Impact of exercise training and supplemental oxygen on submaximal exercise performance in patients with COPD

Abstract

Functional impairment caused by chronic obstructive pulmonary disease (COPD) impacts on activities of daily living and quality of life. Indeed, patients' submaximal exercise capacity is of crucial importance. It was the aim of this study to investigate the effects of an exercise training intervention with and without supplemental oxygen on submaximal exercise performance. This is a secondary analysis of a randomized, controlled, double-blind, crossover trial. 29 COPD patients (63.5 ± 5.9 years; FEV₁ 46.4 ± 8.6%) completed two consecutive 6-week periods of high-intensity interval cycling and strength training, which was performed three times/week with either supplemental oxygen or medical air (10 L/min). Submaximal exercise capacity as well as the cardiocirculatory, ventilatory, and metabolic response were evaluated at isotime (point of termination in the shortest cardiopulmonary exercise test), at physical work capacity at 110 bpm of heart rate (PWC 110), at the anaerobic threshold (AT), and at the lactate-2 mmol/L threshold. After 12 weeks of exercise training, patients improved in exercise tolerance, shown by decreased cardiocirculatory (heart rate, blood pressure) and metabolic (respiratory exchange ratio, lactate) effort at isotime; ventilatory response was not affected. Submaximal exercise capacity was improved at PWC 110, AT and the lactate-2 mmol/L threshold, respectively. Although supplemental oxygen seems to affect patients' work rate at AT and the lactate-2 mmol/L threshold, no other significant effects were found. The improved submaximal exercise capacity and tolerance might counteract patients' functional impairment. Although cardiovascular and metabolic training adaptations were shown, ventilatory efficiency remained essentially unchanged. The impact of supplemental oxygen seems less important on submaximal training effects.

Keywords: cardiopulmonary exercise test; chronic obstructive pulmonary disease; exercise capacity; interval training; strength training.

Figure 1

The study design. All included patients underwent a training‐free run‐in period lasting 6 weeks to optimize pharmacologic treatment according to international guidelines. Forty‐four patients were randomized at training start to group “O₂ → Air” or group “Air → O₂ ^” and performed two 6‐week periods of exercise training; patients started the training program with supplemental oxygen followed by medical air or vice versa. Participants, caregivers, and those assessing outcomes were blinded for the provided gas supply. Study investigations, analyzing contemporarily all study outcomes, were performed at run‐in start, training start, crossover, and training end. A timeline (weeks) is shown at the bottom of Figure 1

Figure 2

Flow diagram. Fifty of 137 contacted patients met eligibility criteria and entered the run‐in phase. An external block randomization was carried out at training start to ensure a blinded and concealed allocation of a similar number of patients to the two study groups. Although during the training periods 15 patients dropped out, no differences in dropout rates were observed between groups. Furthermore, only two patients opted out during the training period, at a very early stage of the intervention. Other withdrawals were because of comorbidities and exacerbations during the cold winter months

Figure 3

Submaximal thresholds of work rate and VO₂. Work rate (Watt) (A) and oxygen consumption (VO₂) (B) at the Anaerobic Threshold (AT), the lactate threshold at 2 mmol^.L⁻¹ (Lac2) and the Physical Work Capacity at 110 bpm of heart rate (PWC 110) at training start (blue dots) and training end (green dots). Column height representing mean values ± standard error as error bars; individual values are plotted as dots. A number of included patients are depicted at the base of each column. Statistically significant changes are marked with * P < .05, **P < .01, ***P < .001