Retinal arteriolar vascular reactivity to incremental changes in hyperoxic stimuli during isocapnia

Abstract

Abstract Purpose To determine the relationship between the magnitude of retinal arteriolar vascular reactivity and incremental changes in hyperoxic stimuli whilst maintaining isocapnia. Methods Twelve healthy, young adults (mean age 27 years, SD 4) participated in a gas protocol consisting of 4 phases at varying fractional expired oxygen levels (FeO2): baseline (15%), hyperoxia I (40%), hyperoxia II (65%), and recovery (15%). End‐tidal carbon dioxide (ETCO2) was maintained at isocapnia throughout the experiment. Retinal arteriolar diameter, blood velocity, and blood flow were assessed non‐invasively using the Canon Laser Blood Flowmeter during each of these phases. Results Repeated measures ANOVA showed that there were significant influences of incremental changes in FeO2 on retinal arteriolar diameter (p<0.0001), blood velocity (p<0.0001), and blood flow (p<0.0001). Paired t‐tests of these retinal hemodynamic parameters during each phase in the gas sequence showed they were significantly different (p<0.05) from each other, with the exception of baseline and recovery values. Incremental increases in FeO2 caused a linear decrease in group mean arteriolar diameter (R2 = 1, p = 0.002), group mean blood velocity (R2 = 0.9968, p = 0.04), and group mean blood flow (R2 = 0.9982, p= 0.03). Conclusion Isocapnic hyperoxia elicits vasoconstriction and the reduction of retinal arteriolar diameter, velocity and blood flow in a dose‐dependent manner over the range of FeO2 explored in this study. Commercial interest