The opto-respiratory compromise: Balancing oxygen supply and light transmittance in the retina

Physiology ◽  
2021 ◽  
Author(s):  
Christian Damsgaard ◽  
Michael William Country
Keyword(s):  
Blood Vessels ◽  
Oxygen Supply ◽  
Oxygen Demand ◽  
Blood Perfusion ◽  
High Oxygen ◽  
Light Transmittance ◽  
Light Path ◽  
Respiratory Compromise ◽  
High Oxygen Demand ◽  
Physiological Systems

The light-absorbing retina has an exceptionally high oxygen demand, which imposes two conflicting needs: high rates of blood perfusion and an unobstructed light path devoid of blood vessels. This review discusses mechanisms and physiological tradeoffs underlying retinal oxygen supply in vertebrates and examines how these physiological systems supported the evolution of vision.

A case of unusually high oxygen demand in a eutrophic lake

Hydrobiologia ◽  
1991 ◽  
Vol 209 (3) ◽  
pp. 235-243 ◽  
Author(s):  
Harjeet S. Sehgal ◽  
Eugene B. Welch
Keyword(s):  
Oxygen Demand ◽  
Eutrophic Lake ◽  
High Oxygen ◽  
High Oxygen Demand

scholarly journals Hypoferremia predicts hospitalization and oxygen demand in COVID-19 patients

2020 ◽  
Author(s):  
Theresa Hippchen ◽  
Sandro Altamura ◽  
Martina U. Muckenthaler ◽  
Uta Merle
Keyword(s):  
Iron Metabolism ◽  
Serum Iron ◽  
Iron Concentration ◽  
Oxygen Demand ◽  
Multivariate Regression Analysis ◽  
High Oxygen ◽  
University Hospital ◽  
List Type ◽  
Inflammatory Parameters ◽  
High Oxygen Demand

ABSTRACTBackgroundIron metabolism might play a crucial role in cytokine release syndrome in COVID-19 patients. Therefore we assessed iron metabolism markers in COVID-19 patients for their ability to predict disease severity.MethodsCOVID-19 patients referred to the Heidelberg University Hospital were retrospectively analyzed. Patients were divided into outpatients (cohort A, n=204), inpatients (cohort B, n=81), and outpatients later admitted to hospital because of health deterioration (cohort C, n=23).ResultsIron metabolism parameters were severely altered in patients of cohort B and C compared to cohort A. In multivariate regression analysis including age, gender, CRP and iron-related parameters only serum iron and ferritin were significantly associated with hospitalization. ROC analysis revealed an AUC for serum iron of 0.894 and an iron concentration <6µmol/l as the best cutoff-point predicting hospitalization with a sensitivity of 94.7% and a specificity of 67.9%. When stratifying inpatients in a low- and high oxygen demand group serum iron levels differed significantly between these two groups and showed a high negative correlation with the inflammatory parameters IL-6, procalcitonin, and CRP. Unexpectedly, serum iron levels poorly correlate with hepcidin.ConclusionWe conclude that measurement of serum iron can help predicting the severity of COVID-19. The differences in serum iron availability observed between the low and high oxygen demand group suggest that disturbed iron metabolism likely plays a causal role in the pathophysiology leading to lung injury.KEY POINTSIron metabolism parameters are severely altered in COVID-19 patients.Measurement of serum iron can help predicting the severity of COVID-19.

Perfusion-independent oxygen extraction in myoglobin-rich hearts

1988 ◽  
Vol 135 (1) ◽  
pp. 301-315
Author(s):  
J. R. Bailey ◽  
W. R. Driedzic
Keyword(s):  
Oxygen Consumption ◽  
Flow Rate ◽  
Oxygen Demand ◽  
High Oxygen ◽  
Oxygen Extraction ◽  
Oxidizing Agent ◽  
Flow Rates ◽  
Sea Raven ◽  
High Oxygen Demand

Cardiac myoglobin plays a role in oxygen consumption and has a protective effect during periods of hypoxia, but little is known about the role of myoglobin during periods of ischaemia. Myoglobin-rich sea raven hearts and myoglobin-poor ocean pout hearts were isolated and perfused at varying flow rates and under conditions of low and high oxygen demand to assess the role of myoglobin in oxygen extraction. In the myoglobin-rich hearts, oxygen extraction remained constant over the flow range. In the myoglobin-poor hearts, oxygen extraction was significantly elevated, relative to controls, at the lower flow rates but decreased as the flow rate increased. In hearts where myoglobin was inactivated by an oxidizing agent, oxygen extraction was similar to that observed in myoglobin-poor hearts. Under conditions of high oxygen demand, myoglobin-rich hearts again showed a constant oxygen extraction over the flow range. Myoglobin-inactivated hearts had a significantly elevated oxygen extraction at low flows, and this decreased as flow rate increased. These data suggest that myoglobin renders oxygen extraction by fish hearts independent of the rate of perfusion.

Use of Naso-Tracheal Oxygen Catheter During Bronchoscopy in Patients With High Oxygen Demand

CHEST Journal ◽  
2013 ◽  
Vol 144 (4) ◽  
pp. 802A
Author(s):  
Justin Thomas ◽  
Michael Galloway ◽  
Ali Musani
Keyword(s):  
Oxygen Demand ◽  
High Oxygen ◽  
High Oxygen Demand

A high oxygen demand in normal tension glaucoma

2015 ◽  
Vol 93 ◽  
pp. n/a-n/a
Author(s):  
C. Turksever ◽  
M. Todorova ◽  
S. Orguel
Keyword(s):  
Oxygen Demand ◽  
Normal Tension Glaucoma ◽  
High Oxygen ◽  
High Oxygen Demand

Comparison of mayfly (Ephemeroptera) taxocenes of permanent and intermittent Central European small streams via species traits

Biologia ◽  
2010 ◽  
Vol 65 (4) ◽  
Author(s):  
Pavla Řezníčková ◽  
Tomáš Soldán ◽  
Petr Pařil ◽  
Světlana Zahrádková
Keyword(s):  
Global Climate ◽  
Extreme Temperature ◽  
Oxygen Demand ◽  
Hydrological Regime ◽  
Species Traits ◽  
Individual Species ◽  
Biological Traits ◽  
Small Streams ◽  
High Oxygen Demand ◽  
The Impact

AbstractThe recurrent drying out of small streams in past decades has shown an urgent need to pay attention to the impact of global climate change. The objectives of this study were to describe the effect of drying out on the composition of the mayfly taxocene and evaluate the relevance of individual species traits for survival of mayflies to drying out. The mayfly taxocenes of two model localities, one at an intermittent and one at a permanent brook, were investigated in 2002, 2003 and 2005. Compared with the permanent stream, the taxocene of the intermittent stream was short of nine species, foremost rheobionts and high oxygen demand species. To explain further differences between both stream types in survival and recolonisation ability, 15 species traits were evaluated. These included so-called “ecological traits” (e.g., habitat and substrate range, density, distribution, current velocity adaptation) and “biological traits” connected with life cycle and larval/adult adaptations. Species showing the highest number of advantageous traits (with only exception of Electrogena sp. cf. ujhelyii — species of taxonomically unclear status) were able to successfully survive under the unfavourable conditions of the intermittent brook. Biological traits considered more important in many respects seem to be good predictors for assessing sensitivity to extreme temperature changes, hydrological regime fluctuations and the survival/recolonisation ability of species in exposed habitats.

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.

d-Propranolol prevents adenosine formation associated with myocardial hypoperfusion

1989 ◽  
Vol 256 (3) ◽  
pp. H772-H778 ◽  
Author(s):  
R. D. Wangler ◽  
W. P. Peterson ◽  
H. V. Sparks
Keyword(s):  
Coronary Flow ◽  
Oxygen Supply ◽  
Perfusion Pressure ◽  
Oxygen Demand ◽  
Myocardial Tissue ◽  
Adenosine Release ◽  
Consumption Ratio ◽  
Similar Decrease ◽  
Myocardial Hypoperfusion ◽  
Vascular Compartment

d-Propranolol eliminates the increased adenine nucleoside release from hypoperfused hearts [R. D. Wangler, D. F. DeWitt, and H. V. Sparks, Am. J. Physiol. 247 (Heart Circ. Physiol. 16): H330-H336, 1984]. To determine whether d-propranolol reduces adenosine formation or adenosine release into the vascular compartment, we measured myocardial tissue adenosine (TADO). Decreased formation would lower TADO, whereas decreased release would elevate TADO. Reduction of perfusion pressure by 50% reduced coronary flow (CF), venous oxygen tension (PVO2), and myocardial oxygen consumption (MVO2) by approximately 40, 25, and 35%, respectively. Total adenosine and inosine released during 30 min of hypoperfusion increased 10- and 5-fold, respectively. Also, TADO increased from 2.68 +/- 0.37 to 5.17 +/- 0.67 nmol/g (P less than 0.05). In the presence of d-propranolol, the same reduction in perfusion pressure caused a similar decrease in CF and MVO2. d-Propranolol eliminated the release of adenosine and inosine associated with hypoperfusion. TADO after 30 min of hypoperfusion plus d-propranolol was not significantly increased (3.27 +/- 0.40 nmol/g) and was significantly less than hypoperfused hearts. When severe hypoperfusion was created by reducing perfusion pressure 75%, adenosine release still did not increase if d-propranolol was present. When adenosine release was plotted as a function of oxygen supply-consumption, they were related in a hyperbolic fashion. Despite the severity of hypoperfusion, in the presence of d-propranolol the supply-to-consumption ratio was similar to that of the control perfusion group (no drug). We conclude that d-propranolol blocks nucleoside formation during hypoperfusion by reducing oxygen demand such that a reduction of oxygen supply no longer stimulates adenosine formation.

Oxygen partial pressure and free intracellular adenosine of isolated cardiomyocytes

1991 ◽  
Vol 260 (4) ◽  
pp. C708-C714 ◽  
Author(s):  
R. T. Smolenski ◽  
J. Schrader ◽  
H. de Groot ◽  
A. Deussen
Keyword(s):  
Oxygen Consumption ◽  
Extracellular Space ◽  
Oxygen Supply ◽  
Oxygen Demand ◽  
Nucleoside Transport ◽  
Isolated Cardiomyocytes ◽  
Homocysteine Thiolactone ◽  
Rat Cardiomyocytes ◽  
Extracellular Adenosine ◽  
Adenosine Concentration

Adenosine formation by the heart is known to critically depend on the ratio of oxygen supply to oxygen demand, but the sensitivity of cardiomyocytes to defined changes in PO2 is not known. Isolated metabolically stable rat cardiomyocytes were incubated up to 45 min at constant PO2 values ranging from 0.1 to 100 mmHg using a feedback-controlled incubation system (oxystat system). Changes of the free intracellular adenosine concentration were measured after trapping of adenosine by cytosolic S-adenosylhomocysteine (SAH) hydrolase in the presence of 200 microM L-homocysteine thiolactone. Rate of SAH formation was constant at a PO2 between 3 and 100 mmHg and gradually increased at PO2 less than 3 mmHg. Cellular ATP decreased only at PO2 less than 1 mmHg, and this was accompanied by a decline of oxygen consumption. Treatment of cells with 5.5 mM deoxyglucose and 4 micrograms/ml oligomycin increased SAH formation 60-fold and was associated with elevated intra- and to a lesser extent extracellular adenosine levels. Inhibition of nucleoside transport with 20 microM S-(p-nitrobenzyl)-6-thioinosine steepened the transmembrane adenosine gradient. Our findings suggest that the cardiomyocyte responds to metabolic poisoning and oxygen deprivation with an enhanced formation of adenosine. This adenosine is mainly formed intracellularly and reaches the extracellular space by diffusion. Threshold for adenosine formation is as low as 3 mmHg.

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