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P.-J. Bernard, V. Vucea, V. Diaconu; The Optic Nerve Micro-Capillaries Blood Oxygenation Mechanisms in Correlation With Systemic Arterial Blood Oxygenation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2343.
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The main objective of this study was to understand the normal metabolism of the eye in function of the blood oxygenation state in the optic nerve micro-capillaries structures. Specifically, it was proposed to define the ischemic circumstances of these structures from blood oxygenation measurements.
Six young healthy non-smokers subjects participated in the study. Using a continuous and real time spectro-reflectometry technique (Diaconu 2009), we recorded the blood oxygenation changes in the optic nerve micro-capillaries structures, in function of arterial blood oxygenation variations during conditions of hypo-oxygenation, created with a Medisoft ventilation system. An experimental session consisted of breathing 21% O2 ambiant air for one minute, 15% oxygen hypoxic breathing condition for 3 minutes, then 21% O2 ambiant air for one minute. The heart rate and the systemic blood oxygenation changes were monitored with a pulse oxy-meter on the finger. The main interest of the study was to quantify the range and the latency time of blood oxygenation variations, in order to understand the normal vascular system performance.
The results show that the blood oxygenation at the optic nerve level decreases 30 seconds after the 15 % O2 ventilation condition is established. A fall of 6% in systemic arterial blood oxygenation induces an increase of 10% of heart rate and a simultaneous reduction of 5 % in blood oxygenation in the optic nerve head.
This data does not demonstrate a blood oxygenation regulation mechanism in the optic nerve head micro-capillaries. Hypoxia leads indeed to oxygenation decrease even in the optic nerve which is known to be very sensible to oxygenation privation. This technique could be used further to investigate modifications of oxygenation metabolism for instance in glaucomatous patients.
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