Development of a Multifunctional 22-Channel Functional Electrical Stimulator for Paraplegia

Ross Davis, T. Johnston, B. Smith, R. Betz, T. Houdayer, A. Barriskill

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

Abstract

54.1 Introduction e authors’ aim has been to develop a generic functional electrical stimulation (FES) implant for the restoration of functions in spinal cord-injured (SCI) paraplegic individuals, the functions or modes of which can be matched to an individual’s requirements: upright functional mobility, pressure relief and lower extremity exercise, and bladder and bowel control [1-6]. In addition, for bladder control, less invasive surgical procedures were proposed to avoid posterior conus rhizotomy, and sacral lami notomy to access the sacral nerve roots for stimulation [7, 8]. It was hoped that this system would oer more functions and less surgery to patients with a cost-benet ratio. is approach was termed “Multi-Functional.” Simple locomotor functions can complement the use of a wheelchair and can be helpful in overcom ing obstacles to wheelchair access, especially doorsteps and unadapted bathroom facilities. In addition, being able to stand up to reach objects and perform prolonged manual tasks would be convenient for many workplace and home situations [3-5]. Five paraplegic volunteers (two at the Neural Engineering Clinic (NEC) in Augusta, ME and three at the Shriners Hospital for Children (SHC) in Philadelphia, Ross Davis Florida Institute of Technology T. Johnston Shriners Hospital for Children B. Smith Shriners Hospital for Children R. Betz Shriners Hospital for Children T. Houdayer Neural Engineering Clinic A. Barriskill Neopraxis Pty. Ltd. During 1983, R.D. (NEC) became aware of the possibilities of modifying and using the 22-channel cochlear implant technology (Cochlear Ltd., Lane Cove, N.S.W., Australia) as the basis for an implant able FES system for the restoration of multiple functions in SCI paraplegics. e state of FES in paraplegia has been extensively reviewed [1-5]. ese SCI individuals are unable to move their lower extremities or control bladder and bowel function. ey must regularly self-cath eterize (~3-6 times per day). Secondary medical problems are prone to occur, such as pressure sores, osteoporosis, muscular atrophy in the lower limbs, muscle spasticity, deep-vein thrombosis, cardiovas cular disease, and depression. Although considerable FES achievements have been made, there has yet to be developed a safe, practical FES system for these multiple functions that is completely independent of the laboratory and is an energy-ecient mobility aid for prolonged use at home and in the workplace. e reason lies in the fact that FES is addressing complex problems requiring not only interdisciplinary knowledge from muscle and nerve physiology and electrical stimulation technology but also the imple mentation of biomechanical and control principles [6]. Other reasons that limit clinical application may also be signicant, for example, cost-benet con siderations (especially for implanted systems). Although spinal injury results in the loss of multiple physiological systems, neural implants to date have been developed to restore only specic functions. An approach was proposed to develop a generic FES implant, the functions or modes of which can be matched to an individual patient’s requirements. In addition, less invasive surgical procedures were proposed to avoid the posterior conus rhizotomies and sacral laminectomy associated with the existing implanted bladder implants [7, 8]. Since 1984, three FES implant models have evolved from the Cochlear’s technology and its subsid iary: Neopraxis Pty. Ltd. e initial Nucleus FES-22 stimulator was implanted in 1991 aer animal and human studies, and with the U.S. Food and Drug Administration’s approval (IDE# G87014) and Institutional Review Board (IRB) approval in 21-year-old paraplegic subject (ASIA: T10). 54.2 Historical Aspect In 1984, the Veterans Administration (VA) funded the initial animal studies at the Togus VA Medical Center (Augusta, ME). ese were aimed at determining what changes would be required to use a modi ed cochlear implant with a maximum pulse output of 4.3 mA and 0.4 ms pulse width to be suitable for FES use in humans. An initial decision was taken to utilize epineurally placed electrodes (2.5-mm diameter platinum disks) in preference to epimysial or intramuscular electrodes because it was known that the stimulation currents would be lower and that there would be less movement of the electrodes. To determine exactly how low the stimulation currents would be and to determine the stimulation sites, initial anesthetized rabbits studies were conducted [9]. e threshold found for each branch of the split sciatic nerves was 0.1-0.2 mA at 0.2 ms with 50 pps. e maximal stimulation was achieved usually between 0.5 and 1.0 mA. Simultaneous dorsiexion of both paws as well as cocontraction in the anterior and posterior muscle groups could be achieved. At the Togus VA Medical Center, with the approval of the IRB and volunteer patients undergo ing lower extremity ampu tation, stimulation studies were carried out at 0.2 ms pulse duration with 20 pps frequency, with a portable, battery-operated, and calibrated constant-current unit (Cordis Corp., Miami, FL, Model 910 A). e pulse amplitudes for producing maximal stimulation and contraction in the largest of the nerves (medial sciatic) ranged from 0.6 to 2.5 mA, which falls well within the range of the Cochlear receiver-stimulating unit to be used [9, 10]. Using the Color Atlas of Human Anatomy, First Edition edited by R. M. H. McMinn and R. T. Hutchings (Yearbook Medical Publishers, Inc., Chicago, IL), whose dissections were reproduced as life-size photographs, allowed measurements of the diameters to be made at dierent points along the nerves. ese measurements were in relatively close agreement with the amputated nerve diameters of the nine volunteer patients [10]. 54.3 Neural Engineering Clinic: Two Male Subjects 54.3.1 Nucleus FES22 Stimulating System As a rst device, the FES22 stimulator was only intended to provide its recipient with enhanced mobil ity functions. During 1985, Roger Avery (Custom Med Laboratories, Durham, NH) started work on the design and manufacture for the implantable leads and electrodes. Because of the need for higher output currents, it was also necessary to design a new transmitter coil capable of delivering the higher power. To make each of the 22-output channels individually available, a circular epoxy housing was designed with 22 sockets around the perimeter (Figure 54.1a) with the diameter of the housing being determined by the diameter of the coil. During November/December 1991, the Nucleus FES-22 system was implanted in sub ject A (21-year-old male paraplegic subject; ASIA: A T10) in three sessions at the Kennebec Valley Medical Center (now Maine General Medical Center), Augusta, ME. e receiver-stimulator was placed subcuta neously at the lower right anterior intercostal margin with 11 connecting leads subcutaneously tunneled to the right and another 11 subcutaneously tunneled to the le hip areas. Following this, 2.5-mm-diameter platinum disk electrodes were placed epineurally on the individual branches of the right and le femoral nerves by suturing the silicone elastomer ring around each electrode to the connective tissues on each side of the nerve branches. In the second and third procedures, electrodes were attached over gluteal, posterior tibial, peroneal, and sciatic nerves bilaterally [11]. A total of 20 electrodes were implanted epineurally, with one electrode placed subcutaneously in a Teon bag in each of the femoral triangles, as the spare lead. Six weeks following surgery (January 1992), the FES-22 system did produce threshold and maximal muscle contractions as tested in all 20 channels. At the second testing session in February 1992, the implanted system did not function properly owing to a suspected electrostatic damage in the implant, resulting in the loss of seven channels. Hardware and soware changes were made allowing the remain ing 15 channels to work. In December 1992, the 15 channels were retested for threshold and maximal muscle contractions; the multivariate analysis did not show any change with time or body side, but a signicant eect was seen with the electrode locations [12].

Original languageEnglish
Title of host publicationBiomedical Engineering Fundamentals
PublisherCRC Press
Pages54-1-54-11
ISBN (Electronic)9781439825198
DOIs
StatePublished - 1 Jan 2014
Externally publishedYes

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