scholarly journals Theoretical predictions of metabolic flow regulation in the retina

2016 ◽  
Vol 1 (2) ◽  
pp. 70-78
Author(s):  
Simone Cassani ◽  
Julia Arciero ◽  
Giovanna Guidoboni ◽  
Brent Siesky ◽  
Alon Harris
Keyword(s):  
Blood Flow ◽  
Oxygen Demand ◽  
Flow Regulation ◽  
Retinal Blood Flow ◽  
Regulatory Mechanisms ◽  
Tissue Oxygen ◽  
Theoretical Predictions ◽  
Health And Disease ◽  
Experimental Findings ◽  
Different Levels

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.

MODELLING HYDROGEN CLEARANCE FROM THE RETINA

2018 ◽  
Vol 59 (3) ◽  
pp. 281-292
Author(s):  
D. E. FARROW ◽  
G. C. HOCKING ◽  
S. J. CRINGLE ◽  
D.-Y. YU
Keyword(s):  
Blood Flow ◽  
Oxygen Supply ◽  
Retinal Blood Flow ◽  
Experimental Measurements ◽  
Human Retina ◽  
Light Path ◽  
Tissue Oxygen ◽  
Sophisticated Model ◽  
Tissue Oxygen Supply ◽  
Hydrogen Clearance

The human retina is supplied by two vascular systems: the highly vascular choroidal, situated behind the retina; and the retinal, which is dependent on the restriction that the light path must be minimally disrupted. Between these two circulations, the avascular retinal layers depend on diffusion of metabolites through the tissue. Oxygen supply to these layers may be threatened by diseases affecting microvasculature, for example diabetes and hypertension, which may ultimately cause loss of sight.An accurate model of retinal blood flow will therefore facilitate the study of retinal oxygen supply and, hence, the complications caused by systemic vascular disease. Here, two simple models of the blood flow and exchange of hydrogen with the retina are presented and compared qualitatively with data obtained from experimental measurements. The models capture some interesting features of the exchange and highlight effects that will need to be considered in a more sophisticated model and in the interpretation of experimental results.

Retinal Vascular Implications of Ocular Hypertension

2021 ◽  
Author(s):  
Fidan Jmor ◽  
John C. Chen
Keyword(s):  
Blood Flow ◽  
Diabetic Retinopathy ◽  
Intraocular Pressure ◽  
Vascular Anatomy ◽  
Flow Regulation ◽  
Retinal Blood Flow ◽  
Vein Occlusion ◽  
Ocular Perfusion ◽  
The Relationship ◽  
Central Retinal Vein

In this chapter, we review the basics of retinal vascular anatomy and discuss the physiologic process of retinal blood flow regulation. We then aim to explore the relationship between intraocular pressure and retinal circulation, taking into account factors that affect retinal hemodynamics. Specifically, we discuss the concepts of ocular perfusion pressure, baro-damage to the endothelium and transmural pressure in relation to the intraocular pressure. Finally, we demonstrate the inter-relationships of these factors and concepts in the pathogenesis of some retinal vascular conditions; more particularly, through examples of two common clinical pathologies of diabetic retinopathy and central retinal vein occlusion.

scholarly journals Interaction of the Nucleation Phenomena at Adjacent Sites in Nucleate Boiling

1983 ◽  
Vol 105 (1) ◽  
pp. 3-9 ◽  
Author(s):  
M. Sultan ◽  
R. L. Judd
Keyword(s):  
Active Sites ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Copper Surface ◽  
Nucleation Sites ◽  
Theoretical Predictions ◽  
Experimental Findings ◽  
Relationship Of ◽  
The Relationship ◽  
Different Levels

The present investigation is an original study in nucleate pool boiling heat transfer combining theory and experiment in which water boiling at atmospheric pressure on a single copper surface at two different levels of heat and different levels of subcooling was studied. Cross spectral analysis of the signals generated by the emission of bubbles at adjacent nucleation sites was used to determine the relationship of the time elapsed between the start of bubble growth at the two neighbouring active sites with the distance separating them. The experimental results obtained indicated that for the lower level of heat flux at three different levels of subcooling, the elapsed time and distance were directly related. Theoretical predictions of a temperature disturbance propagating through the heating surface in the radial direction gave good agreement with the experimental findings, suggesting that this is the mechanism responsible for the activation of the surrounding nucleation sites.

scholarly journals Theoretical Analysis of Vascular Regulatory Mechanisms Contributing to Retinal Blood Flow Autoregulation

2013 ◽  
Vol 54 (8) ◽  
pp. 5584 ◽  
Author(s):  
Julia Arciero ◽  
Alon Harris ◽  
Brent Siesky ◽  
Annahita Amireskandari ◽  
Victoria Gershuny ◽  
...  
Keyword(s):  
Blood Flow ◽  
Theoretical Analysis ◽  
Retinal Blood Flow ◽  
Regulatory Mechanisms

scholarly journals Functional Hyperemia and Mechanisms of Neurovascular Coupling in the Retinal Vasculature

2013 ◽  
Vol 33 (11) ◽  
pp. 1685-1695 ◽  
Author(s):  
Eric A Newman
Keyword(s):  
Blood Flow ◽  
Glial Cells ◽  
Neurovascular Coupling ◽  
Retinal Blood Flow ◽  
Retinal Vasculature ◽  
Functional Hyperemia ◽  
Cellular Mechanisms ◽  
Neuronal Stimulation ◽  
Health And Disease ◽  
Coupling Mechanisms

The retinal vasculature supplies cells of the inner and middle layers of the retina with oxygen and nutrients. Photic stimulation dilates retinal arterioles producing blood flow increases, a response termed functional hyperemia. Despite recent advances, the neurovascular coupling mechanisms mediating the functional hyperemia response in the retina remain unclear. In this review, the retinal functional hyperemia response is described, and the cellular mechanisms that may mediate the response are assessed. These neurovascular coupling mechanisms include neuronal stimulation of glial cells, leading to the release of vasoactive arachidonic acid metabolites onto blood vessels, release of potassium from glial cells onto vessels, and production and release of nitric oxide (NO), lactate, and adenosine from neurons and glia. The modulation of neurovascular coupling by oxygen and NO are described, and changes in functional hyperemia that occur with aging and in diabetic retinopathy, glaucoma, and other pathologies, are reviewed. Finally, outstanding questions concerning retinal blood flow in health and disease are discussed.

scholarly journals Retinal blood flow dysregulation precedes neural retinal dysfunction in type 2 diabetic mice

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Junya Hanaguri ◽  
Harumasa Yokota ◽  
Masahisa Watanabe ◽  
Satoru Yamagami ◽  
Akifumi Kushiyama ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Blood Flow ◽  
Flow Regulation ◽  
Laser Speckle ◽  
Retinal Blood Flow ◽  
Implicit Time ◽  
Laser Speckle Flowgraphy ◽  
Neural Function ◽  
Glucose Levels

AbstractWe investigated and compared the susceptibility of retinal blood flow regulation and neural function in mice developing type 2 diabetes. The longitudinal changes in retinal neuronal function and blood flow responses to a 10-min systemic hyperoxia and a 3-min flicker stimulation were evaluated every 2 weeks in diabetic db/db mice and nondiabetic controls (db/m) from age 8 to 20 weeks. The retinal blood flow and neural activity were assessed using laser speckle flowgraphy and electroretinography (ERG), respectively. The db/db mice had significantly higher blood glucose levels and body weight. The resting retinal blood flow was steady and comparable between two groups throughout the study. Hyperoxia elicited a consistent decrease, and flicker light an increase, in retinal blood flow in db/m mice independent of age. However, these flow responses were significantly diminished in db/db mice at 8 weeks old and then the mice became unresponsive to stimulations at 12 weeks. Subsequently, the ERG implicit time for oscillatory potential was significantly increased at 14 weeks of age while the a-wave and b-wave amplitudes and implicit times remained unchanged. The deficiencies of flow regulation and neurovascular coupling in the retina appear to precede neural dysfunction in the mouse with type 2 diabetes.

Role of Nitric Oxide in Mediating Retinal Blood Flow Regulation in Cats

1999 ◽  
Vol 15 (4) ◽  
pp. 295-303 ◽  
Author(s):  
SEIYO HARINO ◽  
KAZUO NISHIMURA ◽  
KUNIKO KITANISHI ◽  
MINA SUZUKI ◽  
PETER REINACH
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Flow Regulation ◽  
Retinal Blood Flow ◽  
Blood Flow Regulation

scholarly journals Overview of mathematical modeling of myocardial blood flow regulation

2020 ◽  
Vol 318 (4) ◽  
pp. H966-H975
Author(s):  
Ravi Namani ◽  
Yoram Lanir ◽  
Lik Chuan Lee ◽  
Ghassan S. Kassab
Keyword(s):  
Blood Flow ◽  
Coronary Blood Flow ◽  
Coronary Flow ◽  
Oxygen Demand ◽  
Flow Regulation ◽  
Flow Reserve ◽  
Arterial Blood ◽  
Blood Flow Regulation ◽  
Highly Nonlinear ◽  
Coronary Flow Regulation

The oxygen consumption by the heart and its extraction from the coronary arterial blood are the highest among all organs. Any increase in oxygen demand due to a change in heart metabolic activity requires an increase in coronary blood flow. This functional requirement of adjustment of coronary blood flow is mediated by coronary flow regulation to meet the oxygen demand without any discomfort, even under strenuous exercise conditions. The goal of this article is to provide an overview of the theoretical and computational models of coronary flow regulation and to reveal insights into the functioning of a complex physiological system that affects the perfusion requirements of the myocardium. Models for three major control mechanisms of myogenic, flow, and metabolic control are presented. These explain how the flow regulation mechanisms operating over multiple spatial scales from the precapillaries to the large coronary arteries yield the myocardial perfusion characteristics of flow reserve, autoregulation, flow dispersion, and self-similarity. The review not only introduces concepts of coronary blood flow regulation but also presents state-of-the-art advances and their potential to impact the assessment of coronary microvascular dysfunction (CMD), cardiac-coronary coupling in metabolic diseases, and therapies for angina and heart failure. Experimentalists and modelers not trained in these models will have exposure through this review such that the nonintuitive and highly nonlinear behavior of coronary physiology can be understood from a different perspective. This survey highlights knowledge gaps, key challenges, future research directions, and novel paradigms in the modeling of coronary flow regulation.

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