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Ioannis K. Petropoulos, Jean-Antoine C. Pournaras, Jean-Luc Munoz, Constantin J. Pournaras; Effect of Carbogen Breathing and Acetazolamide on Optic Disc Po2. Invest. Ophthalmol. Vis. Sci. 2005;46(11):4139-4146. doi: 10.1167/iovs.05-0258.
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purpose. Acetazolamide was previously shown to increase optic disc partial pressure of oxygen (Po 2). The study was conducted to evaluate optic disc Po 2 variations during normoxia, hyperoxia (100% O2), and carbogen breathing (95% O2, 5% CO2), before and after intravenous administration of acetazolamide.
methods. Po 2 measurements were obtained at intervascular areas of the optic disc in nine anesthetized minipigs using oxygen-sensitive microelectrodes (10-μm tip diameter) placed at <50 μm from the optic disc. Po 2 was measured continuously during 10 minutes under normoxia, hyperoxia, or carbogen breathing. Oxygen measurements were repeated under these conditions after intravenous injection of acetazolamide (500-mg bolus).
results. In hyperoxia, optic disc Po 2 increased moderately (ΔPo 2 = 4.81 ± 1.16 mm Hg (mean ± SD; 24%; P < 0.001) after a much larger increase in systemic Pao 2. Carbogen breathing induced a significant increase in both systemic Pao 2 and Paco 2, which resulted in a large increase in optic disc Po 2 (ΔPo 2 = 13.17 ± 2.18 mm Hg; 67%; P < 0.001). Acetazolamide induced a slow and progressive increase in both systemic Paco 2 and optic disc Po 2 (30 minutes ΔPo 2 = 4.24 ± 2.45 mm Hg; 24%; P < 0.04). However, it was when carbogen was simultaneously administered that optic disc Po 2 increased most substantially (ΔPo 2 = 18.91 ± 5.23 mm Hg; 90%; P < 0.002).
conclusions. Carbogen breathing increases optic disc Po 2 significantly in minipigs, more than hyperoxia. The association of acetazolamide injection with carbogen breathing could induce an additional increase in optic disc Po 2 through the effect of higher systemic Paco 2.
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