Characterization of High Surface Area Electrodes for Safe Delivery of Charge Balanced Direct Current for Nerve Conduction Block Tina L. Vrabec Member, IEEE, Niloy Bhadra Member, IEEE, Jesse S. Wainright, Narendra Bhadra, Manfred Franke and Kevin L. Kilgore
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ANY neurological diseases and conditions are characterized by undesirable neural activity which can give rise to severe symptoms such as spasticity or chronic pain. A conduction block that is localized, fast acting and reversible is necessary to meet the needs of patients exhibiting these conditions. Kilohertz high frequency alternating current (KHFAC) has been used to cause a fast acting, reversible conduction block [1]. However, a short but intense firing at the initiation of KHFAC referred to as the “onset response” hinders the application of KHFAC [1]. Direct current (DC) applied during the initiation of KHFAC has been established as a possible method for inhibiting the onset activity [2]. This application of DC unfortunately causes a reduction in conduction when applied for a long enough time to inhibit the onset activity [2]. The combination of a charge balancing waveform and high surface area electrodes has enabled the use of longer DC pulses without a reduction in the nerve conduction.
Due to the production of toxic electrochemical products during prolonged DC delivery, the nerve tissue can be damaged. Previously it has been demonstrated that an electrode design that separates the tissue from these products can protect the nerve during prolonged DC delivery [3]. If the stimulation parameters are chosen so that the electrode operates only within its water window it is possible to prevent the creation of electrochemical products altogether. Various electrode coatings can be used to increase the capacitance of the electrode while maintaining the same electrode size (e.g., platinum black, iridium oxide). This allows more charge to be delivered while maintaining the electrode potential within the water window [4] which expands the amount of time that DC current that can be safely delivered. In vivo experiments were performed on the sciatic nerve of rats to compare the characteristics and safety of high surface area electrodes to smooth platinum electrodes. The DC waveform delivered was a charge balanced waveform with a cathodic (blocking) pulse chosen to stay within the water window followed by an anodic recharge phase which returned 100% of the charge. Electrode potentials were recorded in vivo to demonstrate that the potentials remained within the water window and to further characterize the capacitance of the electrode (figure 1). Nerve health was determined through force measurements of the muscle resulting from stimulus electrodes proximal and distal to the blocking site. The DC delivery was Figure 1: in vivo potential measurements cycled to determine the amount of DC that could safely be delivered. Prolonged DC delivery (over 100 cycles) was possible if the parameters were chosen to stay within the water window. This allows for the safe usage of DC to mitigate the onset response due to KHFAC stimulation. REFERENCES [1] [2] [3] [4]
N. Bhadra, K.L. Kilgore, “High-frequency electrical conduction block of mammalian peripheral motor nerve,” Muscle Nerve, vol. 32, pp. 782–790, 2005 D.M. Ackermann Jr, N. Bhadra, E.L. Foldes, K.L. Kilgore. “Conduction block of whole nerve without onset firing using combined high frequency and direct current.” Med Biol Eng Comput. 2011 Feb;49(2):241-51. Epub 2010 Oct 2. D. Ackermann, N. Bhadra, E Foldes, K. Kilgore, “Separated interface nerve electrode prevents direct current induced nerve damage” Journal of Neuroscience Methods pp 173-176 2011 S. Cogan, J. Ehrlich, T. Plante, A Smirnov,1 D. Shire, M. Gingerich, J. Rizzo, “Sputtered Iridium Oxide Films for Neural Stimulation Electrodes”,Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2008
*Research supported by National Institutes of Health, NINDS 1R01-NS074149. T. L. Vrabec is with Case Western Reserve University 10900 Euclid Ave., Cleveland, Ohio 44106 (phone: 440-749-7628 Fax: email:
[email protected]) N. Bhadra is with Case Western Reserve University 10900 Euclid Ave., Cleveland, Ohio 44106 (email:
[email protected]) N. Bhadra is with Case Western Reserve University 10900 Euclid Ave., Cleveland, Ohio 44106 (email:
[email protected]) J. S. Wainright is with Case Western Reserve University 10900 Euclid Ave., Cleveland, Ohio 44106 (email:
[email protected]) M. Franke is with Case Western Reserve University 10900 Euclid Ave., Cleveland, Ohio 44106 (email:
[email protected]) K. L. Kilgore is with Case Western Reserve University 10900 Euclid Ave., Cleveland, Ohio 44106; MetroHealth Medical Center 2500 MetroHealth Dr Cleveland, OH 44109; and Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, Ohio, 44106 (email:
[email protected])
