Battery-Powered Implantable Nerve Stimulator for Chronic Activation of Two Skeletal Muscles Using Multichannel Techniques

Chronic activation of skeletal muscle is used clinically in representative numbers for diaphragm pacing to restore breathing and for dynamic graciloplasty to achieve fecal continence. The 3 different stimulation techniques currently used for electrophrenic respiration (EPR) all apply high frequency powered implants. It was our goal to make these stimulation methods applicable for EPR by a battery-powered nerve stimulator that would maximize the patient's freedom of movement. Additionally, the system should allow the implementation of multichannel techniques and alternating stimulation of 2 skeletal muscles as a further improvement in graciloplasty. Generally, the developed implantable nerve stimulator can be used for simultaneous and alternating activation of 2 skeletal muscles. Stimulation of the motor nerve is achieved by either single channel or multichannel methods. Carousel stimulation and sequential stimulation can be used for graciloplasty as well as for EPR. For EPR we calculated an operating time of the implant battery of 4.1 years based on the clinically used stimulation parameters with carousel stimulation. The multichannel pulse generator is hermetically sealed in a titanium case sized 65 x 17 mm (diameter x height) and weighs 88 g.     

Multielectrode Nerve Cuff Stimulation of the Median Nerve Produces Selective Movements in a Raccoon Animal Model

Abstract

In this study, an electrode system consisting of twelve small platinum dot electrodes imbedded in a spiral silicone rubber insulating cuff was used to investigate the feasibility of selective (regional) stimulation of the median nerves of the raccoon. Acute experiments in four raccoons consisted of functional response observations, isometric force recordings from tendon attachments and postmortem fascicular mapping. Functional responses (elbow, wrist and/or digit flexion, pronation and/or thumb abduction) to selective stimulation were noted as dependent upon cuff electrode configuration (longitudinal tripole with and without field steering, as well as a transverse bipolar arrangement) and current level (threshold, 1/2 maximal, maximal). Muscle force recruitment curves (force as a function of stimulus amplitude) were plotted for flexor digitorum superficialis, flexor digitorum profundus, flexor carpi radialis, palmaris longus and pronator teres of three raccoons. Fascicular maps at the level of the nerve cuff were created indicating the approximate position of innervation to each of the aforementioned muscles, as well as other innervation such as paw fascicles, sensory fascicles, and elbow innervation (such as coracobrachialis). The greatest selectivity was observed at or near threshold current levels. In all tour raccoons studied, a threshold electrode choice and stimulation strategy could be identified enabling selective production of either digit flexion, wrist flexion and/or digit and wrist flexion. It was possible to elicit a selective pronation response at threshold in three of the four animals. Selective elbow flexion at threshold could be produced in all four experiments. With stronger currents, additional movements were usually induced. The raccoon therefore appears to be a suitable, if challenging, animal model for further development of not only nerve cuff electrode approaches but perhaps other stimulation electrode technologies prior to human neuroprosthetic studies. (J Spinal Cord Med 1997; 20:233-243)     

A prospective multicentre study to investigate percutaneous tibial nerve stimulation for the treatment of faecal incontinence

Aim Percutaneous tibial nerve stimulation (PTNS) is a minimal invasive treatment that can be performed in the outpatient clinic. This is a pilot study to investigate PTNS in the treatment of faecal incontinence. Method Percutaneous tibial nerve stimulation was performed by insertion of a needle electrode near the posterior tibial nerve. Patients were treated twice a week. Evaluation of faecal incontinence and quality of life was performed at baseline, 6 weeks, 3 months, 6 months and 1 year. Quality of life was estimated using SF‐36 and FIQL questionnaires. Results A total of 22 patients were included. The mean age was 60.4 ± 11.7 years. After 6 weeks, 18 continued the treatment; 13 patients had a > 50% decrease in incontinence episodes. Overall incontinence episodes fell from 19.6 ± 21.0 at baseline to 9.9 ± 15.5 (P = 0.082) at 6 weeks and to 3.6 ± 4.8 (P = 0.029) at 1 year. Postponement time and quality of life increased significantly during follow up. Conclusion Percutaneous tibial nerve stimulation is simple and can be used in the outpatient setting. Good results can be obtained and sustained during maintenance treatment.     

The Effect of Electrode Placement and Interphase Interval on Force Production During Stimulation of the Dorsiflexor Muscles

The aims of this study were to investigate whether introducing an interphase interval (IPI) to biphasic pulses during stimulation of the dorsiflexor muscles would affect force production and to determine whether the IPI effect is dependent on electrode position. Twelve healthy volunteers participated in the study. Each subject participated in one session during which electrically induced contraction (EIC) forces of the ankle dorsiflexors were measured with five different IPI settings ranging from 0 to 400 μs. Forces of EICs were assessed with the electrodes placed either with the proximal electrode positioned over the common peroneal nerve and the second electrode over the dorsiflexor muscles or with both electrodes located over the dorsiflexor muscles. The order of electrode placements and of the different IPI settings was randomized across subjects. The results indicated that the introduction of a 100‐μs‐long IPI may enhance force production when one electrode is located over the common peroneal nerve. However, increasing the duration of the IPI beyond 100 μs did not result in further increase in force production. In contrast, the introduction of an IPI did not increase force production when both electrodes were located over the dorsiflexor muscles. These findings may help to optimize stimulation settings during functional electrical stimulation to prevent foot‐drop.     

Impact of direct epispinal stimulation on bladder and bowel functions in pigs: A feasibility study

Aims

This study assesses the potential of epispinal (subdural) stimulation application in the treatment of urinary and bowel neurological disorders. Acute experiments were performed on a large animal model — the domestic pig — to develop a new methodology facilitating future results and technology transfers to human.

Methods

After rectal and bladder catheterization, four Landrace pigs (45‐50 kg) underwent spinal cord surgery — that is, lumbosacral incision, laminectomy [L4‐S4], dural opening and microsurgical arachnoid dissection. Three successive electrical stimulation sessions were carried out: 1) nerve roots stimulation, 2) epispinal stimulation with a matrix electrode, 3) epispinal stimulation with a small diameter needle electrode. Changes in rectal and bladder pressures were monitored throughout the various procedures to identify spinal areas inducing responses while evaluating the influence of electrode contacts size in the measured responses amplitudes.

Results

An interesting area was identified in the upper portion of the spinal myelomeres (ie, spinal cord segment delimited by two successive pairs of spinal roots) directly adjoining root with best pressures (either rectal or vesical). Significant responses (up to 40 cmH₂O) were also obtained with a needle electrode. Furthermore, bowel evacuation was triggered in one of the animals. Despite the use of smaller electrode contacts, no detrusor or rectum selective responses were observed in none of the sessions.

Conclusion

This study showed, for the first time, that epispinal stimulation causes significant detrusor and rectal responses in pigs and allows considering further studies with the objective of treating urinary and rectal disorders in spinal cord injury patients.     

Comparison of respiratory sparing effect between pancuronium and three new nondepolarizing muscle relaxants in rats

Purpose There is a large difference in sensitivity between respiratory muscles and other limb muscles. This phenomenon, known as the respiratory sparing effect (RSE), is well established withd-tubocurarine, pancuronium, and succinylcholine. The purpose of this study is to evaluate the RSE of these new relaxants, vecuronium, pipecuronium, and ORG9426. Methods The study was done in vivo using rats. Mechanical twitch responses of tibialis anterior muscle and diaphragm stimulated with the sciatic nerve and phrenic nerve, respectively, were recorded simultaneously to monitor neuromuscular transmission. Changes of mechanical twitch responses from both muscles were compared following the injection of four kinds of muscle relaxants (pancuronium, picuronium, recuronium, and ORG9426). Results T, D (%) represents the maximum depression in tibialis anterior and diaphragm, respectively. T−D (%), which means the sensitivity difference between the two kinds of muscle, was calculated by subtracting D from T. The T−Ds of pancuronium, pipecuronium, vecuronium, and ORG9426 were 86.0±2.6%, 81.4±1.9%, 77.7±2.1%, and 74.6±2.7%, respectively. Conclusions The results indicated that the blockade produced by each muscle relaxant was lower in the diaphragm than in the anterior tibialis muscle. T−D was significantly smaller with vecuronium or ORG9426 than with pancuronium.     

Fascicular anatomy and surgical access of the human pudendal nerve

The ability to access selectively distal nerve branches at the level of the compound pudendal nerve (PN) would allow control of multiple neural pathways and genitourinary functions at a single location. Nerve cuff electrodes can selectively stimulate individual fascicles; however the PN fascicular anatomy is unknown. The fascicular representation of distal branches was identified and traced proximally to create fascicle maps of 12 compound PNs in seven cadavers. Distal nerves were represented as groups of individual fascicles in the PN. Fascicle maps were consistent between specimens and along the PN within specimens. PN branch free length was 26±7.7 mm. PN cross-sections were relatively flat with major and minor diameters of 4.3±0.90 and 1.7±0.45 mm, respectively. Placing a nerve cuff on the PN is anatomically and surgically feasible. The PN fascicular anatomy, branch free length, and cross-section geometry are conducive to selective stimulation of distal nerves with a single nerve cuff electrode.     

Stimulation of abdominal and upper thoracic muscles with surface electrodes for respiration and cough: Acute studies in adult canines

Objective: To optimize maximal respiratory responses with surface stimulation over abdominal and upper thorax muscles and using a 12-Channel Neuroprosthetic Platform.

Methods: Following instrumentation, six anesthetized adult canines were hyperventilated sufficiently to produce respiratory apnea. Six abdominal tests optimized electrode arrangements and stimulation parameters using bipolar sets of 4.5?cm square electrodes. Tests in the upper thorax optimized electrode locations, and forelimb moment was limited to slight-to-moderate. During combined muscle stimulation tests, the upper thoracic was followed immediately by abdominal stimulation. Finally, a model of glottal closure for cough was conducted with the goal of increased peak expiratory flow.

Results: Optimized stimulation of abdominal muscles included three sets of bilateral surface electrodes located 4.5?cm dorsal to the lateral line and from the 8^th intercostal space to caudal to the 13^th rib, 80 or 100?mA current, and 50?Hz stimulation frequency. The maximal expired volume was 343 ± 23?ml (n=3). Optimized upper thorax stimulation included a single bilateral set of electrodes located over the 2^nd interspace, 60 to 80?mA, and 50?Hz. The maximal inspired volume was 304 ± 54?ml (n=4). Sequential stimulation of the two muscles increased the volume to 600 ± 152?ml (n=2), and the glottal closure maneuver increased the flow.

Conclusions: Studies in an adult canine model identified optimal surface stimulation methods for upper thorax and abdominal muscles to induce sufficient volumes for ventilation and cough. Further study with this neuroprosthetic platform is warranted.     

Evaluation of a Thin-film Peripheral Nerve Cuff Electrode

Abstract

This is a study of the reaction of large nerves to implantation using a flexible, thin-film cuff electrode. Cuff electrodes were implanted on the sciatic nerve of three cats. An implantation period of six weeks allowed sufficient time for any injury responses in the nerve and connective tissue sheath around the cuff to develop. The electrode came off the nerve in one of the cats. In the remaining two cats, gross observation following explantation of the electrodes revealed encapsulation of the cuffs without swelling of nerve tissue. Histological evaluation did not demonstrate nerve injury. The nerve cuff electrodes, which are comprised of titanium and iridium coatings on a fluorocarbon polymer substrate, appeared unaffected by the implantation, and connective tissue encapsulation did not adhere to either the polymer substrate or metallization. Evaluation of the electrodes using activated iridium oxide charge injection sites in more extended studies is now being undertaken. (J Spinal Cord Med; 18:28–32)     

Study of the silent period following motor evoked potential by magnetic stimulation method

During the voluntary contraction of target muscles, a silent period is observed immediately after the motor evoked potential (MEP) is elicited by transcranial magnetic stimulation. In this study, the silent period was recorded from bilateral abductor digiti minimi (ADM) and abductor hallucis (AH) in 30 normal healthy subjects (120 extremities) and 30 patients with cervical myelopathy (120 extremities). In normal subjects, the silent period was 142.3±41.0 ms (mean±SD) for ADM, and 83.6±42.3 ms for AH. When stimulus intensity was increased from 60% to 95%, the length of the silent period increased, reaching almost maximal level. The length of the silent period correlated with stimulus intensity, but not with the contraction force of voluntary muscles. In patients with cervical myelopathy, the silent period was 69.2±27.8 ms (mean±SD) for ADM and 48.3±17.0 ms for AH, significantly shorter than in the normal subjects. We believe that the length of the silent period can be a useful parameter for indicating the function of the spinal inhibitory system. This work was presented, in part, at the 9th Annual Orthopaedic Research Meeting of the Japanese Orthopaedic Association, Kobe, Japan, 7–8 October 1994, and at the Xth International Congress of EMG and Clinical Neurophysiology, Kyoto, Japan, 15–19 October 1995.     

Evaluation of the Efficacy and Robustness of a Second Generation Implantable Stimulator in a Patient With Hemiplegia During 20 Years of Functional Electrical Stimulation of the Common Peroneal Nerve

We evaluated the efficacy and robustness of a second generation implantable stimulator for correcting drop foot (DF) in a patient with left‐sided hemiplegia over 20 years of functional electrical stimulation (FES) of the common peroneal nerve (CPN). Dorsal flexion and eversion of the affected foot was partially restored by FES of the superficial region of the CPN innervating mostly the tibialis anterior (TA) and partly peroneus longus (PL) and peroneus brevis (PB) muscles. The reasons for implant failure during the long‐term follow‐up assessment were analyzed and resolving procedures were identified. The stimulator had an average failure rate of once every three years, due to repetitive mechanical load on the lead wires of its internal and/or external unit, and had to be serviced once per year to replace the heel switch integrated into the shoe sole. FES‐associated mechanical trauma to the CPN elicited a thickening of the connective tissue around the CPN and a slightly compromised conduction velocity of the CPN. FES of the CPN, with the second generation implantable stimulator, improved gait parameters of the affected leg during the 20 years period. Long‐term, daily FES enables a functional and reliable recruitment of nerve fibers, thus providing a sufficient dorsal flexion and optimal eversion of the affected foot to sustain unassisted, almost normal gait. Therefore, the presented implant is suitable for very long‐term FES of the CPN.     

A new minimally invasive technique for pudendal nerve stimulation1

Aim Pudendal nerve stimulation (PNS), which is an alternative to sacral nerve stimulation, requires neurophysiological confirmation of correct siting of the electrode. We describe a modification of the existing technique where placement is assisted by guidance to the ischial spine by a finger introduced per anum. Method Cadaveric dissection was carried out to confirm the accuracy of this new approach. The surface marking of the ischial spine is marked. A stimulating needle electrode inserted through a skin incision at this point, is advanced towards the ischial spine using a finger introduced per anum as a guide. Once effective stimulation of the pudendal nerve is confirmed by observed and palpated contraction of the anal musculature, a permanent stimulating electrode is inserted and the position confirmed by radiological screening. Results Using cadaveric studies, the correct surface markings for needle placement were confirmed. This technique was then applied successfully for in vivo insertion of the needle electrode in 20 patients with bowel dysfunction, with only one lead displacement occurring over a mean follow‐up period of 12 months. Conclusion Finger‐guided assistance of PNS electrode insertion is simple and reproducible without requiring neurophysiological confirmation of nerve stimulation to ensure correct lead location.     

The recruitment of bone marrow‐derived cells to skin wounds is independent of wound size

Wounded skin recruits progenitor cells, which repair the tissue defect. These cells are derived from stem cells in several niches in the skin. In addition, bone marrow‐derived cells (BMDCs) are recruited and contribute to wound repair. We hypothesized that larger wounds recruit more cells from the bone marrow. Wild‐type rats were lethally irradiated and transplanted with bone marrow cells from green fluorescent protein (GFP)‐transgenic rats. Seven weeks later, 4, 10, and 20 mm wounds were created. The wound tissue was harvested after 14 days. The density of GFP‐positive cells in the wounds and the adjacent tissues was determined, as well as in normal skin from the flank. Bone marrow‐derived myofibroblasts, activated fibroblasts, and macrophages were also quantified. After correction for cell density, the recruitment of BMDCs (23±11%) was found to be independent of wound size. Similar fractions of GFP‐positive cells were also detected in nonwounded adjacent tissue (29±11%), and in normal skin (26±19%). The data indicate that BMDCs are not preferentially recruited to skin wounds. Furthermore, wound size does not seem to affect the recruitment of BMDCs.     

Effect of avanafil on rat and human corpus cavernosum

We compared the activity of a new phosphodiesterase‐5 inhibitor (PDE5i) avanafil with sildenafil and tadalafil in human and rat corpus cavernosum (CC) tissues. The effect of avanafil with several inhibitors and electrical field stimulation (EFS) was evaluated on CC after pre‐contraction with phenylephrine. With the PDE5i, sildenafil and tadalafil, concentration–response curves were obtained and cyclic guanosine monophosphate (cGMP) levels were measured in tissues. Avanafil induced relaxation with maximum response of 74 ± 5% in human CC. This response was attenuated by NOS inhibitor and soluble guanylate cyclase (sGC) inhibitor. Avanafil potentiated relaxation responses to acetylcholine and EFS in human CC and enhanced SNP‐induced relaxation and showed 3‐fold increase in cGMP levels. When compared with sildenafil, avanafil and tadalafil were effective at lower concentrations in human CC. In addition, Sprague–Dawley rats underwent in vivo intracavernosal pressure (ICP) and mean arterial pressure (MAP) measurements. Avanafil increased ICP/MAP that was enhanced by SNP and cavernous nerve (CN) stimulation in rat CC tissues. Also avanafil showed maximum relaxation response of 83 ± 7% in rat CC with 3‐fold increase in cGMP concentration. Taken together, these results of our in vivo and in vitro studies in human and rat suggest that avanafil promotes the CC relaxation and penile erection via NO‐cGMP pathway.     

Improvement of peripheral nerve regeneration in acellular nerve grafts with local release of nerve growth factor

Previous studies have demonstrated the potential of growth factors in peripheral nerve regeneration. A method was developed for sustained delivery of nerve growth factor (NGF) for nerve repair with acellular nerve grafts to augment peripheral nerve regeneration. NGF‐containing polymeric microspheres were fixed with fibrin glue around chemically extracted acellular nerve grafts for prolonged, site‐specific delivery of NGF. A total of 52 Wister rats were randomly divided into four groups for treatment: autografting, NGF‐treated acellular grafting, acellular grafting alone, and acellular grafting with fibrin glue. The model of a 10‐mm sciatic nerve with a 10‐mm gap was used to assess nerve regeneration. At the 2nd week after nerve repair, the length of axonal regeneration was longer with NGF‐treated acellular grafting than acellular grafting alone and acellular grafting with fibrin glue, but shorter than autografting (P < 0.05). Sixteen weeks after nerve repair, nerve regeneration was assessed functionally and histomorphometrically. The percentage tension of the triceps surae muscles in the autograft group was 85.33 ± 5.59%, significantly higher than that of NGF‐treated group, acellular graft group and fibrin‐glue group, at 69.79 ± 5.31%, 64.46 ± 8.48%, and 63.35 ± 6.40%, respectively (P < 0.05). The ratio of conserved muscle‐mass was greater in the NGF‐treated group (53.73 ± 4.56%) than in the acellular graft (46.37 ± 5.68%) and fibrin glue groups (45.78 ± 7.14%) but lower than in the autograft group (62.54 ± 8.25%) (P < 0.05). Image analysis on histological observation revealed axonal diameter, axon number, and myelin thickness better with NGF‐treated acellular grafting than with acellular grafting alone and acellular grafting with fibrin glue (P < 0.05). There were no significant differences between NGF‐treated acellular grafting and autografting. This method of sustained site‐specific delivery of NGF can enhance peripheral nerve regeneration across short nerve gaps repaired with acellular nerve grafts. © 2009 Wiley‐Liss, Inc. Microsurgery, 2009.     

Effects of Functional Electrical Stimulation on Denervated Laryngeal Muscle in a Large Animal Model

Bilateral vocal fold paralysis (BVCP) is a life‐threatening condition that follows injury to the Recurrent Laryngeal nerve (RLn) and denervation of the intrinsic laryngeal musculature. Functional electrical stimulation (FES) enables restoration and control of a wide variety of motor functions impaired by lower motor neuron lesions. Here we evaluate the effects of FES on the sole arytenoid abductor, the posterior cricoarytenoid (PCA) muscle in a large animal model of RLn injury. Ten horses were instrumented with two quadripolar intramuscular electrodes in the left PCA muscle. Following a 12‐week denervation period, the PCA was stimulated using a once‐daily training session for 8 weeks in seven animals. Three animals were used as unstimulated controls. Denervation produced a significant increase in rheobase (P < 0.001). Electrical stimulation produced a 30% increase in fiber diameter in comparison with the unstimulated control group (33.9 ± 2.6 µm FES+, 23.6 ± 4.2 µm FES?, P = 0.04). A trend toward a decrease in the proportion of type 1 (slow) fibers and an increase in type 2a (fast) fibers was also observed. Despite these changes, improvement in PCA function at rest was not observed. These data suggest that electrical stimulation using a relatively conservative set of stimulation parameters can reverse the muscle fiber atrophy produced by complete denervation while avoiding a shift to a slow (type 1) fiber type.     

Fascia and soft tissues innervation in the human hip and their possible role in post-surgical pain

Persistent symptoms, most commonly pain, may remain after otherwise successful hip replacement surgery. Innervation of fascia and soft tissues has become increasingly important in etiopathogenesis of pain, but the relative importance of the various anatomical structures in the hip region is still not known. Innervation of skin, superficial adipose tissue, superficial fascia, deep adipose tissue, deep fascia, muscles, capsule, capsule ligament, ligamentum teres, and tendon in the human hip from 11 patients and 2 cadavers were quantified by staining with anti-S100 antibody for myelin-forming Schwann cells, to obtain the percentage of antibody positivity, density and mean diameter of the nerve fibers. The skin was the most highly innervated (0.73% ± 0.37% of positive area in patients; 0.80% ± 0.28% in cadavers); the tendon was the least innervated (0.07% ± 0.01% in patients, 0.07% ± 0.007% in cadavers). The muscles (vasto-lateral and gluteus medius) were the second most innervated structure according the percentage (0.31% ± 0.13% in living humans, 0.30% ± 0.07% in cadavers), but with only a few nerves, with large diameters (mean diameter 36.4 ± 13.4 µm). Instead, the superficial fasciae showed 0.22% ± 0.06% and 0.26% ± 0.05% of positive areas in living humans and cadavers, respectively. Fasciae were invaded by networks of small nerve fibers, revealing a possible role in pain. The superficial fascia was the second most highly innervated tissue after the skin, with a density of 33.0 ± 2.5/cm², and a mean nerve sizes of 19.1 ± 7.2 µm. Lastly, the capsule turned out to be poorly innervated (0.09%), showing that its removal does not necessarily lead to painful consequences. Statement of clinical significance: Deeper knowledge about the innervation of the soft tissue in the human hip joint will enhance study and understanding of the best surgical procedures to follow during hip arthroplasty to reduce post-operative pain.     

A new anchor electrode design for continuous neuromonitoring of the recurrent laryngeal nerve by vagal nerve stimulations

Purpose  Intraoperative neuromonitoring has the limitation that the recurrent laryngeal nerve (RLN) is still at risk for damage between two stimulations with a handheld bipolar stimulation electrode. The purpose of this study was to establish the vagal anchor electrode for real-time monitoring of the RLN in surgical routine and to be alerted to imminent nerve failure by electromyography (EMG) signal analysis whereby the nerve damage becomes reversible. Patients and methods  This fully implantable electrode has been used in addition to a conventional handheld bipolar stimulation electrode during thyroid surgery on 45 consecutive patients (78 nerves at risk) stratified to low- and high-risk groups. The signal analysis was performed as real-time audio/video feedback by the use of a new multichannel EMG system. Results  No complications were attributable to the use of the anchor electrode. The mean delay to place the anchor electrode was 1.45 min, whereas the mean stimulation time of the vagus nerve was 38 min. Stable and repeatable signals were evocable in all cases with one exception. No permanent RLN paralyses occurred in this study. Conclusions  The vagal anchor electrode is safe and easy to use. It allows continuous neuromonitoring without any threats. The new technique will provide more security, especially during preparation steps on the RLN that are difficult for the surgeon.     

Multi‐Electrode Array for Transcutaneous Lumbar Posterior Root Stimulation

Interest in transcutaneous electrical stimulation of the lumbosacral spinal cord is increasing in human electrophysiological and clinical studies. The stimulation effects on lower limb muscles depend on the depolarization of segmentally organized posterior root afferents and, thus, the rostro‐caudal stimulation site. In previous studies, selective stimulation was achieved by varying the positions of single self‐adhesive electrodes over the thoracolumbar spine. Here, we developed a multi‐electrode surface array consisting of 3 × 8 electrode pads and tested its stimulation‐site specificity. The array was placed longitudinally over the spine covering the T10–L2 vertebrae. Two different hydrogel layer configurations were utilized: a single layer adhered to all electrode pads of the array and a configuration comprised of eight separate strips attached to the three transverse electrode pads of each level. Voltage measurements demonstrated that an effectively focused field distribution along the longitudinal extent of the array was not accomplished when using the single continuous hydrogel layer, and segmental selective stimulation of the posterior root afferents was not possible. The separate strips produced a focused electric field distribution at the rostro‐caudal level of the electrode pads selected for stimulation. This configuration allowed for the preferential elicitation of posterior root‐muscle reflexes in either the L2–L4 innervated quadriceps or the L5–S2 innervated triceps surae muscle groups. Such multi‐electrode array for transcutaneous spinal cord stimulation shall allow for improved control of stimulation conditions in electrophysiological studies and time‐dependent and site‐specific stimulation patterns for neuromodulation applications.     

Restoration of Paralyzed Orbicularis Oculi Muscle Function by Controlled Electrical Current

A canine model of facial nerve paralysis was studied to apply controlled electrical current to the peripherally denervated orbicularis oculi muscle, in the attempt to effectively restore the absent function of this denervated muscle. After unilateral facial nerve neurotmesis was performed in eight dogs, the denervated orbicularis oculi muscles of four dogs were electrically stimulated for 75 postoperative days (40 min/day). Denervated and normal orbicularis oculi muscles were electrophysiologically studied and compared with the Student t test. During the study period, minimum closure of denervated treated orbicularis oculi muscles was evoked with average stimulus strength (80-ms duration) of 1.61 ± 0.22 log mA × ms. not significantly different from that of denervated nontreated or normal orbicularis oculi muscles. From days 10 through 30 only, maximum closure of denervated treated orbicularis oculi muscles was achieved with mean pulse strength (80-ms duration) of 2.37 ± 0.09 log mA × ms, significantly lower (P <. 01) than that evoking the same type of contraction from denervated nontreated muscles (80-ms duration, mean 2.83 ± 0.10 log mA × ms). In addition, denervated treated muscle pulse strength eliciting maximum contraction was not significantly different from that of normal orbicularis oculi muscles during the same period. This finding was not observed, however, from day 40 through the end of the study. This investigation demonstrates (1) the transient reversal of denervation changes of paralyzed orbicularis oculi muscle by daily electrical stimulation, and (2) the feasibility of restoring orbicularis oculi muscle function by controlled electrical current.