Implantable Functional Electrical Stimulation Research Articles

The Effect of Implanted Functional Electrical Stimulation on Gait Performance in Stroke Survivors: A Systematic Review.

The emerging literature suggests that implantable functional electrical stimulation may improve gait performance in stroke survivors. However, there is no review providing the possible therapeutic effects of implanted functional electrical stimulation on gait performance in stroke survivors. We performed a web-based, systematic paper search using PubMed, the Cochrane Library, and EMBASE. We limited the search results to human subjects and papers published in peer-reviewed journals in English. We did not restrict demographic or clinical characteristics. We included 10 papers in the current systematic review. Across all included studies, we found preliminary evidence of the potential therapeutic effects of functional electrical stimulation on walking endurance, walking speed, ankle mobility, and push-off force in stroke survivors. However, due to the heterogeneity between the included studies, small sample size, and lack of randomized controlled trials, more studies are critically needed to confirm whether implanted functional electrical stimulation can improve gait performance in stroke survivors.

Significant Impact of Implantable Functional Electrical Stimulation on Gait Parameters: A Kinetic Analysis in Foot Drop Patients

Neurogenic drop foot is a common result of acquired damage of the central nervous system and can cause severe restriction of mobility. ActiGait, an implantable functional electrical stimulation device, restores ankle dorsiflexion by active peroneal nerve stimulation. The aim of our study was to evaluate its effect on foot contact pattern during normal walk. Eight patients with drop foot who used ActiGait in everyday life performed a 20-meter comfortable walk test. Gait parameters were evaluated with an insole system (Medilogic). Percentage of biped stance in a double-step, effective foot length, width of gait, and overall plantar load were measured in comparison with and without activated drop foot stimulation. Effective foot length increased in all patients on average from 46.0% to 60.2% (P= 0.038). However, percentage of biped stance in a double-step showed no significant difference (31.2% vs. 27.8% on average, P= 0.063), nor did width of gait (2.6% vs. 2.4% on average, P= 0.73) and overall plantar load (3.51 N/cm2 vs. 3.39 N/cm2, P= 0.25). The ActiGait implantable drop foot stimulator significantly improves effective foot length during normal walk of patients with neurogenic drop foot. Further investigation is needed to confirm whether ActiGait has no effect on the other parameters or whether it facilitates permanent gait adaptations that persist without the activated device.

Kinematic and kinetic benefits of implantable peroneal nerve stimulation in people with post-stroke drop foot using an ankle-foot orthosis.

Contralesional 'drop foot' after stroke is usually treated with an ankle-foot orthosis (AFO). However, AFOs may hamper ankle motion during stance. Peroneal functional electrical stimulation (FES) is an alternative treatment that provides active dorsiflexion and allows normal ankle motion. Despite this theoretical advantage of FES, the kinematic and kinetic differences between AFO and FES have been scarcely investigated. To test whether walking with implanted FES leads to improvements in stance stability, propulsion, and swing initiation compared to AFO. A 4-channel peroneal nerve stimulator (ActiGait®) was implanted in 22 chronic patients after stroke. Instrumented gait analyses were performed during comfortable walking up to 26 weeks (n = 10) or 52 weeks (n = 12) after FES-system activation. Kinematics of knee and ankle (stance and swing phase) and kinetics (stance phase) of gait were determined, besides spatiotemporal parameters. Finally, we determined whether differences between devices regarding late stance kine(ma)tics correlated with those regarding the swing phase. In mid-stance, knee stability improved as the peak knee extension velocity was lower with FES (β = 18.1°/s, p = 0.007), while peak ankle plantarflexion velocity (β = -29.2°/s, p = 0.006) and peak ankle plantarflexion power (β = -0.2 W/kg, p = 0.018) were higher with FES compared to AFO. With FES, the ground reaction force (GRF) vector at peak ankle power (i.e., 'propulsion') was oriented more anteriorly (β = -1.1°, p = 0.001). Similarly, the horizontal GRF (β = -0.8% body mass, p = 0.003) and gait speed (β = 0.03 m/s, p = 0.015) were higher. An increase in peak ankle plantarflexion velocity and a more forward oriented GRF angle during late stance were moderately associated with an increase in hip flexion velocity during initial swing (rs = 0.502, p = 0.029 and rs = 0.504, p = 0.028, respectively). This study substantiates the evidence that implantable peroneal FES as a treatment for post-stroke drop foot may be superior over AFO in terms of knee stability, ankle plantarflexion power, and propulsion.

A Wireless Implant for Gastrointestinal Motility Disorders.

Implantable functional electrical stimulation (IFES) has demonstrated its effectiveness as an alternative treatment option for diseases incurable pharmaceutically (e.g., retinal prosthesis, cochlear implant, spinal cord implant for pain relief). However, the development of IFES for gastrointestinal (GI) tract modulation is still limited due to the poorly understood GI neural network (gut–brain axis) and the fundamental difference among activating/monitoring smooth muscles, skeletal muscles and neurons. This inevitably imposes different design specifications for GI implants. This paper thus addresses the design requirements for an implant to treat GI dysmotility and presents a miniaturized wireless implant capable of modulating and recording GI motility. This implant incorporates a custom-made system-on-a-chip (SoC) and a heterogeneous system-in-a-package (SiP) for device miniaturization and integration. An in vivo experiment using both rodent and porcine models is further conducted to validate the effectiveness of the implant.

Effects of implantable peroneal nerve stimulation on gait quality, energy expenditure, participation and user satisfaction in patients with post-stroke drop foot using an ankle-foot orthosis.

To investigate whether an implantable functional electrical stimulation (FES) system of the common peroneal nerve (ActiGait®) improves relevant aspects of gait in chronic stroke patients with a drop foot typically using an ankle-foot orthosis (AFO). Ten community-dwelling patients participated, of whom eight patients could be analysed. Gait quality (kinematic, kinetic, and spatiotemporal characteristics) during a 10-meter comfortable walk test, normalised net energy expenditure during a 6-minute walk test, participation (physical activity and stroke impact) and user satisfaction were tested before implantation and at various moments after FES-system activation up to 26 weeks. Walking with FES yielded increased maximum paretic ankle plantarflexion (FES: -0.12; AFO: -4.79°, p < 0.01), higher paretic peak ankle power (FES: 1.46; AFO: 0.98 W/kg, p < 0.05) and better step length symmetry (FES: 14.90; AFO: 21.45% , p < 0.05). User satisfaction was higher for FES, but was unrelated to objective gait improvements. Energy expenditure and participation did not change. Implantable FES improved the use of residual ankle plantarflexion motion, ankle power of the paretic leg and step length symmetry compared to using an AFO, however, not resulting in decreased energy expenditure or improved participation. User satisfaction was highest with FES, but this was not related to the observed gait improvements.

体内埋め込み型機能的電気刺激 (FES) システムにおける伝送誤り訂正回路の有効性

体内埋め込み型機能的電気刺激 (FES) システムにおける伝送誤り訂正回路の有効性

A Biomedical Implantable FES Battery-Powered Micro-Stimulator

The integrated circuit (IC) designs of an implantable functional electrical stimulation (FES) battery-powered micro-stimulator are presented in this paper. The battery is recharged by receiving power magnetically through a coil under supervision of a power management unit. To limit the heat generation on the stimulator when a large magnetic field is present, an on-chip rectifier is capable of limiting the induced voltage and reducing heat generation by providing a low impedance path. The same coil is also used for generating and receiving magnetic fields such that the distances among 16 different stimulator pairs can be estimated simultaneously. To facilitate different clinical applications, a bio-potential sensor is also included. The micro-stimulator can output mono-phasic stimulation current from an 8-bit exponential digital to analog converter (DAC) that has a range between ~2.5 ¿A and ~10 mA. The stimulator communicates with an external master control unit through a 400-MHz wireless link that can support a bit rate of 2.486 MB/s in high speed mode. The total number of stimulators that the communication system can support is 852.

An Integrated Implantable Stimulator That is Fail-Safe Without Off-Chip Blocking-Capacitors

We present a neural stimulator chip with an output stage (electrode driving circuit) that is fail-safe under single-fault conditions without the need for off-chip blocking-capacitors. To miniaturize the stimulator output stage two novel techniques are introduced. The first technique is a new current generator circuit reducing to a single step the translation of the digital input bits into the stimulus current, thus minimizing silicon area and power consumption compared to previous works. The current generator uses voltage-controlled resistors implemented by MOS transistors in the deep triode region. The second technique is a new stimulator output stage circuit with blocking-capacitor safety protection using a high-frequency current-switching (HFCS) technique. Unlike conventional stimulator output stage circuits for implantable functional electrical stimulation (FES) systems which require blocking-capacitors in the microfarad range, our proposed approach allows capacitance reduction to the picofarad range, thus the blocking-capacitors can be integrated on-chip. The prototype four-channel neural stimulator chip was fabricated in XFAB's 1-mum silicon-on-insulator CMOS technology and can operate from a power supply between 5-18 V. The stimulus current is generated by active charging and passive discharging. We obtained recordings of action potentials and a strength-duration curve from the sciatic nerve of a frog with the stimulator chip which demonstrate the HFCS technique. The average power consumption for a typical 1-mA 20-Hz single-channel stimulation using a book electrode, is 200 muW from a 6 V power supply. The silicon area occupation is 0.38 mm(2) per channel.

A microscale photovoltaic neurostimulator for fiber optic delivery of functional electrical stimulation

Recent advances in functional electrical stimulation (FES) show significant promise for restoring voluntary movement in patients with paralysis or other severe motor impairments. Current approaches for implantable FES systems involve multisite stimulation, posing research issues related to their physical size, power and signal delivery, surgical and safety challenges. To explore a different means for delivering the stimulus to a distant muscle nerve site, we have elicited in vitro FES response using a high efficiency microcrystal photovoltaic device as a neurostimulator, integrated with a biocompatible glass optical fiber which forms a lossless, interference-free lightwave conduit for signal and energy transport. As a proof of concept demonstration, a sciatic nerve of a frog is stimulated by the microcrystal device connected to a multimode optical fiber (core diameter of 62.5 µm), which converts optical activation pulses (∼100 µs) from an infrared semiconductor laser source (at 852 nm wavelength) into an FES signal.

Implantable Functional Electrical Stimulation with Inductive Power and Data Transmission System

Functional electrical stimulation (FES) has developed over the last 35 years to become a scientifically, technologically and clinically recognized field of interest in clinical medicine. FES has been applied to locomotion, grasping, ventilation, incontinence, and decubitus healing. However, all of these achievements illustrate the initial applications of FES; its true potential has not yet been realized. Recently, FES systems, which are miniaturized stimulation devices, have been utilized in the clinical setting. However, because the stimulating electrodes of the current FES devices are percutaneous electrodes, which are susceptible to wire breakage, and skin infection an implantable FES stimulating electrode has been introduced in the U.S. and Japan. In the present study, an external power supply method using radio frequency (RF) coupling and data transmission was developed for the control of the implantable FES device. In addition, we review the current understanding of FES devices and their application in clinical medicine.

Implantable FES system for upright mobility and bladder and bowel function for individuals with spinal cord injury

Postintervention. To determine the effectiveness of the Praxis multifunctional implantable functional electrical stimulation (FES) system (Neopraxis Pty. Ltd, Lane Cove, NSW, Australia) to provide standing and stepping ability and bladder and bowel management for individuals with motor complete thoracic level spinal cord injuries (SCI). Pediatric orthopedic hospital specializing in SCI. Three males, ages 17 and 21 years, with motor-complete thoracic level SCI and intact lower motor neurons to the muscles targeted for stimulation. Each subject was successfully implanted with the Praxis FES system. All three subjects received electrodes for upright mobility and the first two subjects received additional electrodes for stimulated bladder and bowel management. Following training, subjects were evaluated in their ability to use FES for nine mobility activities. Acute and chronic experiments of the effect of stimulation on bowel and bladder function were also performed. All three subjects could independently stand up from the wheelchair and could walk at least 6 m using a swing through gait pattern. Two subjects were able to independently perform swing through gait for 6 min and one subject was able to independently ascend and descend stairs. Suppression of reflex bladder contractions by neuromodulation (subject 1) and stimulated contractions of the rectum (subject 2) were observed in acute experiments. When stimulation was applied over the course of several weeks, a positive effect on bowel function was measured. Stimulated bladder contractions were not achieved. The feasibility of using the Praxis FES system for upright mobility and aiding aspects of bladder and bowel function was demonstrated with three subjects with thoracic level SCI.

Reliability of Closed Double Helix Electrode for Functional Electrical Stimulation

The reliability of a closed double helix electrode in the lower limbs was studied. This electrode is an implanted intramuscular electrode and is used for a totally implantable functional electrical stimulation system. Eighty electrodes were evaluated retrospectively with a mean period of 15 months. The total implant time was 1222 electrode months. The cumulative proportion surviving was 0.934 at 6 months, 0.855 at 1 year, 0.765 at 2 years, and 0.730 after 30 months. Fifteen of 80 electrodes failed, seven showed increasing electrode impedance, and eight had undesirable changes in recruitment. Of the failed electrodes, 2/3 failed during the first 10 months. The reliability was 0.91 at 6 months and 0.80 at 1 year after implantation in all muscle groups. The closed double helix electrode displayed an increased reliability when compared with the open double helix electrode at 6 months, and an equivalent reliability as compared with the electrodes developed by Handa and colleagues at 6 months and 1 year, using the chi squared test for independence. This study suggests that the closed double helix electrode has an acceptable reliability and can be used as a part of a totally implantable functional electrical stimulation system.

Pharyngeal Patency Caused by Stimulation of the Hypoglossal Nerve in Anaesthesia-relaxed Patients

Impaired function of the genioglossal muscle is the most frequent reason for upper airway obstruction during sleep. Functional electrical stimulation (FES) of the hypoglossal nerve may be used to push the tongue forward to release the obstruction. Anaesthesia-induced upper airway obstruction resembles the situation during obstructive sleep apnea (OSA) syndrome. In order to develop an implantable FES system for treatment of OSA, we stimulated the exposed hypoglossal nerve in 6 patients undergoing radical cancer surgery of the head and neck region. Tongue movements during stimulation were video filmed and the amount of unobstructed airway achieved with stimulation was estimated using the adjacent intubation tube as reference. In every case, stimulation created an unobstructed airway, larger than the intubation tube.

Signal transmission for implantable medical devices using figure-of-eight coils

A new skin-transparent signal transmission method is proposed. For applications on high energy-consumption medical devices such as total artificial hearts or implantable FES (functional electrical stimulation) systems, we constructed a transcutaneous signal transmission system using figure-of-eight coils, as it is apparent that these applications need feedback and/or controlling signals for stable and safe operation. By employing figure-of-eight coils, we could reduce noise coming from around the coil and still suppress noise emitted from the transmitting coil. In the animal experiment using a goat, we could successfully observe the fluctuation in the amount of the transmitted energy through skin with figure-of-eight coils of 30 mm in diameter. Meanwhile, figure-of-eight coils didn't cause any unfavorable interferences with the electromagnetically driven ventricular assist device connected to the goat's heart at the time.

EMG pattern analysis for patient-responsive control of FES in paraplegics for walker-supported walking.

This paper describes and discusses the employment of EMG pattern analysis to provide upper-motor-neuron paraplegics with patient-responsive control of FES (functional electrical stimulation) for the purpose of walker-supported walking. The system described employs above-lesion surface EMG signals to activate standing and walking functions in a patient-responsive manner. This system has been experimentally applied to paraplegics at Michael Reese Hospital and Medical Center in Chicago since early 1982. Below-lesion response-EMG control from the stimulated sites has been added in 1987 to regulate stimuli levels in the face of fatigue. Although transcutaneous FES alone is being employed, the system is applicable in principle also to implantable FES systems.