title: Regulation of retinal oxygen metabolism in humans during graded hypoxia.
abstract: Animal experiments indicate that the inner retina keeps its oxygen extraction constant despite systemic hypoxia. For the human retina no such data exist. In the present study we hypothesized that systemic hypoxia does not alter inner retinal oxygen extraction. To test this hypothesis we included 30 healthy male and female subjects aged between 18 and 35 years. All subjects were studied at baseline and during breathing 12% O₂ in 88% N₂ as well as breathing 15% O₂ in 85% N₂. Oxygen saturation in a retinal artery (SO₂art) and an adjacent retinal vein (SO₂vein) were measured using spectroscopic fundus reflectometry. Measurements of retinal venous blood velocity using bidirectional laser Doppler velocimetry and retinal venous diameters using a Retinal Vessel Analyzer (RVA) were combined to calculate retinal blood flow. Oxygen and carbon dioxide partial pressure were measured from earlobe arterialized capillary blood. Retinal blood flow was increased by 43.0 ± 23.2% (P < 0.001) and 30.0 ± 20.9% (P < 0.001) during 12% and 15% O₂ breathing, respectively. SO₂art as well as SO₂vein decreased during both 12% O₂ breathing (SO₂art: -11.2 ± 4.3%, P < 0.001; SO₂vein: -3.9 ± 8.5%, P = 0.012) and 15% O₂ breathing (SO₂art: -7.9 ± 3.6%, P < 0.001; SO₂vein: -4.0 ± 7.0%, P = 0.010). The arteriovenous oxygen difference decreased during both breathing periods (12% O2: -28.9 ± 18.7%; 15% O₂: -19.1 ± 16.7%, P < 0.001 each). Calculated oxygen extraction did, however, not change during our experiments (12% O₂: -2.8 ± 18.9%, P = 0.65; 15% O₂: 2.4 ± 15.8%, P = 0.26). Our results indicate that in healthy humans, oxygen extraction of the inner retina remains constant during systemic hypoxia.
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria;
authors.forename: Stefan
authors.initials: S
authors.lastname: Palkovits
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria; Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; and.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Told
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria; Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; and.
authors.forename: Doreen
authors.initials: D
authors.lastname: Schmidl
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria; Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; and.
authors.forename: Agnes
authors.initials: A
authors.lastname: Boltz
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria;
authors.forename: Katarzyna J
authors.initials: KJ
authors.lastname: Napora
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria;
authors.forename: Michael
authors.initials: M
authors.lastname: Lasta
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria;
authors.forename: Semira
authors.initials: S
authors.lastname: Kaya
authors.affiliation: Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; and.
authors.forename: René M
authors.initials: RM
authors.lastname: Werkmeister
authors.affiliation: Department of Ophthalmology, Emergency University Hospital, Bucharest, Romania.
authors.forename: Alina
authors.initials: A
authors.lastname: Popa-Cherecheanu
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria;
authors.forename: Gerhard
authors.initials: G
authors.lastname: Garhöfer
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria; Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; and leopold.schmetterer@meduniwien.ac.at.
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000293:Adolescent; D000328:Adult; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000097:blood; D018592:Cross-Over Studies; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D000860:Hypoxia / Q000097:blood* / Q000503:physiopathology; D017078:Laser-Doppler Flowmetry; D008297:Male; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010313:Partial Pressure; D012039:Regional Blood Flow; D012119:Respiration; D012160:Retina / Q000378:metabolism*; D012161:Retinal Artery / Q000503:physiopathology*; D012169:Retinal Vein / Q000503:physiopathology*; D013997:Time Factors; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: hypoxia; oxygen extraction; retinal blood flow; retinal oxygen metabolism