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Ayda Shahidi, Sunni Patel, John Flanagan, Ou Tan, David Huang, Christopher Hudson, ; Assessment of Total Retinal Blood Flow under Systemic Hypercapnia and Hypocapnia. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4637.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of change in systemic partial pressure of CO2 on total retinal blood flow (TRBF) as measured by Doppler Fourier-domain optical coherence tomography (OCT)
TRBF scans were captured in nine healthy individuals (mean age ± standard deviation: 27±4, 6 males) using the RTVue™ OCT double ring blood flow protocol. Measurements were captured during homeostatic PETCO2 levels, hypercapnia (+5/+10/+15 mmHg PETCO2), back to baseline and hypocapnia (-5/-10/-15 mmHg PETCO2) using a custom-designed computer controlled gas blender (RespirAct™) with a sequential gas delivery rebreathing system. The order for hyper- and hypo-capnia conditions was randomized. Repeated measure analysis of variance (reANOVA) and Tukey’s post-hoc analysis were used to compare Doppler OCT measurements amongst breathing conditions. The effect of end-tidal CO2 on the outcomes was investigated using regression models.
TRBF (45.9 ± 10.9, vs 60.9 ± 12.1 µl/min), superior RBF (24.0 ± 9.3 vs 33.8 ± 9.5 µl/min) , arterial (14.1 ± 2.7 vs 19.9 ± 4.5 mm/s) and venous (12.5 ± 1.7 vs 15.6 ± 1.3 mm/s) velocities were significantly different between baseline measurements and extreme hypercapnia (p<0.0001). There were general trends towards reduced retinal blood flow parameters during hypocapnia but the differences with the baseline, except for the superior arterial vessel area (p=0.006), were not statistically significant. Increased PETCO2 had a significant effect on the outcomes (p<0.002 for all states).
In healthy individuals, a 15% increase in end tidal CO2 significantly raised TRBF and vessel velocity, while, hypocapnia significantly reduced retinal hemodynamics only in the superior arterial area.
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