Purpose: This study uses a theoretical model to investigate the response of retinal blood flow to changes in tissue oxygen demand. The study is motivated by the need for a better understanding of metabolic flow regulation mechanisms in health and disease.
Methods: A mathematical model is used to calculate retinal blood flow for different levels of tissue oxygen demand in the presence or absence of regulatory mechanisms. The model combines a compartmental view of the retinal vasculature and a Krogh cylinder description for oxygen delivery to retinal tissue.
Results: The model predicts asymmetric behavior in response to changes in tissue oxygen demand. When all regulatory mechanisms are active, the model predicts a 6% decrease in perfusion when tissue oxygen demand is decreased by 50% and a 23% increase in perfusion when tissue oxygen demand is increased by 50%. In the absence of metabolic and carbon dioxide responses, the model predicts a constant level of blood flow that does not respond to changes in oxygen demand, suggesting the importance of these two response mechanisms. The model is not able to replicate the increase in oxygen venous saturation that has been observed in some flicker stimulation studies.
Conclusions: The increase in blood flow predicted by the model due to an increase in oxygen demand is not in the same proportion as the change in blood flow observed with the same decrease in oxygen demand, suggesting that vascular regulatory mechanisms may respond differently to different levels of oxygen demand. These results might be useful for interpreting clinical and experimental findings in health and disease.