

Abstract

The impact of rehabilitation-induced changes in 6-minute walk distance (6MWD) on the survival of patients with chronic obstructive pulmonary disease (COPD) has not been fully elucidated. This study sought to determine the association of baseline 6MWD and its changes after pulmonary rehabilitation (PR) with 5-year survival in patients with COPD. Patients who were referred to a 12-week outpatient PR program were followed up for 5 years post-completion, and survival status was verified. Survival was analyzed according to four groups based upon initial 6MWD (6MWDi) and its changes (Delta 6MWD) after PR (Group 1: 6MWDi >= 350 m and Delta 6MWD >= 30 m; Group 2: 6MWDi >= 350 m and Delta 6MWD <30 m; Group 3: 6MWDi <350 m and D6MWD >= 30 m; and Group 4: 6MWDi <350 m and D6MWD <30 m) via Kaplan-Meier analysis and log rank test. Cox regression was performed to identify possible confounders of mortality estimates. In total, 423 patients (with mean +/- standard deviation of forced expiratory volume in the first second [FEV1] 43 +/- 16% predicted, age 65 +/- 8 years, and 6WMDi 381 +/- 134 m) underwent PR between 1999 and 2010. Survival rates decreased progressively from Group 1 to Group 4 (Group 1, 81%; Group 2, 69%; Group 3, 47%; Group 4, 27%; log rank test, P<0.05). 6MWDi >350 m (hazard ratio [HR] 0.39 [95% confidence interval {CI} 0.30-0.50]) and D6MWD >= 30 m (HR 0.66 [95% CI 0.51-0.85]) were strongly and independently associated with survival. Compared with Group 1, mortality risks progressively increased in Group 2 (HR 1.36 [95% CI 0.92-2.00]; not significant), Group 3 (HR 1.90 [95% CI 1.28-2.84]; P=0.001), and Group 4 (HR 3.28 [95% CI 2.02-5.33]; P=0.0001). Both poor 6MWD and lack of improvement >30 m after PR are associated with worse 5-year survival in patients with COPD.