title: Continuous, noninvasive, and localized microvascular tissue oximetry using visible light spectroscopy.
abstract: BACKGROUND
  The authors evaluated the ability of visible light spectroscopy (VLS) oximetry to detect hypoxemia and ischemia in human and animal subjects. Unlike near-infrared spectroscopy or pulse oximetry (SpO2), VLS tissue oximetry uses shallow-penetrating visible light to measure microvascular hemoglobin oxygen saturation (StO2) in small, thin tissue volumes.
  
  
  METHODS
  In pigs, StO2 was measured in muscle and enteric mucosa during normoxia, hypoxemia (SpO2 = 40-96%), and ischemia (occlusion, arrest). In patients, StO2 was measured in skin, muscle, and oral/enteric mucosa during normoxia, hypoxemia (SpO2 = 60-99%), and ischemia (occlusion, compression, ventricular fibrillation).
  
  
  RESULTS
  In pigs, normoxic StO2 was 71 +/- 4% (mean +/- SD), without differences between sites, and decreased during hypoxemia (muscle, 11 +/- 6%; P < 0.001) and ischemia (colon, 31 +/- 11%; P < 0.001). In patients, mean normoxic StO2 ranged from 68 to 77% at different sites (733 measures, 111 subjects); for each noninvasive site except skin, variance between subjects was low (e.g., colon, 69% +/- 4%, 40 subjects; buccal, 77% +/- 3%, 21 subjects). During hypoxemia, StO2 correlated with SpO2 (animals, r2 = 0.98; humans, r2 = 0.87). During ischemia, StO2 initially decreased at -1.3 +/- 0.2%/s and decreased to zero in 3-9 min (r2 = 0.94). Ischemia was distinguished from normoxia and hypoxemia by a widened pulse/VLS saturation difference (Delta < 30% during normoxia or hypoxemia vs. Delta > 35% during ischemia).
  
  
  CONCLUSIONS
  VLS oximetry provides a continuous, noninvasive, and localized measurement of the StO2, sensitive to hypoxemia, regional, and global ischemia. The reproducible and narrow StO2 normal range for oral/enteric mucosa supports use of this site as an accessible and reliable reference point for the VLS monitoring of systemic flow.
authors.affiliation: Biomedical Optics Laboratory, and Department of Pediatrics, Stanford Hospital and Livermore Veterans Affairs Medical Center, Palo Alto, California 94305, USA. dbenaron@stanford.edu
authors.forename: David A
authors.initials: DA
authors.lastname: Benaron
authors.forename: Ilian H
authors.initials: IH
authors.lastname: Parachikov
authors.forename: Shai
authors.initials: S
authors.lastname: Friedland
authors.forename: Roy
authors.initials: R
authors.lastname: Soetikno
authors.forename: John
authors.initials: J
authors.lastname: Brock-Utne
authors.forename: Peter J A
authors.initials: PJ
authors.lastname: van der Starre
authors.forename: Camran
authors.initials: C
authors.lastname: Nezhat
authors.forename: Martha K
authors.initials: MK
authors.lastname: Terris
authors.forename: Peter G
authors.initials: PG
authors.lastname: Maxim
authors.forename: Jeffrey J L
authors.initials: JJ
authors.lastname: Carson
authors.forename: Mahmood K
authors.initials: MK
authors.lastname: Razavi
authors.forename: Hayes B
authors.initials: HB
authors.lastname: Gladstone
authors.forename: Edgar F
authors.initials: EF
authors.lastname: Fincher
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Hsu
authors.forename: F Landon
authors.initials: FL
authors.lastname: Clark
authors.forename: Wai-Fung
authors.initials: WF
authors.lastname: Cheong
authors.forename: Joshua L
authors.initials: JL
authors.lastname: Duckworth
authors.forename: David K
authors.initials: DK
authors.lastname: Stevenson
mesh_terms: D000818:Animals; D006801:Humans; D008027:Light; D008833:Microcirculation / Q000737:chemistry* / Q000378:metabolism*; D009092:Mucous Membrane / Q000098:blood supply / Q000378:metabolism; D009132:Muscles / Q000098:blood supply / Q000378:metabolism; D010092:Oximetry / Q000379:methods*; D013057:Spectrum Analysis / Q000379:methods; D013552:Swine