Retinal oximetry measures systemic hypoxia in central nervous system vessels in chronic obstructive pulmonary disease.
BACKGROUND
Determination of the blood oxyhemoglobin saturation in the retinal vessels of the eye can be achieved through spectrophotometric retinal oximetry which provides access to the state of oxyhemoglobin saturation in the central nervous system circulation. The purpose of this study was to test the capability of the Oxymap T1 oximeter to detect systemic hypoxemia and the effect of supplemental oxygen on retinal vessel oxyhemoglobin saturation.


METHODS
Oxygen saturation of hemoglobin in retinal arterioles and venules was measured in 11 subjects with severe chronic obstructive pulmonary disease (COPD) on long term oxygen therapy. Measurements were made with and without their daily supplemental oxygen. Eleven healthy age and gender matched subjects were measured during ambient air breathing for comparison of oxyhemoglobin saturation in retinal arterioles and venules. Retinal arteriolar oxyhemoglobin saturation in COPD subjects inspiring ambient air was compared with finger pulse oximetry and blood samples from radial artery.


RESULTS
COPD subjects had significantly lower oxyhemoglobin saturation during ambient air breathing than healthy controls in both retinal arterioles (87.2%±4.9% vs. 93.4%±4.3%, p = 0.02; n = 11) and venules (45.0%±10.3% vs. 55.2%±5.5%, p = 0.01). Administration of their prescribed supplemental oxygen increased oxyhemoglobin saturation in retinal arterioles (87.2%±4.9% to 89.5%±6.0%, p = 0.02) but not in venules (45.0%±10.3% to 46.7%±12.8%, p = 0.3). Retinal oximetry values were slightly lower than radial artery blood values (mean percentage points difference = -5.0±5.4, 95% CI: -15.68 to 5.67) and finger pulse oximetry values (-3.1±5.5, 95% CI: -14.05 to 7.84).


CONCLUSIONS
The noninvasive Oxymap T1 retinal oximetry detects hypoxemia in central nervous system vessels in patients with severe COPD compared with healthy controls. The instrument is sensitive to changes in oxygen breathing but displays slightly lower measures than finger pulse oximetry or radial artery measures. With further technological improvement, retinal oximetry may offer noninvasive "on-line" measurement of oxygen levels in central circulation in general anesthesia and critically ill patients.
University of Iceland, Reykjavik, Iceland.|Department of Ophthalmology, The National University Hospital of Iceland, Reykjavik, Iceland.|Department of Anesthesiology, Landspítali-The National University Hospital of Iceland, Reykjavik, Iceland.
Thorunn Scheving
http://orcid.org/0000-0003-4217-7050
TS
Eliasdottir
Department of Ophthalmology, The National University Hospital of Iceland, Reykjavik, Iceland.
David
D
Bragason
University of Iceland, Reykjavik, Iceland.
Sveinn Hakon
SH
Hardarson
School of Nursing, Duke University, Durham, North Carolina, United States of America.
Charles
C
Vacchiano
Department of Respiratory Medicine and Sleep (E7), Landspítali-The National University Hospital of Iceland, Reykjavík, Iceland.
Thorarinn
T
Gislason
Department of Ophthalmology, The National University Hospital of Iceland, Reykjavik, Iceland.
Jona Valgerdur
JV
Kristjansdottir
University of Iceland, Reykjavik, Iceland.
Gudrun
G
Kristjansdottir
University of Iceland, Reykjavik, Iceland.|Department of Ophthalmology, The National University Hospital of Iceland, Reykjavik, Iceland.
Einar
E
Stefánsson
D000368:Aged; D000369:Aged, 80 and over; D001160:Arterioles / Q000378:metabolism; D002490:Central Nervous System / Q000378:metabolism*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D008297:Male; D010092:Oximetry / Q000379:methods; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D010108:Oxyhemoglobins / Q000378:metabolism; D029424:Pulmonary Disease, Chronic Obstructive / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D012171:Retinal Vessels / Q000378:metabolism*; D014699:Venules / Q000378:metabolism
D010108:Oxyhemoglobins; D010100:Oxygen