title: Oxygen delivery-utilization mismatch in contracting locomotor muscle in COPD: peripheral factors.
abstract: Central cardiorespiratory and gas exchange limitations imposed by chronic obstructive pulmonary disease (COPD) impair ambulatory skeletal muscle oxygenation during whole body exercise. This investigation tested the hypothesis that peripheral factors per se contribute to impaired contracting lower limb muscle oxygenation in COPD patients. Submaximal neuromuscular electrical stimulation (NMES; 30, 40, and 50 mA at 50 Hz) of the quadriceps femoris was employed to evaluate contracting skeletal muscle oxygenation while minimizing the influence of COPD-related central cardiorespiratory constraints. Fractional O₂ extraction was estimated by near-infrared spectroscopy (deoxyhemoglobin/myoglobin concentration; deoxy-[Hb/Mb]), and torque output was measured by isokinetic dynamometry in 15 nonhypoxemic patients with moderate-to-severe COPD (SpO2 = 94 ± 2%; FEV₁ = 46.4 ± 10.1%; GOLD II and III) and in 10 age- and gender-matched sedentary controls. COPD patients had lower leg muscle mass than controls (LMM = 8.0 ± 0.7 kg vs. 8.9 ± 1.0 kg, respectively; P < 0.05) and produced relatively lower absolute and LMM-normalized torque across the range of NMES intensities (P < 0.05 for all). Despite producing less torque, COPD patients had similar deoxy-[Hb/Mb] amplitudes at 30 and 40 mA (P > 0.05 for both) and higher deoxy-[Hb/Mb] amplitude at 50 mA (P < 0.05). Further analysis indicated that COPD patients required greater fractional O₂ extraction to produce torque (i.e., ↑Δdeoxy-[Hb/Mb]/torque) relative to controls (P < 0.05 for 40 and 50 mA) and as a function of NMES intensity (P < 0.05 for all). The present data obtained during submaximal NMES of small muscle mass indicate that peripheral abnormalities contribute mechanistically to impaired contracting skeletal muscle oxygenation in nonhypoxemic, moderate-to-severe COPD patients.
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, School of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil;
authors.forename: Wladimir M
authors.initials: WM
authors.lastname: Medeiros
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, School of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil;
authors.forename: Mari C T
authors.initials: MC
authors.lastname: Fernandes
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, School of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil;
authors.forename: Diogo P
authors.initials: DP
authors.lastname: Azevedo
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, School of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil;
authors.forename: Flavia F M
authors.initials: FF
authors.lastname: de Freitas
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, School of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil;
authors.forename: Beatriz C
authors.initials: BC
authors.lastname: Amorim
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, School of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil;
authors.forename: Luciana D
authors.initials: LD
authors.lastname: Chiavegato
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, School of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil; Laboratory of Clinical Exercise Physiology (LACEP), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University, Kingston, Canada; and.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Hirai
authors.affiliation: Respiratory Investigation Unit (RIU), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University, Kingston, Canada.
authors.forename: Denis E
authors.initials: DE
authors.lastname: O'Donnell
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, School of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil; Laboratory of Clinical Exercise Physiology (LACEP), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University, Kingston, Canada; and nederalb@gmail.com.
authors.forename: J Alberto
authors.initials: JA
authors.lastname: Neder
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D029424:Pulmonary Disease, Chronic Obstructive / Q000378:metabolism*; D011659:Pulmonary Gas Exchange / Q000502:physiology
chemical_list: D009211:Myoglobin; D010100:Oxygen
keywords: chronic obstructive pulmonary disease; exercise; near-infrared spectroscopy; neuromuscular electrical stimulation; skeletal muscle; torque