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Angelina Duan, Phillip Bedggood, Andrew Metha, Bang V Bui; Imaging the response of the human retinal microvasculature to hyperoxia and hypercapnia. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5914.
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© ARVO (1962-2015); The Authors (2016-present)
To quantify changes in diameter in small (<25μm) blood vessels in response to systemic gas breathing perturbation
The foveal microvascular network was imaged in 3 healthy subjects with a full-frame adaptive optics ophthalmoscope with informed consent as per the Declaration of Helsinki. Each 1.25° imaged region was selected to contain a "major" arteriole or venule (≈15-25μm diameter) and associated branches of varying size. Five image sequences (200fps, 25 frames) separated by resting periods of 3 mins were collected using a 593±23 nm (FWHM) imaging light at a) room air (PETO2 114.2±1.2mmHg, PETCO2 36.5±0.3mmHg), b) isocapnic hyperoxia (PETO2 473.3±5.5mmHg, PETCO2 35.7±0.4mmHg, c) return to room air and d) isoxic hypercapnia (PETO2 116.7±1.5mmHg, PETCO2 44.9±0.3mmHg). Vessel diameter was measured using custom Matlab software based on thresholding.
Differential gas-breathing response of 24 vessel segments (12 arterioles and 12 venules across 6 imaged regions) were measured. Statistical analysis showed a small vasoconstriction in response to hyperoxia (-1.7±1.4%, p=0.03, two-tailed paired t-test) and a larger vasodilation in response to hypercapnia (3.2±1.4%, p=0.02). There was a tendency for arterioles (-3.9±1.1%) to respond to hyperoxia more than venules, but this did not reach significance (0.6±2.4%, p=0.11). Arterioles (3.1±1.6%) and venules (4.1±2.3%) responded similarly to hypercapnia (p=0.57). Analysis of vessel size suggests that segments >10µm in diameter (hyperoxia -4.1±1.6%, hypercapnia 5.8±2.0%) responded more than segments <10µm (hyperoxia 0.8±2.1%, hypercapnia 1.2±2.3%), however these differences were not statistically significant at the 95% level (hyperoxia p=0.08, hypercapnia p=0.07).
Gas-induced vasoreactivity in the smallest vessels of the human retina can be detected with adaptive optics. The direction and magnitude of change is consistent with measurements made on larger vessels from other studies. There is a trend that arterioles and larger vessels are more responsive than venules or smaller vessels. The magnitude of response to systemic gas perturbations seems to be smaller than the response to flicker stimulation, reported previously by the same authors for vessels of similar caliber.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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