Assessment of total retinal blood flow using Doppler Fourier Domain Optical Coherence Tomography during systemic hypercapnia and hypocapnia

The purpose of this study was to investigate changes in total retinal blood flow (RBF) using Doppler Fourier Domain Optical Coherence Tomography (Doppler FD‐OCT) in response to the manipulation of systemic partial pressure of CO(2) (P(ET)CO(2)). Double circular Doppler blood flow scans were captured in nine healthy individuals (mean age ± standard deviation: 27.1 ± 4.1, six males) using the RTVue(™) FD‐OCT (Optovue). P(ET)CO(2) was manipulated using a custom‐designed computer‐controlled gas blender (RespirAct(™)) connected to a sequential gas delivery rebreathing circuit. Doppler FD‐OCT measurements were captured at baseline, during stages of hypercapnia (+5/+10/+15 mmHg P(ET)CO(2)), return to baseline and during stages of hypocapnia (−5/−10/−15 mmHg P(ET)CO(2)). Repeated measures analysis of variance (reANOVA) and Tukey's post hoc analysis were used to compare Doppler FD‐OCT measurements between the various P(ET)CO(2) levels relative to baseline. The effect of P(ET)CO(2) on TRBF was also investigated using linear regression models. The average RBF significantly increased by 15% (P < 0.0001) with an increase in P(ET)CO(2) and decreased significantly by 10% with a decrease in P(ET)CO(2) (P = 0.001). Venous velocity significantly increased by 3.11% from baseline to extreme hypercapnia (P < 0.001) and reduced significantly by 2.01% at extreme hypocapnia (P = 0.012). No significant changes were found in the average venous area measurements under hypercapnia (P = 0.36) or hypocapnia (P = 0.40). Overall, increased and decreased P(ET)CO(2) values had a significant effect on RBF outcomes (P < 0.002). In healthy individuals, altered end‐tidal CO(2) levels significantly changed RBF as measured by Doppler FD‐OCT.