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 [Formula: see text] increased after PR: two factors increased (both the T_ex and the peak [Formula: see text] increased); two factors decreased; time only increased (the T_ex increased, but the peak [Formula: see text] economized); and [Formula: see text] only increased (the T_ex decreased, but the peak [Formula: see text] 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 [Formula: see text]), 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 [Formula: see text] (P=0.004), [Formula: see text] (P<0.0001), and carbon dioxide output [Formula: see text] (P<0.0001) were lower, 2) [Formula: see text]/ [Formula: see text] (P=0.034) and [Formula: see text]/ [Formula: see text] (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: body weight; carbon dioxide output; cardiopulmonary exercise testing; oxygen requirement; ventilatory equivalents.

Figure 1

Exercise time (T_ex)/Δ oxygen uptake $\left({\dot{\mathrm{V}}\mathrm{O}}_2\right)$, that is, time–slope. Note: The T_ex standardized by the increase of ${\dot{\mathrm{V}}\mathrm{O}}_2$ from resting to peak exercise during cardiopulmonary exercise testing.

Figure 2

The effects of PR on peak ${\dot{\mathrm{V}}\mathrm{O}}_2$ and T_ex. Note: All patients are classified into four groups by whether the exercise time (T_ex) or the peak oxygen uptake $\left({\dot{\mathrm{V}}\mathrm{O}}_2\right)$ did or did not increase after PR. Abbreviation: PR, pulmonary rehabilitation.

Figure 3

Study flow diagram. Abbreviations: CPET, cardiopulmonary exercise testing; PR, pulmonary rehabilitation.

Figure 4

The changes of exercise variables before and after pulmonary rehabilitation. Notes: In the time only increased group, the data for peak exercise in 18 patients and the data for AT, which were obtained at both pre- and post-PR, in 12 patients were used. In the two factors increased group, the data for peak exercise in 11 patients and the data for AT, which were obtained at both pre- and post-PR, in 10 patients were used. The post-PR results are compared with the pre-PR results within each group (^*P<0.05, ^**P<0.01, ^***P<0.001, ^****P<0.001) and between the two groups (^#P<0.05, ^##P<0.01, ^###P<0.001, ^####P<0.001) using paired t-tests and unpaired t-tests, respectively. Abbreviations: AT, anaerobic threshold; ΔFO₂, the inspired oxygen concentration (FiO₂) minus expired oxygen concentration (FeO₂); peak ex., peak exercise; ${\dot{\mathrm{V}}\text{CO}}_2$, carbon dioxide output; ${\dot{\mathrm{V}}}_{\mathrm{E}}$, minute ventilation; ${\dot{\mathrm{V}}\mathrm{O}}_2$, oxygen uptake.

Figure 5

Correlation between the ratio of the post-to-pre-change ratio of the time–slope and the baseline time–slope. Abbreviation: PR, pulmonary rehabilitation.