Cycling Efficiency Is Not Compromised for Moderate Exercise in Moderately Severe COPD

Abstract

Hyperpnea and hyperinflation have been proposed as contributors to exaggerated energy demands in chronic obstructive pulmonary disease (COPD), yet there are incomplete data on exercise requirements. This study compared total-body energy demands of the internal (unloaded) and external work of cycling and delta mechanical efficiency in 40 patients (FEV1: 36+/-14% predicted) with COPD and 28 healthy age-matched controls while characterizing dynamic hyperinflation. Steady-state V O2 was obtained at rest, during unloaded and 20-W cycling, and at 20, 50, and 65% peak cycling power. Delta mechanical efficiency was calculated between constant-load cycling at 65 and 20% peak power. Dynamic hyperinflation was assessed from inspiratory capacity maneuvers. Oxygen demands (L.min) at rest, for internal work (0.47+/-0.14 vs 0.45+/-0.11) or external work at 20 W (0.62+/-0.20 vs 0.57+/-0.13), were not different between patients and controls, although ventilation was elevated in COPD. Cycling at 65% of peak power induced dynamic hyperinflation in COPD, which indices were not related to cycling efficiency. Delta efficiency (%) was not different between patients (26.3+/-8.1) and controls (24.8+/-4.0). Findings suggest that bioenergetics of submaximal cycling is not compromised in moderately severe COPD despite tachypnea and dynamic hyperinflation.