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      Role of the Dialyzer Membrane on the Overall Phosphate Kinetics during Hemodialysis

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          Background/Aim: We investigated the potential role of the membrane type on phosphate kinetics. Methods: Six patients on dialysis (HD) were studied using modified cellulose (Hemophan), ethylene-vinyl alcohol (EVAL) and polyacrylonitrile (PAN). Total (TPR), extracellular (EPR) and intracellular (IPR) phosphate removal and effective dialyzer phosphate clearance (K<sub>d</sub>) were determined by the DDQ method. The intercompartment transfer coefficient (K<sub>C</sub>) was calculated using a mathematical model. Erythrocyte phosphate (P<sub>ERY</sub>) and 2,3-biphosphoglycerate (2,3-BPG) concentrations were determined before and after HD. Results: TPR was 1.2 ± 0.4, 1.10 ± 0.4 and 1.09 ± 0.4 g with Hemophan, EVAL and PAN, respectively (p = n.s.). EPR and IPR were independent of membrane type. There was no difference in K<sub>C</sub> between membranes (321 ± 70, 338 ± 92 and 341 ± 83 ml/min, respectively). The P<sub>ERY</sub> and 2,3-BPG remained statistically insignificant for all membranes. Conclusion: Our results show that the type of membrane does not influence the kinetics of phosphate during dialysis, neither in the transfer from plasma to dialysate nor from the intra- to the extracellular compartment.

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          Most cited references 9

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          Protons and anaerobiosis.

          During oxygen limitation in animals, glucose can be fermented via several metabolic pathways varying in energetic efficiency and leading to various end products (such as lactate, alanopine, octopine, succinate, or propionate). Because of opposite pH dependencies of proton production by fermentation and by hydrolysis of adenosine triphosphate formed in the fermentation, the total number of moles of protons generated is always two per mole of the fermentable substrate. However, two and three times more adenosine triphosphate can be turned over per mole of protons produced in succinate and propionate fermentations, respectively, than in lactate fermentation.
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            Phosphate kinetics during hemodialysis: Evidence for biphasic regulation.

            Hyperphosphatemia in the hemodialysis population is ubiquitous, but phosphate kinetics during hemodialysis is poorly understood. Twenty-nine hemodialysis patients each received one long and one short dialysis, equivalent in terms of urea clearance. Phosphate concentrations were measured during each treatment and for one hour thereafter. A new model of phosphate kinetics was developed and implemented in VisSim. This model characterized additional processes involved in phosphate kinetics explaining the departure of the measured data from a standard two-pool model. Pre-dialysis phosphate concentrations were similar in long and short dialysis groups. Post-dialysis phosphate concentrations in long dialysis were higher than in short dialysis (P < 0.02) despite removal of a greater mass of phosphate (P < 0.001). In both long and short dialysis serum phosphate concentrations initially fell in accordance with two-pool kinetics, but thereafter plateaued or increased despite continuing phosphate removal. Implementation of an additional regulatory mechanism such that a third pool liberates phosphate to maintain an intrinsic target concentration (1.18 +/- 0.06 mmol/L; 95% confidence intervals, CI) explained the data in 24% of treatments. The further addition of a fourth pool hysteresis element triggered by critically low phosphate levels (0.80 +/- 0.07 mmol/L, CI) yielded an excellent correlation with the observed data in the remaining 76% of treatments (cumulative standard deviation 0.027 +/- 0.004 mmol/L, CI). The critically low concentration correlated with pre-dialysis phosphate levels (r=0.67, P < 0.0001). Modeling of phosphate kinetics during hemodialysis implies regulation involving up to four phosphate pools. The accuracy of this model suggests that the proposed mechanisms have physiological validity.
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                Author and article information

                Blood Purif
                Blood Purification
                S. Karger AG
                August 2005
                25 August 2005
                : 23
                : 5
                : 359-364
                aDepartment of Nephrology, University Hospital of Ioannina, and bDepartment of Clinical Health, Medical School, University of Ioannina, Ioannina, Greece
                87192 Blood Purif 2005;23:359–364
                © 2005 S. Karger AG, Basel

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                Page count
                Figures: 1, Tables: 5, References: 34, Pages: 6
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                Original Paper

                Cardiovascular Medicine, Nephrology

                Cellular clearance, Phosphate kinetics, Hemodialysis


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