title: Impaired Skeletal Muscle Oxygenation and Exercise Tolerance in Pulmonary Hypertension.
abstract: BACKGROUND
  Limb muscle dysfunction is documented in pulmonary arterial hypertension (PAH), but little is known regarding muscle oxygen (O2) supply and its possible effects on exercise tolerance in PAH.
  
  
  METHODS
  Ten patients with PAH and 10 matched controls underwent progressive maximal cardiopulmonary exercise test, voluntary and nonvolitional dominant quadriceps muscle strength measures, and nondominant quadriceps biopsy to assess maximal oxygen uptake, muscle function, and lower limb fiber type and capillarity, respectively. Both groups then performed normoxic and hyperoxic submaximal intensity exercise protocol at the same absolute workload during which muscle O2 supply was assessed by measuring changes in myoglobin-deoxyhemoglobin level (Δ[Mb-HHb]) and tissue oxygenation index in the dominant quadriceps using near-infrared spectroscopy. Changes in cardiac output, estimated systemic O2 delivery, and systemic O2 saturation were also assessed noninvasively throughout both submaximal exercises.
  
  
  RESULTS
  Patients with PAH displayed lower maximal oxygen uptake (P < 0.01), skeletal muscle strength (P < 0.05), and capillarity (P = 0.01). Throughout the normoxic submaximal exercise protocol, Δ[Mb-HHb] (P < 0.01) was higher whereas changes in tissue oxygenation index (P < 0.01) and systemic O2 saturation (P = 0.01) were lower in patients with PAH compared with those in controls. Conversely, changes in cardiac output and estimated systemic O2 delivery were similar between groups. Muscle oxygenation remained unchanged with O2 supplementation. Among variables known to influence tissue oxygenation, only quadriceps capillarity density correlated with Δ[Mb-HHb] (r = -0.66, P < 0.01), which in turn correlated with maximal oxygen uptake (r = -0.64, P < 0.01), 6-min walked distance (r = -0.74, P = 0.01), and both voluntary (r = -0.46, P = 0.04) and nonvolitional (r = -0.50, P = 0.02) quadriceps strength.
  
  
  CONCLUSIONS
  Capillary rarefaction within the skeletal muscle influences exercise tolerance and quadriceps strength at least partly through impaired muscle oxygen supply in PAH.
authors.affiliation: 1Pulmonary Hypertension Research Group, Québec Heart and Lungs Institute Research Center, Laval University, Québec City, Québec, CANADA; and 2Québec Heart and Lungs Institute Research Center, Laval University, Québec City, Québec, CANADA.
authors.forename: Simon
authors.initials: S
authors.lastname: Malenfant
authors.forename: François
authors.initials: F
authors.lastname: Potus
authors.forename: Vincent
authors.initials: V
authors.lastname: Mainguy
authors.forename: Evelyne
authors.initials: E
authors.lastname: Leblanc
authors.forename: Mathieu
authors.initials: M
authors.lastname: Malenfant
authors.forename: Fernanda
authors.initials: F
authors.lastname: Ribeiro
authors.forename: Didier
authors.initials: D
authors.lastname: Saey
authors.forename: François
authors.initials: F
authors.lastname: Maltais
authors.forename: Sébastien
authors.initials: S
authors.lastname: Bonnet
authors.forename: Steeve
authors.initials: S
authors.lastname: Provencher
mesh_terms: D000328:Adult; D002197:Capillary Action; D002302:Cardiac Output; D017079:Exercise Tolerance; D005260:Female; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D006976:Hypertension, Pulmonary / Q000378:metabolism / Q000503:physiopathology*; D035002:Lower Extremity / Q000098:blood supply / Q000503:physiopathology; D008297:Male; D008833:Microcirculation; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D009211:Myoglobin / Q000097:blood; D010101:Oxygen Consumption; D052097:Quadriceps Muscle / Q000098:blood supply / Q000503:physiopathology
chemical_list: D006454:Hemoglobins; D009211:Myoglobin; C100003:deoxyhemoglobin