title: Metabolic myopathies: functional evaluation by analysis of oxygen uptake kinetics.
abstract: OBJECTIVE
  The aim was to identify additional noninvasive tools allowing to detect and to quantify the metabolic impairment in patients with mitochondrial myopathies (MM) or McArdle's disease (McA).
  
  
  METHODS
  Kinetics of adjustment of pulmonary oxygen uptake (VO2 kinetics) during transitions to constant-load moderate-intensity cycle ergometer exercise were determined on 15 MM, 8 McA, 21 patients with signs and/or symptoms of metabolic myopathy but a negative biopsy ("patient controls"; P-CTRL), and 22 healthy untrained controls (CTRL).
  
  
  RESULTS
  VO2 kinetics were slower in MM and in McA versus P-CTRL and CTRL, slower in McA versus MM, and not significantly different between P-CTRL and CTRL. The time constants (tau) of the monoexponential function describing the VO2 kinetics were (X +/- SE) 59.2 +/- 8.5 s in MM, 87.6 +/- 16.4 s in McA, 36.9 +/- 3.1 s in P-CTRL, and 35.4 +/- 1.9 s in CTRL. In a subgroup of the patients (eight MM and seven McA), tau of VO2 kinetics were negatively correlated with two variables determined in a previous study (Grassi B, Marzorati M, Lanfranconi F, et al. Impaired oxygen extraction in metabolic myopathies: detection and quantification by near-infrared spectroscopy. Muscle Nerve. 2007;35:510-20): a) a muscle oxygenation index, obtained by near-infrared spectroscopy, estimating the peak capacity of skeletal muscle fractional O2 extraction; and b) VO2 peak.
  
  
  CONCLUSIONS
  In MM and McA patients, analysis of pulmonary VO2 kinetics during moderate-intensity exercise allows to identify and to quantify, noninvasively, the impairment of skeletal muscle oxidative metabolism. In these patients, the slower VO2 kinetics can be considered a marker of the impaired exercise tolerance. The present data could be useful for clinicians who need an objective, quantitative, and longitudinal evaluation of the impairment to be used in the follow-up of these patients as well as in the assessment of therapeutic interventions.
authors.affiliation: Department of Science and Biomedical Technologies, University of Udine, Udine, Italy. bruno.grassi@uniud.it
authors.forename: Bruno
authors.initials: B
authors.lastname: Grassi
authors.forename: Simone
authors.initials: S
authors.lastname: Porcelli
authors.forename: Mauro
authors.initials: M
authors.lastname: Marzorati
authors.forename: Francesca
authors.initials: F
authors.lastname: Lanfranconi
authors.forename: Paola
authors.initials: P
authors.lastname: Vago
authors.forename: Claudio
authors.initials: C
authors.lastname: Marconi
authors.forename: Lucia
authors.initials: L
authors.lastname: Morandi
mesh_terms: D000328:Adult; D004734:Energy Metabolism / Q000502:physiology; D005080:Exercise Test / Q000379:methods; D005260:Female; D024982:Glycogen Phosphorylase, Muscle Form / Q000097:blood / Q000172:deficiency; D006801:Humans; D007700:Kinetics; D008297:Male; D017240:Mitochondrial Myopathies / Q000378:metabolism*; D009135:Muscular Diseases / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D019265:Spectroscopy, Near-Infrared
chemical_list: D024982:Glycogen Phosphorylase, Muscle Form