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Kalpana Rose, Susith Kulasekara, Christopher Hudson; Inter-visit repeatability of retinal blood oxygen saturation and total retinal blood flow measurements under conditions of hypoxia, hyperoxia and normoxia in healthy individuals. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4409.
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© ARVO (1962-2015); The Authors (2016-present)
The development of a prototype Doppler spectral domain optical coherence tomography (SD-OCT) blood flow technology and hyperspectral retinal imaging represent a significant advance in ocular imaging capabilities. In this study, SD-OCT derived total retinal blood flow (TRBF) measurements as well as the oxygen saturation (SO2) of major retinal vessels were validated and calibrated in human volunteers using a novel and exact provocation technique (RespirAct) that allows the precise control of the end-tidal partial pressure of oxygen (PETO2). We hypothesis that an increase in arterial O2 tension will decrease the TRBF and increase the retinal oxygen saturation; and vice versa should occur when arterial O2 tension decreases. Between visit repeatability of the TRBF and retinal blood SO2 were also studied.
One eye of 11 young healthy subjects was randomly chosen for the study. TRBF and retinal SO2 measurements were obtained under conditions of normoxia, hyperoxia and hypoxia. The order of hyperoxia and hypoxia was be randomized between subjects. The measurements were repeated after a week interval. Pulse rate, blood pressure and intraocular pressure were also measured.
The preliminary results shows that as the arterial PETO2 was increased from baseline (PETO2=100mmHg) to 200 and 300mmHg, the TRBF significantly reduced (reANOVA, P=0.04) from 36.08 μl/min (+4.78) to 33.27 μl/min (+5.06) and 28.23 μl/min (+2.84). Lowering the arterial PETO2, from baseline to 80, 60 and 50mmHg, TRBF significantly increased (reANOVA, p=0.02) from 32.40 μl/min (+3.38) to 35.51 μl/min (+1.76), 41.37 μl/min (+1.04) and 46.18 μl/min (+0.72) with simultaneous reduction in the arterial blood SO2 content from 96.75 % (+ 0.71) to 94.38% (+ 0.16), 92.06% (+ 1.41), and 88.82% (+ 0.35) respectively. The coefficient of repeatability (COR) of TRBF and retinal arterial blood SO2 values were 2.13 μl/min and 3.34 % respectively.
As hypothesised, increase in arterial PETO2 from baseline decreases the TRBF. Conversely, decreasing the arterial PETO2 from baseline increases the TRBF with simultaneous reduction in the retinal arterial blood SO2. Retinal blood flow and oxygen saturation measurements performed under safe levels of hypoxia and hyperoxia were repeatable in healthy adults.
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