Abstract
Cerebral and retinal blood flow are dependent on local neuronal activity. Several studies quantified the increase in cerebral blood flow and oxygen consumption during activity. In the present study we investigated the relation between changes in retinal blood flow and oxygen extraction during stimulation with diffuse luminance flicker and the influence of breathing gas mixtures with different fractions of O2 (FiO2; 100% 15% and 12%). Twenty-four healthy subjects were included. Retinal blood flow was studied by combining measurement of vessel diameters using the Dynamic Vessel Analyser with measurements of blood velocity using laser Doppler velocimetry. Oxygen saturation was measured using spectroscopic reflectometry and oxygen extraction was calculated. Flicker stimulation increased retinal blood flow (57.7 ± 17.8%) and oxygen extraction (34.6 ± 24.1%; p < 0.001 each). During 100% oxygen breathing the response of retinal blood flow and oxygen extraction was increased (p < 0.01 each). By contrast, breathing gas mixtures with 12% and 15% FiO2 did not alter flicker–induced retinal haemodynamic changes. The present study indicates that at a comparable increase in blood flow the increase in oxygen extraction in the retina is larger than in the brain. During systemic hyperoxia the blood flow and oxygen extraction responses to neural stimulation are augmented. The underlying mechanism is unknown.
Highlights
In the present study we investigated the response of retinal blood flow and retinal oxygen extraction to diffuse luminance flicker in healthy subjects
To the best of our knowledge this is the first study in humans to quantify retinal oxygen extraction in response to stimulation with diffuse luminance flicker
Our data indicate that an increase in retinal blood flow of approximately 55% is associated with an increase in retinal oxygen extraction of approximately 35%
Summary
To the best of our knowledge no previous study has characterized the effects of retinal stimulation with diffuse luminance flicker on retinal oxygen extraction in humans. When oxygen is delivered via inhalation the rat retina reacts with pronounced vasoconstriction and the response to flicker light stimulation is fully preserved[17]. We have recently investigated the effect of diffuse luminance flicker on blood flow under FiO2 of 100% and found an augmented blood flow increase during 100% oxygen breathing due to a so far unknown mechanism[18]. In the present study we investigated the response of retinal blood flow and retinal oxygen extraction to diffuse luminance flicker in healthy subjects. We investigated whether these responses are modified by inhaling gases with different FiO2 inducing either systemic hyperoxia or hypoxia
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