Lower limb vasodilatory capacity is not reduced in patients with moderate COPD

Surendran Sabapathy¹, Marc F Awater², Donald A Schneider¹, Rebecca A Kingsley¹, Maria TE Hopman², Norman R Morris¹

¹School of Physiotherapy and Exercise Science, and Heart Foundation Research Centre, Gold Coast campus, Griffith University, QLD, Australia; ²Department of Physiology, University of Nijmegen, Nijmegen, The Netherlands

Abstract: We compared exercise capacity (peak O₂ uptake; VO_2peak) and lower limb vasodilatory capacity in 9 patients with moderate COPD (FEV₁ 52.7 ± 7.6% predicted) and 9 age-matched healthy control subjects.  VO_2peak was measured via open circuit spirometry during incremental cycling. Calf blood flow (CBF) measurements were obtained at rest and after 5 minutes of ischemia using venous occlusion plethysmography. While VO_2peak was significantly lower in the COPD patients (15.8 ± 3.5 mL·kg^–1·min^–1) compared with the control group (25.2 ± 3.5 mL·kg^–1·min^–1), there were no significant differences between groups in peak CBF or peak calf conductance measured 7 seconds post-ischemia. VO_2peak was significantly correlated with peak CBF and peak conductance in the control group, whereas no significant relationship was found between these variables in the COPD group. However, the rate of decay in blood flow following ischemia was significantly slower (p < 0.05) for the COPD group (–0.036 ± 0.005 mL·100 mL^–1·min^–1·s^–1) when compared with controls (–0.048 ± 0.015 mL·100mL^–1·min^–1·s^–1). The results suggest that the lower peak exercise capacity in patients with moderate COPD is not related to a loss in leg vasodilatory capacity.

Keywords: obstructive lung disease, exercise capacity, reactive hyperemia, calf blood flow