Disease-specific muscle oxygen transport and utilization during exercise in chronic obstructive pulmonary disease vs. chronic heart failure

Abstract

Aim: We investigated muscle convective and diffusive oxygen (O₂) transport in chronic obstructive pulmonary disease (COPD) compared with healthy controls (CON) and heart failure (HF) patients during one-legged knee-extensor exercise to determine disease-specific differences in peripheral determinants during exercise with a small muscle mass.

Methods: Eight patients with moderate to severe COPD, eight patients with HF and eight age- and sex-matched controls were studied. We measured leg blood flow (LBF) by Doppler ultrasound during submaximal one-legged knee-extensor exercise, while sampling arteriovenous variables across the leg in all subjects during rest and exercise. The capillary oxyhemoglobin dissociation curve was reconstructed from paired femoral arterial-venous oxygen tensions and saturations, which enabled the estimation of O₂ parameters in the capillaries of the contracting muscle.

Results: Exercising LBF increased to a similar extent in HF (2.0(0.4) L/min) and CON (2.3(0.3) L/min), but was lower in COPD patients (1.8(0.3) L/min)(p<0.05). Muscle O₂ extraction increased in COPD and CON during exercise (p<0,05), but not in HF. Muscle O₂ consumption increased during exercise in all three groups, with no differences between groups, and the blood flow conductance (DO₂) increased simirlarly, but when adjusting for flow, the DO₂ was unchanged in the HF group.

Conclusion: Disease-specific factors may play a role in peripheral exercise capacity in patients with COPD vs. HF. Thus, low convective O₂ transport to contracting muscle seemed to predominate the exercise limitation in COPD, whereas muscle O₂ diffusive capacity was blunted in HF.