High oxygen extraction and slow recovery of muscle deoxygenation kinetics after neuromuscular electrical stimulation in COPD patients

Purpose It was hypothesized that patients with chronic obstructive pulmonary disease (COPD) would exhibit a slow muscle deoxygenation (HHb) recovery time when compared with sedentary controls. Methods Neuromuscular electrical stimulation (NMES 40 and 50 mA, 50 Hz, 400 µs) was employed to induce isometric contraction of the quadriceps. Microvascular oxygen extraction (µO 2 EF) and HHb were estimated by near-infrared spectroscopy (NIRS). Recovery kinetic was characterized by measuring the time constant Tau (HHb-τ). Torque and work were measured by isokinetic dynamometry in 13 non-hypoxaemic patients with moderate-to-severe COPD [SpO 2 = 94.1 ± 1.6 %; FEV 1 (% predict) 48.0 ± 9.6; GOLD II–III] and 13 age- and sex-matched sedentary controls. Results There was no desaturation in either group during NMES. Torque and work were reduced in COPD versus control for 40 and 50 mA [torque (Nm) 50 mA = 28.9 ± 6.9 vs 46.1 ± 14.2; work (J) 50 mA = 437.2 ± 130.0 vs. 608.3 ± 136.8; P