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L. Wang, G. Cull, B. Fortune, G. A. Cioffi; Dual Size Mixture of Microspheres for Sequential Ocular Blood Flow Measurement in Rats. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2294.
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The optimal microsphere size for measurement of retinal and choroidal blood flow (BF) in rats was determined to be 8 µm and 10 µm, respectively; the optimal dose to be 2.5 million and 0.5 million, respectively (PubMed17069799). The purpose of the current study was to evaluate the stability of BF measurements over time under control conditions using a microsphere mixture of the two optimized sizes/doses, in order to establish a method for the study of BF autoregulation in rat.
In seven isofluorane anesthetized and mechanically ventilated adult Brown Norway rats, the blood pressure and end tidal CO2 partial pressure (EtCO2) was continuously monitored and maintained within normal ranges. A mixture of fluorescent microspheres with a size/dose/color of 8 µm/2.5 million/yellow and 10 µm/0.5 million/red was administered into the left ventricle by trans-diaphragm injection. Under similar experimental conditions, approximately 5 minutes after the first injection, a second microspheres mixture with the same sizes and doses, but different colors (green/blue), was injected. A reference arterial blood sample was drawn from one femoral artery for one minute starting from the onset of each microsphere injection. The total number of each colored microspheres (Mt) entrapped in the retina (8 µm) and in the choroid (10 µm), and the microsphere concentration of each of four different colors in the reference blood (Mr) was quantified with an image analysis system. The BF in the retina and choroid (µl/min per tissue) during each of the measurements was determined by each colored microspheres (Mt/Mr).
Table shows the BF values between two eyes and between two measurements. Statistical analysis showed no significant BF differences between the two eyes, nor between sequential measurements.
The double-size and double-dose microspheres mixture can reliably estimate the retinal and choroidal BF in rats for at least two sequential measurements at a time interval studied.
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