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Z. He, A. J. Vingrys, B. V. Bui; Characterization of Blood Flow Autoregulation in Rat Eyes. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2686.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the autoregulation of ocular blood flow across a wide range of ocular perfusion pressure (OPP).
In 4 groups of anaesthetized (60:5 mg/kg ketamine:xylazine im.) Long-Evan rats, OPP challenge was induced by manipulating either mean arterial pressure (MAP) or intraocular pressure (IOP). MAP was increased to ~170 mmHg by ligation of celiac and left renal artery, and gradually reduced to ~20 mmHg either volumetrically (exsanguination, n = 8) or pharmacologically (sodium nitroprusside (SNP), iv. n = 5) while IOP was held at 10 mmHg. In another 2 groups, step-wise IOP elevation (from 10 to 120 mmHg, 5 mmHg step / 3 min) was induced by anterior chamber cannulation while animals were kept at normal (~110 mmHg, sham iv. n = 6) or high MAP (~150 mmHg, Angiotensin II iv. n = 6). Blood pressure was monitored throughout the experiments via femoral artery cannulation. Ocular blood flow was assessed by laser-Doppler flowmetry with a needle probe in the vitreous chamber. The relationship between relative blood flow (percentage of baseline condition) and OPP was modeled using a polynomial. Autoregulatory capacity, defined as the OPP range to maintain ± 20% of baseline blood flow, was analyzed with non-parametric bootstrap and compared between different methods of OPP variation.
The relationship between ocular blood flow and OPP determined by SNP infusion (n = 5) could not be described with a linear regression, indicating for autoregulation. Blood flow remained within ± 20% of baseline for OPPs between 97.5 - 50.0 mmHg (range 47.5, 95%CL 15.0 - 62.5 mmHg). This autoregulatory range was significantly reduced (27.5, 95%CL 25.0 - 30.0 mmHg, p < 0.05) when OPP was modified by exsanguination (5ml or 27% of total blood volume, n = 8). Additionally, the autoregulatory range was diminished when OPP challenge was achieved by IOP elevation at normal (range 20.0, 95%CL 15.0 - 30.0 mmHg, n = 6, p < 0.05) and high MAP (range 20.0, 95%CL 15.0 - 20.0 mmHg, n = 6, p < 0.05).
Ocular blood flow in rats showed autoregulation for MAP-induced OPP modulation between 97.5 - 50 mmHg by infusion of SNP, consistent with that reported in rat cortex (Chemtob et al. Circ Res. 1990). IOP-induced challenge in the absence of SNP reduced autoregulatory capacity.
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