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Simone Cassani, Giovanna Guidoboni, Aaron Pickrell, Brent A. Siesky, Alon Harris; Quantitative Estimate of Retinal Blood Flow Alterations due to Changes in Ocular Perfusion Pressure and Autoregulatory Function: a Mathematical Model. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2838.
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© ARVO (1962-2015); The Authors (2016-present)
Low ocular perfusion pressure (OPP) and impaired autoregulation (AR) can alter retinal blood flow (RBF) and constitute risk factors for glaucoma. The purpose of this investigation is to describe and quantify RBF alterations due to changes in OPP and AR function.
RBF is described by a mathematical model including five compartments: central retinal artery (CRA), arterioles, capillaries, venules, and central retinal vein (CRV). The flow is time-dependent, driven by systemic pressure and regulated by variable resistances which account for nonlinear effects due to (1) AR, and (2) compression of the lamina cribrosa on CRA and CRV induced by intraocular pressure (IOP). Compartmental compliances are introduced to account for arterial and venous distensibilities. The flow in the compartments is the solution of a system of five nonlinear ordinary differential equations. The system is solved for OPP between 21.7 and 34.2 mmHg, varying independently IOP and mean arterial pressure (MAP), and with and without AR.
OPP and AR strongly influence RBF. With AR, the cardiac cycle RBF average (RBFav) remains around 7.5 1e-4 ml/s as OPP varies. For a given OPP, a difference of at most 2% is found between RBFav values computed by holding MAP constant and varying IOP, and those computed by holding IOP constant and varying MAP. Without AR, the behavior of RBFav with respect to OPP is notably different depending on whether OPP variations are achieved by varying IOP or MAP. The difference can be up to 11%.
With AR, RBFav does not vary notably with OPP, regardless of whether OPP was altered by IOP elevation or MAP reduction. Without AR, RBFav decreases notably with OPP reductions. The reduction rate is linear when MAP is reduced, and nonlinear when IOP is increased. This suggests that low blood pressure and high IOP should be considered as independent risk factors when AR is impaired.
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