Continuous, noninvasive, and localized microvascular tissue oximetry using visible light spectroscopy.
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.
Benaron
David A
DA
Biomedical Optics Laboratory, and Department of Pediatrics, Stanford Hospital and Livermore Veterans Affairs Medical Center, Palo Alto, California 94305, USA. dbenaron@stanford.edu
Parachikov
Ilian H
IH
Friedland
Shai
S
Soetikno
Roy
R
Brock-Utne
John
J
van der Starre
Peter J A
PJ
Nezhat
Camran
C
Terris
Martha K
MK
Maxim
Peter G
PG
Carson
Jeffrey J L
JJ
Razavi
Mahmood K
MK
Gladstone
Hayes B
HB
Fincher
Edgar F
EF
Hsu
Christopher P
CP
Clark
F Landon
FL
Cheong
Wai-Fung
WF
Duckworth
Joshua L
JL
Stevenson
David K
DK
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