title: Broadband near-infrared spectroscopy can detect cyanide-induced cytochrome aa3inhibition in rats: a proof of concept study.
abstract: OBJECTIVE
  Clinically available near-infrared spectroscopy (NIRS) devices use two to five wavelengths of light to measure the relative amounts of oxyhemoglobin and deoxyhemoglobin in tissue to determine tissue hemoglobin oxygen saturation (StO2). In addition to StO2, broadband NIRS devices (using hundreds of wavelengths of light) may be able to measure the oxidation state of mitochondrial cytochrome aa3(Cytox) which reflects the subcellular energetic state. We hypothesize that broadband NIRS devices can measure Cytoxindependent of changes in hemoglobin saturation.
  
  
  METHODS
  In this prospective non-randomized study, 20 male Sprague-Dawley rats (300 g) were anesthetized with isoflurane, tracheally intubated, and ventilated with 100% O2containing 2% isoflurane. They were subsequently instrumented with a broadband NIRS device that used a halogen light source coupled to an emitting fibreoptic cable. Three receiving fibreoptic cables were utilized; one analyzed the light source and the other two were directed at the base of the skull. Each receiving fibre was connected to a spectrometer to measure light intensity. Sodium cyanide (NaCN) 5 mg·kg-1iv was injected in order to produce cytochrome aa3reduction. Two to three minutes after injection, oxygen was eliminated and 100% nitrogen (i.e., anoxia) was used for ventilation in order to induce a reduction in both cytochrome aa3and hemoglobin desaturation. Changes in the cytochrome oxidation state and hemoglobin oxygenation were calculated using a broadband algorithm and compared before and after both the NaCN and anoxia interventions.
  
  
  RESULTS
  The NaCN injection resulted in a decrease in median [interquartile range (IQR)] deoxyhemoglobin (-0.014 [-0.29 to -0.005] arbitrary units [AU]; P < 0.001), an increase in oxyhemoglobin (0.013 [-0.011 to 0.031] AU; P < 0.001), and a reduction in cytochrome aa3(-0.015 [-0.020 to -0.011] AU; P < 0.001). Anoxia resulted in an increase in median [IQR] deoxyhemoglobin (0.13 [0.11 to 0.18] AU; P < 0.001), a decrease in oxyhemoglobin (-0.17 [-0.22 to -0.15] AU; P < 0.001), and a reduction in cytochrome aa3(-0.04 [-0.06 to -0.03] AU; P < 0.001).
  
  
  CONCLUSIONS
  Broadband NIRS can effectively measure the directionality of changes in both Cytoxand StO2by uncoupling the cytochrome and hemoglobin signals through inhibition of the electron transport chain and anoxia.
authors.affiliation: Department of Anesthesiology, University of Virginia, P.O. Box 800710-0710, Charlottesville, VA, USA. rht7w@virginia.edu.
authors.forename: Robert H
authors.identifier: http://orcid.org/0000-0001-7262-0653
authors.initials: RH
authors.lastname: Thiele
authors.affiliation: Department of Anesthesiology, University of Virginia, P.O. Box 800710-0710, Charlottesville, VA, USA.
authors.forename: Keita
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Department of Anesthesiology, University of Virginia, P.O. Box 800710-0710, Charlottesville, VA, USA.
authors.forename: Yunzhen
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Anesthesiology, Duke University, Durham, NC, USA.
authors.forename: Raquel R
authors.initials: RR
authors.lastname: Bartz
authors.affiliation: Department of Anesthesiology, University of Virginia, P.O. Box 800710-0710, Charlottesville, VA, USA.
authors.forename: Zhiyi
authors.initials: Z
authors.lastname: Zuo
mesh_terms: D000818:Animals; D003486:Cyanides / Q000008:administration & dosage*; D004195:Disease Models, Animal; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D008297:Male; D010108:Oxyhemoglobins / Q000378:metabolism; D011446:Prospective Studies; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D003486:Cyanides; D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D003576:Electron Transport Complex IV