Pulmonary Rehabilitation for COPD Improves Exercise Time Rather Than Exercise Tolerance: Effects and Mechanisms

Background: COPD patients undergoing pulmonary rehabilitation (PR) show various responses. The purpose of this study was to investigate the possible mechanisms and predictors of the response to PR in COPD patients.Methods: Thirty-six stable COPD patients underwent PR including a 4-week high-intensity exercise training program, and they were evaluated by cardiopulmonary exercise testing. All patients (mean age 69 years, severe and very severe COPD 94%) were classified into four groups by whether the exercise time (T-ex) or the peak oxygen uptake ((V) over dotO(2)) increased after PR: two factors increased (both the T-ex and the peak (V) over dotO(2) increased); two factors decreased; time only increased (the T-ex increased, but the peak (V) over dotO(2) economized); and (V) over dotO(2) only increased (the T-ex decreased, but the peak (V) over dotO(2) increased). Within all patients, the relationships between baseline variables and the post-to-pre-change ratio of the time-slope, T-ex/(peak minus resting (V) over dotO(2)), were investigated.Results: Compared with the two factors increased group (n=11), in the time only increased group (n=18), the mean differences from pre-PR at peak exercise in 1) minute ventilation ((V) over dot E) (P=0.004), (V) over dotO(2) (P<0.0001), and carbon dioxide output ((V) over dot CO2) (P<0.0001) were lower, 2) (V) over dot(E)/(V) over dotO(2) (P=0.034) and (V) over dot E/(V) over dot CO2 (P=0.006) were higher, and 3) the dead space/tidal volume ratio (V-D/V-T) and the dyspnea level were similar. After PR, there was no significant difference in the ratio of the observed peak heart rate (HR) to the predicted peak HR (220 - age [years]) between the two groups. A significant negative correlation with the baseline time-slope (r=-0.496, P=0.002) and a positive correlation with the baseline body mass index (BMI) (r=0.496, P=0.002) were obtained.Conclusions: PR in COPD patients improves T-ex rather than exercise tolerance, economizing oxygen requirements, resulting in reduced ventilatory requirements without cardiac loads followed by reduced exertional dyspnea. In addition, the time-slope and BMI could be used to predict PR responses beforehand.