title: Response of inner retinal oxygen extraction fraction to light flicker under normoxia and hypoxia in rat.
abstract: OBJECTIVE
  Oxygen extraction fraction (OEF), defined by the ratio of oxygen metabolism (MO2) to delivery (DO2), determines the level of compensation of MO2 by DO2. In the current study, we tested the hypothesis that inner retinal OEF remains unchanged during light flicker under systemic normoxia and hypoxia in rats due to the matching of MO2 and DO2.
  
  
  METHODS
  Retinal vascular oxygen tension (PO2) measurements were obtained in 10 rats by phosphorescence lifetime imaging. Inner retinal OEF was derived from vascular PO2 based on Fick's principle. Measurements were obtained before and during light flicker under systemic normoxia and hypoxia. The effects of light flicker and systemic oxygenation on retinal vascular PO2 and OEF were determined by ANOVA.
  
  
  RESULTS
  During light flicker, retinal venous PO2 decreased (P < 0.01, N = 10), while inner retinal OEF increased (P = 0.02). Under hypoxia, retinal arterial and venous PO2 decreased (P < 0.01), while OEF increased (P < 0.01). The interaction effect was not significant on OEF (P = 0.52), indicating the responses of OEF to light flicker were similar under normoxia and hypoxia. During light flicker, OEF increased from 0.46 ± 0.13 to 0.50 ± 0.11 under normoxia, while under hypoxia, OEF increased from 0.67 ± 0.16 to 0.74 ± 0.14.
  
  
  CONCLUSIONS
  Inner retinal OEF increased during light flicker, indicating the relative change in DO2 is less than that in MO2 in rats under systemic normoxia and hypoxia. Inner retinal OEF is a potentially useful parameter for assessment of the relative changes of MO2 and DO2 under physiologic and pathologic conditions.
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States.
authors.forename: Pang-yu
authors.initials: PY
authors.lastname: Teng
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States.
authors.forename: Justin
authors.initials: J
authors.lastname: Wanek
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States.
authors.forename: Norman P
authors.initials: NP
authors.lastname: Blair
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States.
authors.forename: Mahnaz
authors.initials: M
authors.lastname: Shahidi
mesh_terms: D000818:Animals; D006940:Hyperemia / Q000378:metabolism / Q000503:physiopathology; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D008027:Light; D008163:Luminescent Measurements / Q000379:methods; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010313:Partial Pressure; D051381:Rats; D020318:Rats, Long-Evans; D012160:Retina / Q000378:metabolism*; D012171:Retinal Vessels / Q000378:metabolism
chemical_list: D010100:Oxygen
keywords: hypoxia; light flicker; oxygen extraction fraction; retina; vascular oxygen tension