Should the Lopot-Plot Be Used in Daily Practice to Optimise Hemodialysis Treatment?

2012 ◽  
Vol 8 (4) ◽  
pp. 417-423
Author(s):  
Przemysław Korohoda ◽  
Przemysław Sypka ◽  
Jacek A. Pietrzyk
Keyword(s):  
Steady State ◽  
Planning Process ◽  
Computational Study ◽  
Daily Practice ◽  
Urea Concentration ◽  
Hemodialysis Treatment

ABSTRACT The paper presents an application of the Lopot-plot, which compares the timeaveraged concentration (TAC) and the time-averaged deviation (TAD) of the weekly dialysis cycle, to comprise the results of intensive computational study. The presented case is based on 420 one-week-cycle simulations to verify the consequences implied by the change of the treatments schedule from nonuniformly to uniformly distributed over the week. The concept of steady state is explained and utilized to obtain periodical runs of the urea concentration. The presented graphs encouragingly indicate the potential of such plots in presenting results of multivariable intensive computations that should be advisably performed during the planning process of hemodialysis treatment.

Restitution and adaptation measurements for the estimate of short-term cardiac action potential memory: comparison of five human ventricular models

EP Europace ◽  
2019 ◽  
Vol 21 (10) ◽  
pp. 1594-1602
Author(s):  
Massimiliano Zaniboni ◽  
Francesca Cacciani
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Short Term Memory ◽  
Computational Study ◽  
Numerical Models ◽  
Cardiac Action Potential ◽  
Short Term ◽  
Term Memory ◽  
Cardiac Action

Abstract Aims This computational study refines our recently published pacing protocol to measure short-term memory (STM) of cardiac action potential (AP), and apply it to five numerical models of human ventricular AP. Methods and results Several formulations of electrical restitution (ER) have been provided over the years, including standard, beat-to-beat, dynamic, steady-state, which make it difficult to compare results from different studies. We discuss here the notion of dynamic ER (dER) by relating it to its steady-state counterpart, and propose a pacing protocol based on dER to measure STM under periodically varying pacing cycle length (CL). Under high and highly variable-pacing rate, all models develop STM, which can be measured over the entire sequence by means of dER. Short-term memory can also be measured on a beat-to-beat basis by estimating action potential duration (APD) adaptation after clamping CL constant. We visualize STM as a phase shift between action potential (AP) parameters over consecutive cycles of CL oscillations, and show that delay between CL and APD oscillation is nearly constant (around 92 ms) in the five models, despite variability in their intrinsic AP properties. Conclusion dER, as we define it and together with other approaches described in the study, provides an univocal way to measure STM under extreme cardiac pacing conditions. Given the relevance of AP memory for repolarization dynamics and stability, STM should be considered, among other usual biomarkers, to validate and tune cardiac AP models. The possibility of extending the method to in vivo cellular and whole organ models can also be profitably explored.

The Peak Concentration Hypothesis: A Urea Kinetic Approach to Comparing the Adequacy of Continuous Ambulatory Peritoneal Dialysis (CAPD) and Hemodialysis

1989 ◽  
Vol 9 (4) ◽  
pp. 257-260 ◽  
Author(s):  
Prakash R. Keshaviah ◽  
Karl D. Nolph ◽  
John C. Van Stone
Keyword(s):  
Peritoneal Dialysis ◽  
Steady State ◽  
Continuous Ambulatory Peritoneal Dialysis ◽  
Protein Intake ◽  
Peak Concentration ◽  
Treatment Time ◽  
Urea Concentration ◽  
Intermittent Therapy ◽  
The Hours ◽  
National Cooperative

The KTIV urea index ( K, clearance; T, treatment time; V, volume of urea distribution) has become an established index of hemodialysis (HD) adequacy, values of KTIV < 0.8 being associated with overt uremic toxicity. For the typical continuous ambulatory peritoneal dialysis (CAPD) regimen of 4 X 2 L exchanges/day, the equivalent KT/V -0.6. Paradoxically, overt uremic toxicity is not commonly observed in CAPD patients with this typical therapy prescription. Application of the urea kinetic model demonstrates that HD and CAPD have the same time-averaged urea concentration at the same KTIV. However, as HD is an intermittent therapy, the urea concentration in HD exceeds the time-averaged concentration for about half the hours in the week. If uremic toxicity is related to the peak rather than the time-averaged urea concentration, a higher KT/V would be required in HD to achieve a peak concentration at or below the steady state CAPD concentration. This peak concent ration hypothesis predicts, based on the results of the National Cooperative Dialysis Study, that underdialysis with CAPD would occur at KT/V < 0.4 for a protein intake of 1.1 gmlkglday.

scholarly journals Ménage à Trois: The Role of Neurotransmitters in the Energy Metabolism of Astrocytes, Glutamatergic, and GABAergic Neurons

2012 ◽  
Vol 32 (8) ◽  
pp. 1472-1483 ◽  
Author(s):  
Daniela Calvetti ◽  
Erkki Somersalo
Keyword(s):  
Steady State ◽  
Computational Study ◽  
Quantitative Description ◽  
Gaba Release ◽  
Cell Types ◽  
High Rate ◽  
Arterial Blood Flow ◽  
Gamma Aminobutyric Acid ◽  
Arterial Blood ◽  
Glucose Partitioning

This work is a computational study based on a new detailed metabolic network model comprising well-mixed compartments representing separate cytosol and mitochondria of astrocytes, glutamatergic and gamma aminobutyric acid (GABA)ergic neurons, communicating through an extracellular space compartment and fed by arterial blood flow. Our steady-state analysis assumes statistical mass balance of both carbons and amino groups. The study is based on Bayesian flux balance analysis, which uses Markov chain Monte Carlo sampling techniques and provides a quantitative description of steady states when the two exchangers aspartate-glutamate carrier (AGC1) and oxoglutarate carrier (OGC) in the malate-aspartate shuttle in astrocyte are not in equilibrium, as recent studies suggest. It also highlights the importance of anaplerotic reactions, pyruvate carboxylase in astrocyte and malic enzyme in neurons, for neurotransmitter synthesis and recycling. The model is unbiased with respect to the glucose partitioning between cell types, and shows that determining the partitioning cannot be done by stoichiometric constraints alone. Furthermore, the intercellular lactate trafficking is found to depend directly on glucose partitioning, suggesting that a steady state may support different scenarios. At inhibitory steady state, characterized by high rate of GABA release, there is elevated oxidative activity in astrocyte, not in response to specific energetic needs.

Mild Steady-State Exercise During Hemodialysis Treatment

1984 ◽  
Vol 12 (6) ◽  
pp. 153-157 ◽  
Author(s):  
Edmund J. Burke ◽  
Michael J. Germain ◽  
Gregory L. Braden ◽  
John P. Fitzgibbons
Keyword(s):  
Steady State ◽  
Hemodialysis Treatment

A combined kinetic and computational study of the reactions of transient germylenes with oxiranes and thiiranes in solution

2015 ◽  
Vol 93 (4) ◽  
pp. 435-444 ◽  
Author(s):  
Svetlana S. Kostina ◽  
William J. Leigh
Keyword(s):  
Steady State ◽  
Lewis Acid ◽  
Density Functional ◽  
Computational Study ◽  
Equilibrium Constants ◽  
Density Functional Theory Calculations ◽  
Laser Flash ◽  
Acid Base ◽  
Hydrocarbon Solvents ◽  
Complexation Reactions

The reactions of dimethyl- and diphenylgermylene (GeMe2 and GePh2, respectively) with cyclohexene oxide (CHO) and propylene sulfide (PrS) have been studied in hydrocarbon solvents at 25 °C by laser flash and steady-state photolysis methods using appropriately substituted germacyclopent-3-ene derivatives as germylene precursors. GeMe2 reacts with CHO and PrS with rate constants in the range of 1.2–1.7 × 1010 M−1 s−1 in hexanes at 25 °C to form new transient products that are assigned to the corresponding Lewis acid-base complexes of the germylene with the substrates. The complexation reactions were found to be reversible and are characterized by equilibrium constants of KC = (3.7 ± 0.8) × 103 M−1 and (3 ± 1) × 104 M−1 for complexation of GeMe2 with CHO and PrS, respectively. The complexes decay over approximately 10 μs with the concomitant formation of tetramethyldigermene (Ge2Me4), identifiable by its characteristic UV-vis spectrum centered at λmax = 370 nm. Diphenylgermylene behaves analogously, reacting rapidly and reversibly with the two substrates to form the corresponding Lewis acid-base complexes (λmax ≈ 355 nm) that decay over several tens of microseconds with the concomitant growth of the characteristic UV-vis spectrum of tetraphenyldigermene (Ge2Ph4) (λmax = 440 nm). Steady-state photolysis of the germylene precursors in the presence of CHO afforded germanium-containing oligomers but showed no evidence of oxygen abstraction or the formation of substrate-derived product(s). Similar photolyses in the presence of PrS also afforded germanium-containing oligomers, but as well yielded propene in 20%–30% yield and (in the case of the GePh2 precursor) minor amounts of low molecular weight compounds that appear to be derived from the corresponding germanethione. Density functional theory calculations of the chalcogen abstraction reactions of GeMe2 with oxirane and thiirane in the gas phase have been carried out at the B3LYP/6-311+G(d,p) level of theory and are in good qualitative agreement with the experimental data.

Effects of urea on the in vitro production of prostaglandins and on urinary excretion in Brattleboro rats

1989 ◽  
Vol 120 (4) ◽  
pp. 459-465 ◽  
Author(s):  
Eigil Bojesen ◽  
Inge N. Bojesen
Keyword(s):  
Steady State ◽  
Urinary Excretion ◽  
Urea Concentration ◽  
Brattleboro Rats ◽  
Sprague Dawley ◽  
Sprague Dawley Rats ◽  
Urine Formation ◽  
Excretion Rates

Abstract. Brattleboro rats with hereditary diabetes insipidus make it possible to investigate effects of the urea concentration on the in vitro and in vivo production of prostaglandins E2 and F2α (PGE2 and PGF2α) by the renal papilla independently of any vasopressin effects. The rates of prostaglandin production in vitro are increasing between 100 and 1030 mmol/l urea and decreasing above 1030 mmol/l. The ratio PGE2/PGF2α remains constant at about 4. Normally hydrated and 24 h water-deprived animals in steady state of urine formation were compared in vivo. Urine osmolality increased from 167 ± 6 (N = 5) to 1113 ± 35 (N = 15) mosmol/kg water and papillary urea concentration from 50 ± 7 to 304 ± 19 mmol/l after water deprivation. Urinary excretion rates of PGF2α increased from 0.83 ± 0.12 to 3.80 ± 0.37 ng/h. The excretion of PGE2 was unaffected. PGE2 + PGF2α excretion rates increased from 1.62 ± 0.25 to 4.61 ± 0.42 ng/h. These values are in accordance with values predicted from work with Sprague-Dawley rats. Together with previously published data on Sprague-Dawley rats these results indicate that variations of prostaglandin production in the conscious rat in steady state of urine formation can be accounted for by variations of plasma vasopressin and of papillary urea concentration. Variations in the excretion fraction are due to other causes.

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