title: Oxygen delivery and the restoration of the muscle energetic balance following exercise: implications for delayed muscle recovery in patients with COPD.
abstract: Patients with chronic obstructive pulmonary disease (COPD) experience a delayed recovery from skeletal muscle fatigue following exhaustive exercise that likely contributes to their progressive loss of mobility. As this phenomenon is not well understood, this study sought to examine postexercise peripheral oxygen (O2) transport and muscle metabolism dynamics in patients with COPD, two important determinants of muscle recovery. Twenty-four subjects, 12 nonhypoxemic patients with COPD and 12 healthy subjects with a sedentary lifestyle, performed dynamic plantar flexion exercise at 40% of the maximal work rate (WRmax) with phosphorus magnetic resonance spectroscopy (31P-MRS), near-infrared spectroscopy (NIRS), and vascular Doppler ultrasound assessments. The mean response time of limb blood flow at the offset of exercise was significantly prolonged in patients with COPD (controls: 56 ± 27 s; COPD: 120 ± 87 s;P< 0.05). In contrast, the postexercise time constant for capillary blood flow was not significantly different between groups (controls: 49 ± 23 s; COPD: 51 ± 21 s;P> 0.05). The initial postexercise convective O2delivery (controls: 0.15 ± 0.06 l/min; COPD: 0.15 ± 0.06 l/min) and the corresponding oxidative adenosine triphosphate (ATP) demand (controls: 14 ± 6 mM/min; COPD: 14 ± 6 mM/min) in the calf were not significantly different between controls and patients with COPD (P> 0.05). The phosphocreatine resynthesis time constant (controls: 46 ± 20 s; COPD: 49 ± 21 s), peak mitochondrial phosphorylation rate, and initial proton efflux were also not significantly different between groups (P> 0.05). Therefore, despite perturbed peripheral hemodynamics, intracellular O2availability, proton efflux, and aerobic metabolism recovery in the skeletal muscle of nonhypoxemic patients with COPD are preserved following plantar flexion exercise and thus are unlikely to contribute to the delayed recovery from exercise in this population.
authors.affiliation: Department of Medicine, Division of Geriatrics, University of Utah, Salt Lake City, Utah; gwenael.layec@utah.edu.|Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah.|Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, Utah.
authors.forename: Gwenael
authors.initials: G
authors.lastname: Layec
authors.affiliation: Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, Utah.
authors.forename: Corey R
authors.initials: CR
authors.lastname: Hart
authors.affiliation: Department of Medicine, Division of Geriatrics, University of Utah, Salt Lake City, Utah.|Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah.|Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, Utah.
authors.forename: Joel D
authors.initials: JD
authors.lastname: Trinity
authors.affiliation: Department of Medicine, Division of Geriatrics, University of Utah, Salt Lake City, Utah.|Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah.
authors.forename: Oh-Sung
authors.initials: OS
authors.lastname: Kwon
authors.affiliation: Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, Utah.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Rossman
authors.affiliation: Department of Medicine, Division of Geriatrics, University of Utah, Salt Lake City, Utah.|Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Broxterman
authors.affiliation: Centre de Résonance Magnétique Biologique et Médicale, Aix-Marseille Universite, Centre National de la Recherche Scientifique, Marseille, France; and.
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Fur
authors.affiliation: Department of Radiology and Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah.
authors.forename: Eun-Kee
authors.initials: EK
authors.lastname: Jeong
authors.affiliation: Department of Medicine, Division of Geriatrics, University of Utah, Salt Lake City, Utah.|Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah.|Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, Utah.
authors.forename: Russell S
authors.initials: RS
authors.lastname: Richardson
mesh_terms: D000368:Aged; D004734:Energy Metabolism; D015444:Exercise; D005081:Exercise Therapy / Q000379:methods; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D008297:Male; D018763:Muscle Fatigue; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010101:Oxygen Consumption; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D020127:Recovery of Function / Q000502:physiology*
keywords: 31P-MRS; COPD; O2 availability; PCr recovery kinetics; mitochondrial function; muscle fatigue