Technical breakthroughs in the wearable artificial kidney (WAK)

Abstract

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.

Figure 1.

Schematics of the WAK. Blood drawn from a double lumen catheter (red) is anticoagulated with heparin from a reservoir (white) using a commercially available, battery-operated micro pump (ambIT, Sorenson, Salt Lake City, UT) and circulated through the blood channel of the WAK pump (gray) and into the dialyzer (AN-69 0.6 m². Hospal, France). The blood returns to the venous side of the double lumen catheter (blue). Clean dialysate (green) enters the dialyzer after an ambIT pump infuses a solution containing potassium, calcium, and magnesium from another reservoir (black). The dialysate circulates in countercurrent flow to the blood and exits (yellow) into the dialysate channel of the WAK pump. Another ambIT pump removes a predetermined amount of the spent dialysate (yellow) into a collection bag. The rest of the dialysate goes through a series of sorbent (yellow)- containing canisters (designed and built in our laboratory) containing urease, zirconium phosphate, hydrous zirconium oxide, and activated carbon. An ambIT pump infuses a solution containing sodium bicarbonate from a reservoir (brown) into the dialysate. The dialysate then returns to the dialyzer (green).

Figure 2.

The instantaneous blood flow waves of the WAK pump as recorded by flow-meter probes (Transonic Systems, Ithaca, NY) placed at the blood and dialysate tubing before the entrance to the pump and connected to Lab View virtual instruments (National Instruments, Austin, TX). Alternating peak and troughs flows of blood (red) and dialysate (green) are generated in opposite phase at 108 cycles/min.

Figure 3.

Instantaneous pressures at the blood and dialysate entrance ports for the WAK pump (upper panel) and conventional pump (lower panel). Pressure transducers were placed at the entrance and exit ports of both blood and dialysate in the dialyzers and hooked to the Lab View virtual instruments (National Instruments, Austin, TX).

Figure 4.

Instantaneous pressures at the blood and dialysate exit ports for the WAK pump (upper panel) and conventional pump (lower panel).

Figure 5.

Removal of urea by WAK system is shown to be a linear function of both parameters of dialysate flow: Average flow velocity and frequency of pulsation.

Figure 6.

As dialysate pH increases due to bicarbonate addition, there is enhanced extraction of urea from the dialysate as it is adsorbed onto the zirconium phosphate more effectively.

Figure 7.

Removal of β2M from healthy human blood by WAK system is shown to be most effective in the first half-hour.