Pulmonary rehabilitation for COPD improves exercise time rather than exercise tolerance: effects and mechanisms

Abstract

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 (VO 2 ) increased after PR: two factors increased (both the T ex and the peak VO 2 increased); two factors decreased; time only increased (the T ex increased, but the peak VO 2 economized); and VO 2 only increased (the T ex decreased, but the peak VO 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 VO 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 E ) ( P =0.004), VO 2 ( P <0.0001), and carbon dioxide output (VCO 2 ) ( P <0.0001) were lower, 2) V E /VO 2 ( P =0.034) and V E /VCO 2 ( 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. Keywords: cardiopulmonary exercise testing, oxygen requirement, ventilatory equivalents, body weight, carbon dioxide output