Simulated impact of vascular network structure heterogeneity on retinal tissue oxygenation

Abstract

Purpose : A theoretical model of the human retina is simulated using two different vascular network geometries to predict the impact of heterogeneity in vascular network structure on retinal tissue oxygenation.

Methods : Two different branches (Branch 1) and (Branch 2) from a published theoretical model of the human retinal vasculature are used to investigate the role of vessel network geometry on tissue oxygenation. The vascular network is modeled as a combined heterogeneous representation of retinal arterioles and compartmental representation of capillaries, small venules, and large venules. A Green’s function method is used to model oxygen transport in the arterioles, and a Krogh cylinder model is used in the capillaries and venules. Identical input arterial blood saturation (0.92), arteriolar pressure drop (16 mmHg), and arteriolar diameters by vessel order (117, 73, 44, 32, and 22 µm) are assumed for both branches. Given these inputs, we created a mathematical model to predict blood vessel and arteriolar tissue PO₂ for both retinal vascular networks.

Results : Figure 1 depicts the model-predicted levels of vessel and arteriolar tissue PO₂ for each network. In Figure 1 (bottom), the percentage of arteriolar tissue exhibiting a PO₂ level less than a given value (PO₂ threshold) is given for Branch 1 (blue) and Branch 2 (red). As indicated by points A and B, 20% of the arteriolar tissue in Branch 1 has a PO₂ less than 20 mmHg, while only 6% of the arteriolar tissue in Branch 2 has a PO₂ less than 20 mmHg. The model also predicts a higher oxygen extraction fraction in Branch 2 than Branch 1 (Figure 1, top and middle). The difference in mean arteriolar tissue PO₂ between the two networks is predicted to increase as the level of oxygen demand is increased (not depicted).

Conclusions : The mathematical model used in this study demonstrates the impact of heterogeneity of vascular network structure on the oxygenation of retinal tissue. Even with identical initial conditions for saturation, pressure drop, and diameter, variations in network geometry lead to significantly different regions of low PO₂, indicating a wide range of potential oxygenation outcomes for individual patients. This study therefore demonstrates that regional heterogeneity in vessel branching architecture may significantly impact oxygen saturation and ultimately retinal ganglion cell health and functionality.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.