title: Redox status of cytochrome a,a3: a noninvasive indicator of dysoxia in regional hypoxic or ischemic hypoxia.
abstract: OBJECTIVE
  Multiwavelength near infrared (NIR) spectrophotometry can monitor the redox state of cytochrome a,a3 (cyt a,a3) in vivo. Because cyt a,a3 is the most immediate reductant of oxygen, this technique has been proposed to evaluate tissue oxygenation. The purpose of this study was to examine the relationship between cyt a,a3 oxidation level as an indicator of dysoxia and oxygen uptake (VO2) when oxygen delivery (DO2) was progressively lowered in an in situ vascularly isolated hindlimb.
  
  
  METHODS
  Prospective, randomized, laboratory study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Fourteen pigs.
  
  
  METHODS
  Measurement of critical values for both VO2 and cyt a,a3 oxidation during ischemic and hypoxic hypoxia.
  
  
  RESULTS
  The right hindlimb of anesthetized, paralyzed, and ventilated pigs was subjected to progressive ischemic or hypoxic hypoxia for 100 mins by ten stepwise decreases in DO2. In ischemic hypoxia (n = 7), arterial inflow (Q) from a pump-membrane oxygenator system was lowered from 50 to 0 mL/min, with PaO2 maintained at 100 mm Hg. In hypoxic hypoxia (n = 6), PaO2 was lowered from 100 mm Hg to 0 mm Hg. Hindlimb DO2 was calculated as the product of Q and arterial oxygen content, and VO2 as the product of Q and arteriovenous difference. The cyt a,a3 oxidation level was measured every 10 secs with a four-wavelength spectrophotometer. These parameters were measured 9 mins after each change of DO2. Critical values for both VO2 and cyt a,a3 oxidation level as a function of DO2 were determined in each animal by dual linear regression analysis. In ischemic and hypoxic hypoxia, a strong correlation was found between cyt a,a3 oxidation level and VO2 in both ischemic and hypoxic hypoxia (r2 =.90 and .87, respectively). Hindlimb vascular resistance increased in ischemic hypoxia and decreased in hypoxic hypoxia when DO2 reached critical DO2.
  
  
  CONCLUSIONS
  From these results, we concluded that monitoring the cyt a,a3 redox state by NIR spectrophotometry is, in this experimental setting, a sensitive indicator of dysoxia during regional hypoxic or ischemic hypoxia.
authors: Service de Réanimation Médicale et Maladies Infectieuses, Soins Intensifs de Cardiologie, Centre Hospitalier de Tourcoing, France.
authors: B P
authors: BP
authors: Guery
authors: J
authors: J
authors: Mangalaboyi
authors: P
authors: P
authors: Menager
authors: S
authors: S
authors: Mordon
authors: B
authors: B
authors: Vallet
authors: C
authors: C
authors: Chopin
mesh_terms: D000818:Animals; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006439:Hemodynamics; D006614:Hindlimb / Q000098:blood supply*; D000860:Hypoxia / Q000175:diagnosis / Q000201:enzymology / Q000378:metabolism*; D007511:Ischemia / Q000378:metabolism; D016014:Linear Models; D018482:Muscle, Skeletal / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D011897:Random Allocation; D019265:Spectroscopy, Near-Infrared; D013552:Swine
chemical_list: D003576:Electron Transport Complex IV