Coupling blood flow and neural function in the retina: a model for homeostatic responses to ocular perfusion pressure challenge

Zheng He,Christine T O Nguyen,Jeremiah K H Lim,Algis J Vingrys,Bang V Bui

doi:10.1002/phy2.55

Zheng He, Christine T O Nguyen + Show 3 more

Open Access

https://doi.org/10.1002/phy2.55

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Journal: Physiological Reports	Publication Date: Aug 1, 2013
Citations: 50	License type: cc-by

Affiliation: University of Melbourne

Abstract

Retinal function is known to be more resistant than blood flow to acute reduction of ocular perfusion pressure (OPP). To understand the mechanisms underlying the disconnect between blood flow and neural function, a mathematical model is developed in this study, which proposes that increased oxygen extraction ratio compensates for relative ischemia to sustain retinal function. In addition, the model incorporates a term to account for a pressure-related mechanical stress on neurons when OPP reduction is achieved by intraocular pressure (IOP) elevation. We show that this model, combining ocular blood flow, oxygen extraction ratio, and IOP mechanical stress on neurons, accounts for retinal function over a wide range of OPP manipulations. The robustness of the model is tested against experimental data where ocular blood flow, oxygen tension, and retinal function were simultaneously measured during acute OPP manipulation. The model provides a basis for understanding the retinal hemodynamic responses to short-term OPP challenge.

Highlights

Ocular perfusion pressure (OPP) is the balance between mean arterial blood pressure (MAP) and intraocular pressure (IOP), that is, OPP = MAP À IOP
The internal consistency of the model was further demonstrated by showing similarities between theoretical and measured putative oxygen extraction ratio (OER, Fig. 6B) and IOP-mechanical stress (IOPM, Fig. 6C) components of OPP challenge
We showed that the decoupling between retinal function and ocular blood flow can be accounted for by the capacity of the eye to change oxygen extraction ratio and a nonvascular, pressure-related neuronal dysfunction

Summary

Introduction

During the acute OPP stress shown, there are compensatory mechanisms to maintain retinal blood flow and function to a certain extent An example of this is illustrated by the black circles in Figure 1 showing that when blood pressure is modified (at the normal IOP of 10 mmHg), blood flow does not change in a linear fashion, but shows a relative plateau at MAPs between 60 and 100 mmHg. An example of this is illustrated by the black circles in Figure 1 showing that when blood pressure is modified (at the normal IOP of 10 mmHg), blood flow does not change in a linear fashion, but shows a relative plateau at MAPs between 60 and 100 mmHg Outside this range, blood flow changes linearly with MAP.

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Conclusion