A Process for Enhancing Selectivity and Limiting Plugging in Plasmafractionation for Apob Removal

A new process using pressure and flow pulsations was investigated in the second stage of cascade filtration for ApoB removal. Due to enhanced filtration by the pulsations, the retentate flow vanished naturally without clamping the line, which reduced albumin and ApoA1 losses. The performance of Eval 4A and cellulose PF100 filters in this case were compared with that of classical dead end mode at a plasma flux of 18 ml/(min m2). The apparent sieving coefficient for small proteins (albumin, ApoA1) under pulsed conditions increased with increasing pressure instead of dropping as in dead end mode. In both cases the ApoB sieving coefficients remained below 0.02. These encouraging results were accompanied by a slower rise of transmembrane pressure showing a decrease of membrane plugging. Thus, the recovery of albumin and ApoA1 is increased while ApoB removal remains constant, which improves the selectivity of the fractionation stage.

Hemolysis Reduction in Plasmapheresis by Module Design: Operating with Pulsed Flow Filtration Enhancement

This study is an investigation into the effects of module design on hemolysis levels during the filtration enhancement of plasmapheresis using pulsed blood flow. Two polypropylene hollow fiber modules (F1 and F2) were compared under steady and pulsed flow conditions. The fiber lengths and membrane areas of the respective filters were 136 mm, 0.1 m2 and 226 mm, 0.25 m2 and were used at wall shear rates of 400 and 600 s-1. Fresh citrated bovine blood was circulated at 90 ml/min through their fibers with permate and retentate being recirculated. Plasma samples were analysed by the Cripps method to obtain the mean free hemoglobin concentration. A comparison of the average hemoglobin released with time per fiber, and per unit length allowed an assessment of the effects of fiber length and shear rate on hemolysis levels. It was concluded that a reduction in area and fiber length would reduce hemolysis levels and design equations are suggested to find the optimum length.

An experimental and numerical study of the flow and mass transfer in a model of the wearable artificial kidney dialyzer

BACKGROUND

Published studies of the past decades have established that mass transfer across the dialyzer membrane is governed by diffusion, convection and osmosis. While the former is independent of the pressure in the liquids, the latter two are pressure dependent and are enhanced when the pressure difference across the membrane is increased. The goal of the present study is to examine the impact of pulsatile flow on the transport phenomena across the membrane of a high-flux dialyzer in a wearable artificial kidney (WAK) with a novel single small battery-operated pulsatile pump that drives both the blood and dialysate in a counter-phased manner, maximizing the trans-membrane pressure.

METHODS

Both in-vitro experimental and numerical tools are employed to compare the performance of the pulsatile WAK dialyzer with a traditional design of a single-channel roller blood pump together with a centrifugal pump that drives the dialysate flow. The numerical methods utilize the axisymmetric Navier-Stokes and mass transfer equations to model the flow in the fibers of the dialyzer.

RESULTS

While diffusion is still the dominating transport regime, the WAK pump enhances substantially the trans-membrane pressure and thus increases mass convection that might be as high as 30% of the overall transfer. This increase is obtained due to the design of the pulsatile WAK pump that increases ultrafiltration by increasing the trans-membrane pressure.

CONCLUSIONS

The experimental and numerical results revealed that when pumping at similar flow rates, a small battery-operated pulsatile pump provides clearances of urea and creatinine similar as or better than a large heavy AC-powered roller pump.

Technical breakthroughs in the wearable artificial kidney (WAK)

BACKGROUND

The wearable artificial kidney (WAK) has been a holy grail in kidney failure for decades. Described herein are the breakthroughs that made possible the creation of the WAK V1.0 and its advanced versions V 1.1 and 1.2.

DESIGN

The battery-powered WAK pump has a double channel pulsatile counter phase flow. This study clarifies the role of pulsatile blood and dialysate flow, a high-flux membrane with a larger surface area, and the optimization of the dialysate pH. Flows and clearances from the WAK pump were compared with conventional pumps and with gravity steady flow.

RESULTS

Raising dialysate pH to 7.4 increased adsorption of ammonia. Clearances were higher with pulsatile flow as compared with steady flow. The light WAK pump, geometrically suitable for wearability, delivered the same clearances as larger and heavier pumps that cannot be battery operated. Beta(2) microglobulin (beta(2)M) was removed from human blood in vitro. Activated charcoal adsorbed most beta(2)M in the dialysate. The WAK V1.0 delivered an effective creatinine clearance of 18.5 +/- 3.2 ml/min and the WAK V1.1 27.0 +/- 4.0 ml/min in uremic pigs.

CONCLUSIONS

Half-cycle differences between blood and dialysate, alternating transmembrane pressures (TMP), higher amplitude pulsations, and a push-pull flow increased convective transport. This creates a yet undescribed type of hemodiafiltration. Further improvements were achieved with a larger surface area high-flux dialyzer and a higher dialysate pH. The data suggest that the WAK might be an efficient way of providing daily dialysis and optimizing end stage renal disease (ESRD) treatment.

Effects of operating conditions on selectivity of a plasma fractionator in double filtration plasmapheresis

In a typical double filtration plasmapheresis treatment, plasma fractionation between albumin and some immunoglobulins associated with toxins is limited because none of the currently available plasma fractionators has a strict cutoff property for these proteins. Selectivity of immunoglobulins over albumin depends not only on the cutoff properties of the membrane but on the operating conditions such as the flow rate of the supplied plasma (Q(P)) and retained plasma to be discarded (Q(D)) in the plasma fractionator. We carried out an in vitro study using human plasma harvested by single plasma exchange treatments to assess the selectivity of a plasma fractionator, Evaflux 2A-F (Kawasumi Laboratories, Inc., Tokyo, Japan), under various operating conditions. The results of rate-constant filtration experiments showed that the concentrations in the feed tank and the sieving coefficient (SC) values of every protein were decreased slightly within 2 h after the start of the experiment because of membrane trapping, adsorption, and/or plugging. The time-averaged SC value of albumin increased with flow rate ratio (Q(P)/Q(D)) due to increasing filtration fraction (FF), but relative removal efficiency (mD/mP*) for albumin decreased with Q(P)/ Q(D) due to decreasing Q(D). For immunoglobulins, on the other hand, the SC values were almost unchanged, and the mD/mP* values increased with Q(P)/Q(D) due to an increase in FF. Both increasing Q(P) and decreasing Q(D) are effective means of improving selectivity between these proteins in the plasma fractionator. Membrane fouling is, however, obvious beyond a Q(P)/Q(D) value that is thought to be a critical point. Operation should be conducted below the critical Q(P)/Q(D) value, which depends on the patient's plasma components and the cutoff property of the membrane.

The acu-men: a new device for continuous renal replacement therapy in acute renal failure

BACKGROUND

We sought to design a simple machine to safely provide continuous veno-venous hemofiltration to acute renal failure patients.

RESULTS

The acu-men device uses a pneumatic blood pump with tidal blood flow as the driving force. A volumetric balancing system balances the filtrate with the replacement fluid, and the blood-air interface is eliminated by replacing the conventional venous drip chamber with two air-separating membranes. The extracorporeal circuit is integrated in a disposable cartridge, which is inserted into the machine at the beginning of treatment. The priming and rinsing is done automatically.

CONCLUSION

While preliminary data from an ongoing clinic trial on the efficacy of the device are encouraging, further long-term studies are necessary to evaluate its potential to decrease morbidity and mortality in acute renal failure patients.

A high selectivity cascade filtration technique for LDL-cholesterol and Lp(a) removal

This work proposes an improvement of the cascade filtration technique in the treatment of familial hypercholesterolemia. A model of the whole process permitted the definition of the parameters that could influence the selectivity of the fractionation: the pore size, the sieving coefficients of both fractionation and plasmapheresis membrane, and the final retentate flow rate. In vivo studies have shown that the dead-end mode for the secondary filter was not always practical because of severe membrane plugging except when a pulsatile pump was included in the extracorporeal circuit. This pump generated hydrodynamic instabilities which decreased membrane fouling and retarded the build up of the polarization concentration layer. Optimization of these specific operating conditions permitted increase in the selectivity index from 1.15 to 2.24. The performances of cascade filtration were then comparable to those of adsorption on dextran sulfate columns.