Exercise training in COPD: muscle O2 transport plasticity

Abstract

Both convective oxygen (O2) transport to, and diffusive transport within, skeletal muscle are markedly diminished in patients with COPD. However, it is unknown how these determinants of peak muscle O2 uptake (V′mO2peak) respond to exercise training in patients with COPD. Therefore, the purpose of this study was to assess the plasticity of skeletal muscle O2 transport determinants of V′mO2peak in patients with COPD.Adaptations to 8 weeks of single-leg knee-extensor exercise training were measured in eight patients with severe COPD (mean±sem forced expiratory volume in 1 s (FEV1) 0.9±0.1 L) and eight healthy, well-matched controls. Femoral arterial and venous blood samples, and thermodilution-assessed leg blood flow were used to determine muscle O2 transport and utilisation at maximal exercise pre- and post-training.Training increased V′mO2peak in both COPD (by ∼26% from 271±29 to 342±35 mL·min−1) and controls (by ∼32% from 418±37 to 553±41 mL·min−1), restoring V′mO2peak in COPD to only ∼80% of pre-training control V′mO2peak. Muscle diffusive O2 transport increased similarly in both COPD (by ∼38% from 6.6±0.9 to 9.1±0.9 mL·min−1·mmHg−1) and controls (by ∼36% from 10.4±0.7 to 14.1±0.8 mL·min−1·mmHg−1), with the patients reaching ∼90% of pre-training control values. In contrast, muscle convective O2 transport increased significantly only in controls (by ∼26% from 688±57 to 865±69 mL·min−1), leaving patients with COPD (438±45 versus 491±51 mL·min−1) at ∼70% of pre-training control values.While muscle diffusive O2 transport in COPD was largely restored by exercise training, V′mO2peak remained constrained by limited plasticity in muscle convective O2 transport.