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Shaohua Pi, Tristan Hormel, Xiang Wei, William O. Cepurna, Bingjie Wang, John C Morrison, Yali Jia; Blood Oxygen Saturation in Retinal Microcirculation. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2536.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate blood oxygen saturation (sO2) in retinal microcirculation, as well as its responses to hypoxia and hyperoxia in rats using visible-light optical coherence tomography (vis-OCT).
A 1.7 µm axial resolution, 50 kHz sampling rate, fiber-based vis-OCT system centered at 560 nm was built and used to image the retinas of brown Norway rats (14 weeks old, n=6). The animals were initially anesthetized with 2.5% isoflurane mixed with inhalation gas. During imaging, the oxygen concentration in the inhalation gas was regulated from normoxia (21% O2), to hypoxia (15% O2), to hyperoxia (100% O2), and back to normoxia. Two repeated volumetric raster scans were collected near the optic disc with a field of view of 2 × 2-mm at each inhalation condition. The laminar vascular/capillary plexus en face images were registered and averaged at all conditions to improve the extraction of capillary segments. The spectroscopic signals were then averaged along each capillary segment and fit to a model to determine sO2 of that capillary segment (Fig. 1).
The sO2 measurements in each plexus were quite repeatable, with inter-scan repeatability (pooled standard deviation) calculated as 1.9% (Fig. 2A). The measured retinal arterial sO2 correlated well with the systemic sO2 (Fig. 2B). The sO2 in veins was lower than that in arteries and changed most dramatically from a low of 52.5% ± 5.7% at hypoxia, to a high of 85.3% ± 6.0% at hyperoxia (Fig. 2 B-C). The averaged sO2 in the arterial capillary of superficial vascular plexus (SVP-AC), intermediate capillary plexus (ICP) and deep capillary plexus (DCP) were lower than that in arteries, with a decrease of ~2% (p-value< 0.01) at hypoxia and an increase of ~4% (p-value<0.01) at hyperoxia from ~65% at normoxia (Fig. 2C). The sO2 decreased gradually with respect to increase of capillary order (determined by the number of downstream capillary segments) in arterial capillaries of superficial vascular plexus (Fig. 2D), indicating the release of oxygen along these capillaries. The sO2 in fifth order capillaries was maintained at almost the same level as that in the ICP and DCP, indicating equilibrium oxygen exchange at these places.
The blood oxygen saturation in both major vessels and capillaries in retinal circulation can be noninvasively assessed with vis-OCT. Capillaries were more resistant to temporary hypoxia/hyperoxia regulation than major vessels.
This is a 2020 ARVO Annual Meeting abstract.
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