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Justin Wanek, Pang-yu Teng, Norman P. Blair, Mahnaz Shahidi; Global Inner Retinal Metabolic Rate of Oxygen During Hypoxia in Rat. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4990.
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Insufficient oxygen delivery and/or consumption can adversely affect retinal function. Therefore, it is important to investigate the effect of hypoxia on retinal oxygen metabolism. The purpose of this study is to report measurements of global inner retinal metabolic rate of oxygen (MO2) by combined oxygen tension (PO2) and blood flow (BF) imaging in rat under systemic normoxia and hypoxia.
Global inner retinal MO2 measurements were obtained in 2 groups of 8 rats ventilated with 10% (hypoxia) or 21% (normoxia) oxygen. Systemic arterial blood gas tensions (PaO2, PaCO2), pH, mean blood pressure (BP), and heart rate (HR) were recorded. PO2 in all major retinal arteries and veins was measured using our phosphorescence lifetime imaging system and the arteriovenous oxygen content difference (ΔO2) was calculated. Blood velocity was determined by imaging the intravascular motion of fluorescent microspheres and venous diameter was measured from red-free retinal images, providing calculation of BF in all veins. Global inner retinal MO2 was determined based on venous BF and ΔO2 using Fick’s equation. Unpaired Student’s t-test was used for comparative statistical analysis.
Systemic physiological and retinal oxygenation parameters under normoxia and hypoxia are summarized in Table 1. Under hypoxia, mean ΔO2 was significantly lower than under normoxia (p < 0.001). Mean venous BF was similar under hypoxia and normoxia (p = 0.93). Global inner retinal MO2 was significantly lower under hypoxia (186 ± 112 nL O2/min) compared to normoxia (543 ± 190 nL O2/min) (p < 0.001).
Global inner retinal MO2 in rat was significantly lower during hypoxia as compared to normoxia, suggesting insufficient vascular regulation in the inner retina to fully compensate for the reduced oxygen delivery at the level of hypoxia studied.
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