Biomedical subjects

Sunny Eloot

Publications and source records attributed to Sunny Eloot.

7 recordsLinked to original sources

PubMed2006

Three-dimensional numerical modeling and computational fluid dynamics simulations to analyze and improve oxygen availability in the AMC bioartificial liver.

A numerical model to investigate fluid flow and oxygen (O(2)) transport and consumption in the AMC-Bioartificial Liver (AMC-BAL) was developed and applied to two representative micro models of the AMC-BAL with two different gas capillary patterns, each combined with two proposed hepatocyte distributions. Parameter studies were performed on each configuration to gain insight in fluid flow, shear stress distribution and oxygen availability in the AMC-BAL. We assessed the function of the internal oxygenator, the effect of changes in hepatocyte oxygen consumption parameters in time and the effect of the change from an experimental to a clinical setting. In addition, different methodologies were studied to improve cellular oxygen availability, i.e. external oxygenation of culture medium, culture medium flow rate, culture gas oxygen content (pO(2)) and the number of oxygenation capillaries. Standard operating conditions did not adequately provide all hepatocytes in the AMC-BAL with sufficient oxygen to maintain O(2) consumption at minimally 90% of maximal uptake rate. Cellular oxygen availability was optimized by increasing the number of gas capillaries and pO(2) of the oxygenation gas by a factor two. Pressure drop over the AMC-BAL and maximal shear stresses were low and not considered to be harmful. This information can be used to increase cellular efficiency and may ultimately lead to a more productive AMC-BAL.

Cell Culture Techniques↗

PubMed2006

Clamping of the dialysate outlet line in the Genius dialysis system does not alter dialysate flow or clearances.

BACKGROUND: The Genius dialysis system is advocated as a tool to perform slow extended daily dialysis (SLEDD) in patients with acute renal failure at the intensive care unit. At low blood flows however, it is sometimes problematic to maintain sufficient systemic pressure in the dialysate circuit, a problem that can be overcome by clamping the dialysate outflow line. This intervention can however decrease the flow in the dialysate circuit, and can thus potentially decrease the clearance. This article analyses the impact of this intervention on the blood and dialysate flows and on the removal of retention products. METHODS: The study was done in 20 stable chronic dialysis patients to avoid additional bias caused by changing comorbidities in ICU patients. Patients were treated by Genius, once with clamping and once without clamping, cross-over in a randomized fashion, and with 1 week interval. Flows in the dialysate and blood circuit were measured with a transsonic flow probe. Urea, creatinine, Beta 2 microglobulin and phosphate were measured in the dialysate, and in the serum before and after dialysis. RESULTS: There was no clinically significant difference in blood or dialysate flows, nor in clearance or removal of retention products during the sessions with or without clamping. CONCLUSIONS: The technique of using clamping of the dialysate outflow line in the Genius system to increase systemic pressure, when the system is used in SLEDD, is a safe technique which does not alter the clearances.

Aged↗

PubMed2005

Efficiency of the Genius batch hemodialysis system with low serum solute concentrations: the case of lithium intoxication therapy.

BACKGROUND: The Genius batch system consists of a 90-L closed reservoir, from which fresh dialysate is extracted at the top and to which spent dialysate is returned at the bottom. It was shown in long-term hemodialysis patients that almost the entire amount of unspent dialysate can be used before contamination of fresh with spent dialysate occurs. Separation is caused by differences in density, partly because of the presence of uremic solutes in spent dialysate. The question is raised whether this separation can be maintained during dialysis of patients who experience an intoxication without renal failure. METHODS: A patient intoxicated with lithium was dialyzed using the Genius system, prepared at 37 degrees C, during 300 minutes. With dialysate flow set at 300 mL/min (5 mL/s) and in the absence of mixing, urea is not expected at the inlet dialysate tubing before minute 300. RESULTS: In the dialysate inlet tubing, an abrupt increase in lithium and urea concentrations was observed 210 minutes after the start of the session, reflecting contamination of fresh with spent dialysate. At minute 210, only 60.9 L of 90 L of dialysate had crossed the dialyzer. In a control dialysis treatment in a patient with marked renal failure, this mixing occurred only at 300 minutes. CONCLUSION: In the present observation, it is shown that during Genius dialysis in a patient without renal failure, an earlier contamination of fresh with spent dialysate can occur, compared to conditions of renal failure.

Adult↗

PubMed2005

Middle molecule removal in low-flux polysulfone dialyzers: impact of flows and surface area on whole-body and dialyzer clearances.

Some studies found that the removal of middle molecules has a long-term effect on mortality and, even more, is enhanced by high-flux dialysis. In order to enhance middle molecule removal in a low-flux dialyzer, the present study aimed at investigating the combined impact of dialyzer flows and membrane surface area. Blood and dialysate flows were varied within the clinical range 300-500 and 500-800 mL/min, respectively, while the ultrafiltration rate was kept constant at 0.1 L/hr. Single-pass tests were performed in vitro in a single Fresenius F6HPS dialyzer (3 tests) and serially (5 tests) and parallel (3 tests) connected dialyzers. The blood substitution fluid consisted of dialysis fluid in which radioactive-labeled vitamin B12 (molecular weight 1355 Da) was dissolved. Dialyzer clearance as well as whole-body clearance was calculated from radioactivity concentrations of samples taken from the inlet and outlet bloodline. Adding a second dialyzer in series or parallel ameliorated the overall dialyzer and whole-body clearance significantly, except for the highest applied blood flows of 500 mL/min. Better solute removal was also obtained with higher dialysate flows, while the use of higher blood flows seemed advantageous only when using a single dialyzer. Analysis of the ultrafiltration profiles in the different configurations illustrated that enhancing the internal filtration rate ameliorates convective transport of middle molecules. Adequate solute removal results from a number of interactions, as there are blood and dialysate flows, membrane surface area, filtration profile and concentration profiles in the blood and dialysate compartment.

Hemodialysis Solutions↗

PubMed2005

Kinetic behavior of urea is different from that of other water-soluble compounds: the case of the guanidino compounds.

BACKGROUND: Although patients with renal failure retain a large variety of solutes, urea is virtually the only currently applied marker for adequacy of dialysis. Only a limited number of other compounds have up until now been investigated regarding their intradialytic kinetics. Scant data suggest that large solutes show a kinetic behavior that is different from urea. The question investigated in this study was whether other small water-soluble solutes, such as some guanidino compounds, show a kinetic behavior comparable or dissimilar to that of urea. METHODS: This study included 7 stable conventional hemodialysis patients without native kidney function undergoing low flux polysulphone dialysis (F8 and F10HPS). Blood samples were collected from the inlet and outlet bloodlines immediately before the dialysis session, after 5, 15, 30, 120 minutes, and immediately after discontinuation of the session. Plasma concentrations of urea, creatinine (CTN), creatine (CT), guanidinosuccinic acid (GSA), guanidinoacetic acid (GAA), guanidine (G), and methylguanidine (MG) were used to calculate corresponding dialyzer clearances. A two-pool kinetic model was fitted to the measured plasma concentration profiles, resulting in the calculation of the perfused volume (V(1)), the total distribution volume (V(tot)), and the intercompartmental clearance (K(12)); solute generation and overall ultrafiltration were determined independently. RESULTS: No significant differences were observed between V(1) and K(12) for urea (6.4 +/- 3.3 L and 822 +/- 345 mL/min, respectively) and for the guanidino compounds. However, with respect to V(tot), GSA was distributed in a smaller volume (30.6 +/- 4.2 L) compared to urea (42.7 +/- 6.0L) (P < 0.001), while CTN, CT, GAA, G, and MG showed significantly higher volumes (54.0 +/- 5.9 L, 98.0 +/- 52.3 L, 123.8 +/- 66.9 L, 89.7 +/- 21.4 L, 102.6 +/- 33.9 L, respectively; P= 0.004, = 0.033, = 0.003, < 0.001, = 0.001, respectively). These differences resulted in divergent effective solute removal: 67% (urea), 58% (CTN), 42% (CT), 76% (GSA), 37% (GAA), 43% (G), and 42% (MG). CONCLUSION: The kinetics of the guanidino compounds under study are different from that of urea; hence, urea kinetics are not representative for the removal of other uremic solutes, even if they are small and water-soluble like urea.

Aged↗

PubMed2005

Dialysate partitioning in the Genius batch hemodialysis system: effect of temperature and solute concentration.

BACKGROUND: The Genius batch system contains a 75-L closed reservoir from which fresh dialysate is extracted at the top, and to which spent dialysate is returned at the bottom. In vivo studies have demonstrated that almost the entire amount of dialysate can be used before contamination of fresh with spent dialysate occurs. The question is raised whether density differences cause this separation, and what the relative contributions of temperature and solute content are. METHODS: As patient substitute, a container filled with dialysate was loaded with various amounts of urea. Temperature differences between spent and fresh dialysate were imposed by not heating the dialysate at the outlet line from the dialyzer (A), heating the outlet to obtain continuously equal temperatures at inlet and outlet (B), or to temperatures as in vivo (C). With a dialysate flow set at 300 mL/min, urea is not expected at the inlet before 250 minutes. RESULTS: With a urea concentration of 33 mg/dL, urea contamination at the dialysate inlet line occurred after 185 +/- 20 (A), 122 +/- 11 (B), and 175 +/- 12 minutes (C) of dialysis, whereas with 67 mg/dL, this happened at 219 +/- 5 (A), 162 +/- 11 (B), and 202 +/- 8 minutes (C). With 100 and 150 mg/dL, urea contamination appeared at 224 +/- 2 (A) and 204 +/- 14 minutes (B), and 227 +/- 5 (A) and 232 +/- 3 minutes (B), respectively. CONCLUSION: Both temperature differences between spent and fresh dialysate and solute content of spent dialysate contribute to dialysate partitioning in the Genius dialysis system.

Dialysis Solutions↗

PubMed2002

Computational flow modeling in hollow-fiber dialyzers.

A three-dimensional finite volume model of the blood-dialysate interface over the complete length of the dialyzer was developed. Different equations govern dialyzer flow and pressure distribution (Navier-Stokes) and radial transport (Darcy). Blood was modeled as a non-Newtonian fluid with a viscosity varying in radial and axial direction determined by the local hematocrit, the diameter of the capillaries, and the local shear rate. The dialysate flow was assumed to be an incompressible, isothermal laminar Newtonian flow with a constant viscosity. The permeability characteristics of the membrane were calculated from laboratory tests for forward and backfiltration. The oncotic pressure induced by the plasma proteins was implemented as well as the reduction of the overall permeability caused by the adhesion of proteins to the membrane. From the calculated pressure distribution, the impact of flow, hematocrit, and capillary dimensions on the presence and localization of backfiltration can be investigated.

Blood Flow Velocity↗