Abstract
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 CO2 (PETCO2). 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). PETCO2 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 PETCO2), return to baseline and during stages of hypocapnia (−5/−10/−15 mmHg PETCO2). Repeated measures analysis of variance (reANOVA) and Tukey's post hoc analysis were used to compare Doppler FD‐OCT measurements between the various PETCO2 levels relative to baseline. The effect of PETCO2 on TRBF was also investigated using linear regression models. The average RBF significantly increased by 15% (P < 0.0001) with an increase in PETCO2 and decreased significantly by 10% with a decrease in PETCO2 (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 PETCO2 values had a significant effect on RBF outcomes (P < 0.002). In healthy individuals, altered end‐tidal CO2 levels significantly changed RBF as measured by Doppler FD‐OCT.
Highlights
Altered retinal hemodynamics and disturbance of blood flow regulation are commonly reported in ocular pathologies such as glaucoma and diabetic retinopathy; the overall understanding of these changes remains controversial
Group mean total retinal blood flow (TRBF) significantly increased by 15% (F = 65.77, P < 0.0001) as a result of an increase in baseline PETCO2 to the most extreme hypercapnia (PETCO2 +15 mmHg)
This study, in agreement with previous studies (Harris et al 1995; Tayyari et al 2009), demonstrated that hypercapnia causes an increase in retinal blood flow (RBF) and has a significant positive association with RBF in healthy individuals
Summary
Altered retinal hemodynamics and disturbance of blood flow regulation are commonly reported in ocular pathologies such as glaucoma and diabetic retinopathy; the overall understanding of these changes remains controversial. The development of noninvasive techniques has provided useful information on retinal hemodynamics including vessel diameter, blood velocity, and blood flow in both health and disease. Techniques such as Color Doppler imaging (CDI) can provide information on pulsatile blood flow but since the vessel diameters cannot be quantified with this technique, total retinal blood flow cannot be determined. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.
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