M. Fels, âRecycle of dialysate from the artificial kidney by electro- chemical degradation of waste metabolites: Continuous reactor in- vestigations,â Med. Biol.
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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 38, NO. 11. NOVEMBER 1991
utilization remains. The urea oxidation region of 0.5 to 1.1 V relative to Ag/AgCI on Pt surfaces is nonspecific with respect to urea: other organic species which are contained in a physiologic buffer will also be oxidized. The data in Tables I and I1 show that initial glucose oxidation uses a significant portion of the curren:. Additional current is consumed through acetate oxidation. Acetate is a physiologic buffering agent used in many commercial dialysates. Evidence of acetate oxidation is seen through solution pH changes during the course of an experiment. Successive oxidations of glucose oxidation products also probably consume a major portion of the current. Confirmation of these speculations is required in order to determine how to maximize urea current utilization. Pending such confirmation, however, one possible remedy for improving urea current utilization is to limit the maximum potential of the W electrode to less than 1 . 1 V relative to Ag/AgCI. This will lower the amount of current going to glucose oxidation should not severely impact urea current utilization. It will, however, affect the ultimate size of the electrochemical reactor since the volumetric urea conversion rate will decrease.
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energ. (A section of J . Electroanal. Chem., vol. 174), vol. 13, pp.
15-24, 1985. [ I I ] S . J . Yao, and S. K. Wolfson Jr., “Cyclic controlled electrolysis,” U . S . Patent 4 603 006, May 5 , 1987. 1121 J. F. Patzer 11, S. J . Yao, S. K. Wolfson Jr., and R. Ruppel-Kerr, “Urea oxidation kinetics via cyclic voltammetry: Application to regenerative hemodialysis,” Bioelectrochem. Bioenerg., vol. 22, pp. 341-353, 1990. 1131 J. F. Patzer 11, S . K. Wolfson Jr., and S . J . Yao. “Reactor control and reaction kinetics for electrochemical urea oxidation,” Chem. Eng. S e . , vol. 45, pp. 2777-2784, 1990.
Correction to “A Model of the Stimulation of a Nerve Fiber by Electromagnetic Stimulation” Zahi A. Fayad, Bradley J. Roth, and Peter J. Basser Ther are two errors in the above paper,’ neither of which affects the main conclusions. The value of the inductance used to calculate
V . CONCLUSION
The VPR control method provides a simple, constant current control method for urea oxidation in physiologic buffers. The control method should provide improved, constant current control for any electrochemical reaction system that exhibits reversible W electrode deactivation due to oxidation products remaining on the surface and which must be maintained below a maximum potential limit. ACKNOWLEDGMENT R. Ruppel-Kerr performed the experimental work described in this paper. REFEREMCES U.S. Renal Data System, ”USRDS 1989 annual data report,” The Nat. Insti. Health, Nat. Insti. Diabetes and Digestive and Kidney Diseases. Bethesda, MD. 1989. J. H. Maxwell, and H. M. Sapolsky. “The first DRG: lessons from the end stage renal disease program for the prospective payment system,” Inquiry, vol. 24, pp. 57-67, 1987. M. Fels, “Recycle of dialysate from the artificial kidney by electrochemical degradation of waste metabolites: Continuous reactor investigations,” Med. Biol. Eng. Compui., vol. 20, pp. 257-263, 1982. J . C. Wright, A. C. Michaels, and A. J . Appleby, “Electrooxidation of urea at the ruthenium titanium oxide electrode,” AIChE J . , vol. 32, p. 1450, 1986. E. Klein, “Effects of disinfectants in renal dialysis patients,” Environ. Health Perspect., vol. 69, pp. 45-47, 1986. S . J . Yao, S. K. Wolfson Jr.. B. K. Ahn, and C . C. Liu, “Anodic oxidation of urea and an electrochemical approach to deureation,” Nature. vol. 241, pp, 471-472. 1973. R. W. Keller, Jr.. J. M. Brown, S . K. Wolfson Jr., and S . 1. Yao, “Intermittent potential reversal electrolysis for urea removal in hemodialysis,” in Pruc. IEEE/1980 Fronriers Eng. Healih Care, vol. 2, pp. 178-181, 1980. S . J. Yao, J . M. Brown, S.K. Wolfson Jr., K. V . Thrivikraman, and M. A. Krupper, “Controlled potential electrolysis for urea removal in hemodialysis: improved efficiency in urea clearance,” in Proc. 4th Annual Conf IEEE/1982 Froniiers Eng. Healih Care, Philadelphia, PA, vol. 4, 1982, pp. 24-27. S. J . Yao, S . K. Wolfson Jr., M. A. Krupper. and K. 1. Wu, “Controlled electrolysis of urea in biological fluids,” in Charge and Field Efects in Biosysiems, Allen MJ, Usherwood PNR, Eds. U.K.: Abacus, 1983, pp. 409-41 1 . -“Controlled-potential, controlled-currentelectrolysis: In vitro and in vivo electrolysis of urea urea removal,’’ Bioelecirochem. Bio-
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Fig. 8. (a) A three-dimensional plot of the response of the nerve fiber to electromagnetic stimulation just above threshold (V
