Surface Stimulating Electrodes Research Articles

Non-Invasive Stable Sensory Feedback for Closed-Loop Control of Hand Prosthesis.

The absence of somatotopic sensory feedback limits the function of conventional prosthetic hands. In this study, we integrated a non-invasive sensory feedback system into a commercial Bebionic hand with new customized surface stimulation electrodes. Multiple modalities of tactile and hand aperture sensory information were conveyed to the amputee via the technique of evoked tactile sensation (ETS) elicited at projected finger map (PFM) of residual limb and an additional electrotactile stimulation in the ipsilateral upper arm. A previously developed anti-stimulus artifact module was used to remove the stimulus artifact from surface electromyographic (sEMG) signals, and the filtered sEMG envelops controlled the speed of open/close of the Bebionic hand. The Ag/AgCl surface stimulation electrode in 10-mm diameter was specially designed to fit the restricted PFM areas for stable perception. We evaluated the alternating-current (AC) impedance magnitude of this electrode stimulated over 12 hours. The perceptual and upper thresholds in pulse-width over 200 days at PFM areas were recorded to assess the stability of the non-invasive sensory neural interface. The efficacy of multi-modality feedback for identification of physical properties of objects was also assessed. Results showed that the AC impedance of customized surface stimulation electrode was stable over 12 hours of stimulation. The perceptual and upper thresholds were stable over 200 days. This non-invasive sensory feedback enabled a forearm amputee to identify the compliance and length of grasped objects with an accuracy of 100 %. Results illustrated that the multi-modality sensory feedback system provided stable and sufficient sensory information for perceptual discrimination of physical features of grasped objects. Clinical Relevance- This study demonstrated a promising and novel way to restore stable sensory feedback non-invasively for commercial hand prostheses.

Augmented Transcutaneous Stimulation Using an Injectable Electrode: A Computational Study.

Minimally invasive neuromodulation technologies seek to marry the neural selectivity of implantable devices with the low-cost and non-invasive nature of transcutaneous electrical stimulation (TES). The Injectrode® is a needle-delivered electrode that is injected onto neural structures under image guidance. Power is then transcutaneously delivered to the Injectrode using surface electrodes. The Injectrode serves as a low-impedance conduit to guide current to the deep on-target nerve, reducing activation thresholds by an order of magnitude compared to using only surface stimulation electrodes. To minimize off-target recruitment of cutaneous fibers, the energy transfer efficiency from the surface electrodes to the Injectrode must be optimized. TES energy is transferred to the Injectrode through both capacitive and resistive mechanisms. Electrostatic finite element models generally used in TES research consider only the resistive means of energy transfer by defining tissue conductivities. Here, we present an electroquasistatic model, taking into consideration both the conductivity and permittivity of tissue, to understand transcutaneous power delivery to the Injectrode. The model was validated with measurements taken from (n = 4) swine cadavers. We used the validated model to investigate system and anatomic parameters that influence the coupling efficiency of the Injectrode energy delivery system. Our work suggests the relevance of electroquasistatic models to account for capacitive charge transfer mechanisms when studying TES, particularly when high-frequency voltage components are present, such as those used for voltage-controlled pulses and sinusoidal nerve blocks.

An electrophysiological evaluation method for the ovine facial nerve.

IntroductionLarge-animal models such as sheep for facial nerve regeneration research have not yet been established because of the lack of methods for assessing the electrophysiological function of regenerated nerves. In this study, we developed a percutaneous measurement method for the evoked compound muscle action potential (CMAP) of the facial nerve in sheep.MethodsSix 3-year-old castrated male Corriedale sheep were used in this study. Under general anesthesia, an anatomical exploration was performed to identify the course of the buccal branch of the facial nerve and its innervating muscles on one side, followed by the application of surface stimulating electrodes to the contralateral side of the face along the course of the buccal branch of the facial nerve to obtain CMAP measurements of the nasolabial levator muscle.ResultsPercutaneous CMAP measurements of the nasolabial levator muscle could be obtained in all animals by placing stimulating electrodes 1 cm apart on the line coinciding with the course of the buccal branch of the facial nerve revealed by the preceding anatomical exploration. Mean values for electrophysiological parameters were amplitude 4.7 ± 0.7 mV, duration 2.1 ± 0.6 ms, and latency 3.6 ± 0.4 ms.ConclusionWe have established a percutaneous measurement method for CMAP of the buccal branch of the facial nerve in sheep. This method is expected to be very useful in future studies of facial nerve regeneration for long nerve defects in sheep.

Functional Electrical Stimulation Therapy for Retraining Reaching and Grasping After Spinal Cord Injury and Stroke.

Neurological conditions like hemiplegia following stroke or tetraplegia following spinal cord injury, result in a massive compromise in motor function. Each of the two conditions can leave individuals dependent on caregivers for the rest of their lives. Once medically stable, rehabilitation is the main stay of treatment. This article will address rehabilitation of upper extremity function. It is long known that moving the affected limb is crucial to recovery following any kind of injury. Overtime, it has also been established that just moving the affected extremities does not suffice, and that the movements have to involve patient’s participation, be as close to physiologic movements as possible, and should ideally stimulate the entire neuromuscular circuitry involved in producing the desired movement. For over four decades now, functional electrical stimulation (FES) is being used to either replace or retrain function. The FES therapy discussed in this article has been used to retrain upper extremity function for over 15 years. Published data of pilot studies and randomized control trials show that FES therapy produces significant changes in arm and hand function. There are specific principles of the FES therapy as applied in our studies: (i) stimulation is applied using surface stimulation electrodes, (ii) there is minimum to virtually no pain during application, (iii) each session lasts no more than 45–60 min, (iv) the technology is quite robust and can make up for specificity to a certain extent, and (v) fine motor function like two finger precision grip can be trained (i.e., thumb and index finger tip to tip pinch). The FES therapy protocols can be successfully applied to individuals with paralysis resulting from stroke or spinal cord injury.

Modeling and Characterization of Tissue/Electrode Interface in Capacitive µECoG Glassy Carbon Electrodes

Understanding the chronic immune response of brain tissues to implanted neural electrodes is important from both a patient safety and long-term functionality standpoint. One emerging area of interest is examining the effects of the chronic immune response on the long-term functionality of cortical surface stimulating micro-electrodes. In this study, we use a simulation model to examine the parameters that influence the long-term success of cortical surface stimulating electrodes. Two computational models were developed and solved using finite element analysis; the first investigated the externally-induced electric field distribution in the brain tissues during stimulation and the effect of scar tissue formation on the stimulation thresholds. The second evaluated the potential changes in the pH around the electrode during stimulation. The models were based on in vivo experiments that have previously been conducted using chronically implanted glassy carbon based µECoG arrays.

Electroneurography of the ulnar nerve in dogs

Electroneurography as one of the electrodiagnostic techniques is used to measure the speed of action potential which is propagated down the nerve after stimulation. It gives information about normal functioning of the peripheral nerves. The aim of this study was to evaluate the applicability of a new electroneurographic technique by performing motor nerve conduction velocity measurements in the ulnar nerve with surface stimulating electrodes in healthy dogs, to correlate the obtained data by age, limb length, rectal temperature, and sex; and to compare these results with published findings utilizing needle stimulating electrodes. The study was performed in 24 clinically healthy dogs without anaesthesia. Rectal temperatures and limb lengths were measured in all individuals. There were significant correlations among several indicators (age, rectal temperature, limb length, conduction velocity, latency and duration of compound muscle action potentials). Limb length was found to have a significant effect on the duration of the compound muscle action potential from both stimulation sites (proximal/distal; r = 0.71, r = 0.68, P < 0.01), but there was no effect on the conduction velocity or amplitude of the action potentials. There was no significant difference (P > 0.05) in the measured indicators between males and females, even though females had a higher mean conduction velocity than males. These results prove that conduction velocity measurements in dogs could be performed non-invasively, without a danger of infection or haematomas or complications with anaesthesia, which is more favourable and time-saving for clinical practice, and more comfortable for patients.

Monitoring of intense neuromuscular blockade in a pig model

Intense neuromuscular blockade (NMB) measured by post tetanic count (PTC) was monitored, reversed and verified in this pig model. In a cross-over assessor blinded design six pigs were randomized to either no NMB followed by intense NMB, or intense NMB followed by no NMB. Neuromuscular measurements were performed with acceleromyography [train-of-four (TOF) Watch SX]. In all pigs, the response to TOF nerve stimulation was stable and intense NMB (PTC 0-1) was established with rocuronium 3mg/kg. For reversal, the pigs received sugammadex 20-35mg/kg and returned to TOF-ratio above 0.90 within 2.15min after injection. We established a pig model for monitoring intense NMB with surface stimulation electrodes and acceleromyography. We verified total relaxation of the diaphragm and the abdominal muscles at the PTC 0-1 by suction test and with surface electromyography. This pig model is suitable for studies with experimental abdominal surgery with monitoring of intense NMB, and where relaxation of the diaphragm and the abdominal muscles are required.

Phrenic nerve conduction studies: Technical aspects and normative data

In our clinical work we have occasionally encountered difficulties (e.g., no response, concomitant brachial plexus stimulation) in performing phrenic nerve conduction studies. The aim of this study was to overcome these difficulties and obtain our own set of normative data. In 29 healthy volunteers (15 men), aged 21-65 years, phrenic nerve conduction studies were performed using bipolar surface stimulation electrodes and a standard recording montage. Stimulation just above the clavicle, between the sternal and clavicular heads of the sternocleidomastoid muscles, elicited responses at the lowest stimulation strength, without concomitant brachial plexus stimulation. M-wave amplitude and duration changed with respiration, whereas latency and area did not. The normative limit for M-wave latency was 8.0 ms (upper), for amplitude it was 0.46/0.33 mV (lower: inspiration/expiration), and for area it was 4.4 mVms (lower). We suggest a slight modification of the generally used position for phrenic nerve stimulation, and the use of M-wave latency and area (unaffected by the respiratory cycle) in future phrenic nerve conduction studies.

Functional electrical stimulation for grasping and walking: indications and limitations.

This review describes the state of art in the field of Functional Electrical Stimulation (FES) and its impact on improving grasping and walking functions in acute and chronic Spinal Cord Injured (SCI) patients. It is argued that during the early rehabilitation period the FES systems with surface stimulation electrodes should be used to assist training of hand and leg movements in SCI patients. Our clinical trials have shown that a number of acute SCI patients with impaired walking and grasping functions could improve these functions due to training with an adjustable FES system to the point that they finally did not need the FES system to carry out these tasks. Other acute SCI patients, who did not recover the desired function, were enabled to perform either walking or grasping with the FES assistance. We believe that the subjects who can perform grasping or walking with the help of FES, and still use the neuroprosthesis 6 months after being subjected to the FES training, should consider the FES system as a prosthetic device in Activities of Daily Living (ADL). Despite the significant technical progress achieved in the last 10 to 15 years in the FES field, there is a general consensus that these systems are not sufficiently advanced and that they need further development. The limited acceptance of the FES technology can be in part explained by the fact that it is not completely mature and that the patients still require daily assistance to use the FES systems. Nevertheless the present FES treatments combined with conventional occupational and physical therapy still remain the most promising approach in rehabilitating SCI patients. In this review, advantages and limitations of different FES systems that are used to restore grasping and walking functions are discussed.

Development of an EMG recording device from stimulation electrodes for functional electrical stimulation.

A device that records voluntary EMG from a pair of surface stimulation electrodes has been developed for functional electrical stimulation (FES). The device can apply to a small muscle on which it is difficult to locate both the stimulation electrodes and recording electrodes. The device utilizes photo-MOS relays to disconnect the stimulator when it is not active, to ground the electrodes after delivering the stimulation pulses, and to drop the gain of the EMG amplifier during the stimulus period. The device is able to detect the voluntary EMG of a small muscle from the stimulation electrodes for the EMG-controlled FES system.

Anodal block in F-wave studies

Objective: To determine whether F-wave results differ with the anode proximal or distal to the cathode, ie, if clinical anodal block exists. Design: Prospective study of 30 healthy volunteers undergoing nerve conduction and F-wave studies in one median nerve. A needle cathode electrode was used with a surface anode placed alternately proximal and distal to the cathode. The same electromyographer performed all studies with a Dantec Counterpoint machine. Results: F-wave latencies were essentially unaffected by distal versus proximal positioning. Minimum, maximum, and mean F-wave latencies correlated extremely highly ( r = .973 to .988). For both F-wave and M-response latencies and amplitudes, differences between mean values obtained using the two methods were extremely small and were neither clinically nor statistically significant. The frequency of elicitation of F-waves may ( p < .05) have been slightly (3.5%) lower when the anode was in the distal position. Conclusion: Anodal block is not seen in F-wave studies when using needle electrode stimulations. Reversing the stimulator does not seem to be required. Further study with surface stimulating electrodes is underway to confirm results.

Three-dimensional current density distribution under surface stimulation electrodes

Overflow to non-target tissue during FNS can be reduced by controlling current density distribution under surface stimulating electrodes. A method is introduced for the acquisition of 3-D current density distributions under complex surface stimulating FNS electrode geometries. The method makes use of a phantom model in which a conventional homogeneous model has been improved by adding a layer to simulate skin impedance properties, based on specific FNS parameters. Signal acquisition and processing circuits have been developed to simulate the process by which excitable tissue responds to external stimulation. In addition, a data analysis method has been introduced to allow for the characterisation of stimulation current intensity, electrode geometry and pulse waveform required to achieve target muscle activation, with minimal overflow and to avoid pain or burning. Measurements of integrated differential voltage corresponding to current density distribution acquired under electrodes of various geometries are presented in terms of 3-D attenuation coefficient maps as examples of the applicability of the method.

Neurochemical evidence of functional A10 dopamine terminals innervating the ventromedial axis of the neostriatum: in vitro voltammetric data in rat brain slices

The neostriatum (CPu) and nucleus accumbens (NAc) receive their primary dopamine (DA) afferents from the A9 and A10 cell groups, respectively. Anatomical evidence has, however, shown that some clusters of A10 afferents innervate the medial (periventricular) aspect of the CPu 14. The present study used fast cyclic voltammetry (FCV) at carbon fiber microelectrodes to locate and measure the size of these clusters on the basis of diagnostic differences in DA efflux in A9 and A10 terminal regions. All experiments were conducted in CPu or NAc slices superfused with oxygenated artificial CSF at 32°C. Carbon fibre microelectrodes were placed 80 μm below the slice surface and bipolar stimulating electrodes were located 200 μm away. Except in experiments where the stimulation frequency, pulse width or number of pulses were investigated, DA efflux was evoked using 0.1 ms, 10 mA pulses applied singly (1p) or in 20 pulse trains (20p) at 50 Hz and monitored using FCV. The CPu was first mapped on the basis of the ratio of 20p: 1p DA efflux. The CPu consisted mainly (64%) of low ratio (<3) sites while the NAc core comprised exclusively high ratio (> 6) loci. Population analysis revealed a small percentage (10%) of striatal sites with high (>6) ratios. These high ratio sites matched the reported distribution of A10 afferent clusters, being found almost entirely along the ventromedial axis of the CPu. Individual clusters of high ratio sites (20p: 1p ratios > 6), ‘mapped’ on the basis of evoked 20p DA efflux, were found to be irregular in outline and around 500 μm across. In order to characterise the clusters further, the influence of stimulation frequency, train duration (number of pulses) and pulse width on DA efflux were examined. Peak DA efflux in the clusters and NAc occurred at 50 Hz while the striatal matrix had a flat frequency response. Both clusters and NAc showed a similar dependence of DA efflux on the number of pulses in the stimulus train. In the CPu matrix, DA efflux was less dependent on the number of pulses. In the striatal matrix, increasing the stimulation pulse width enhanced DA efflux on trains more than on single pulses while, in both NAc and striatal clusters, there was no preferential effect on trains. The medial location of these clusters within the CPu more closely matches the anatomical distribution of the A10 afferents of Gerfen et al. 14 than the more evenly dispersed striosomes. The DA efflux characteristics in response to different stimulations (frequency response, train duration and pulse width) are also much closer to those of the A10-innervated NAc than the mainly A9 CPu. The data therefore suggest that the observed clusters correspond to small (ca. 500 μm) groups of A10 DA neurones within a predominantly A9 CPu.

Accelographic Train-of-four at Near-threshold Currents

The authors evaluated train-of-four (TOF) fade, as quantified by accelography, in response to neurostimulation at currents ranging from 10 to 60 mA. This was done to determine the range of currents over which measurements of fade remain consistent. In 31 patients (ASA Physical Status 1,2, and 3), anesthesia was induced with fentanyl, midazolam, and thiopental and was maintained with isoflurane and 66% nitrous oxide in oxygen. Surface stimulating electrodes were placed over the ulnar nerve, and an acceleration transducer was placed on the thumb. Succinylcholine was administered to facilitate tracheal intubation; after neuromuscular recovery, a bolus of vecuronium (0.01-0.05 mg.kg-1) and an infusion (0.25-1.5 micrograms.kg-1.min-1) were administered. After documentation of a stable TOF ratio, accelographic TOF responses were quantified in response to 200-microseconds stimulation at 10, 15, 20, 30, 40, 50, and 60 mA, in random order. A total of 95 data sets were collected at different depths of blockade. The TOF ratios maintained intercurrent consistency (P = not significant by nonparametric repeated measures analysis of variance), except at currents near the fourth-twitch (T4) threshold current. This inconsistency was eliminated by testing at greater than or equal to 10 mA above threshold. TOF ratios obtained at 10 mA above T4 threshold correlated highly with those at 60 mA (Spearman r value = 0.94). The authors conclude that the TOF ratio is consistent over a wide range of stimulating currents and that testing with submaximal currents can be performed reliably at greater than or equal to 10 mA above the T4 threshold.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of twitch transdiaphragmatic pressure: surface versus needle electrode stimulation.

The transdiaphragmatic pressure (Pdi) generated during bilateral supramaximal phrenic nerve stimulation at 1 Hz from surface stimulating electrodes was compared with pressures obtained from needle electrodes inserted under local anaesthesia. Surface electrodes were used to obtain diaphragmatic electromyograms and magnetometers to monitor rib cage and abdominal configuration. Twitch Pdi was recorded at functional residual capacity in three normal subjects. Mean (SD) twitch Pdi in the three subjects during stimulation with surface electrodes was 19.4 (1.8), 22.5 (1.1), and 29.3 (2.2) cm H2O compared with 12.9 (1.5), 17:4 (1.3), and 22.6 (3.0) cm H2O with needle stimulating electrodes. Thus phrenic nerve stimulation with needle electrodes was more complicated and more invasive than stimulation with surface electrodes and resulted in lower transdiaphragmatic pressures.

An evaluation of eight peripheral nerve stimulators for monitoring neuromuscular blockade.

The features of eight commercially available peripheral nerve stimulators were compared with those evolved as ideal for monitoring neuromuscular blockade. The pulse waveforms were satisfactory except for that delivered by the CIG series 80 nerve/muscle stimulator. The error in timing of the stimulation patterns was up to 60% in the Professional Instruments NS-2C compared with 8% or less in the other devices. All of the stimulators had maximum current outputs suitable for monitoring with surface stimulating electrodes. The current delivered by the CIG series 80 nerve/muscle stimulator and the Stimlocator SL1.4 sagged by 21% and 25% respectively during a tetanus. The Digistim III, Bard Biomedical 750 digital and the Professional Instruments NS-2C had accurate digital readouts of delivered current.

Electrical stimulation with Pt electrodes. VII. Dissolution of Pt electrodes during electrical stimulation of the cat cerebral cortex

Procedures are described for determining trace quantities of Pt released into brain tissue directly beneath cortical surface stimulation electrodes. Implanted electrodes (1.1 mm Pt discs) were stimulated for 4.5 h, 9 h and 36 h (4 × 9 h/day) with balanced biphasic pulses (20 μC/cm 2 or 100 μC/cm 2 per phase, 50 Hz), following which tissue 0–2 mm beneath stimulation electrodes and the encapsulating tissue adherent to electrodes was excised and analyzed for Pt. A time-dependent increase in Pt concentration was observed between 4.5 h (4–20 ng Pt/stimulation site) and 9 h (50–339 ng Pt/site) of stimulation at 100 μC/cm 2 with nearly all of the Pt located in the encapsulating tissue associated with the electrodes. Somewhat less Pt was observed in the 36 h samples, and it was almost equally distributed between the encapsulating tissue of the electrodes and the first millimeter depth of underlying brain tissue. Little or no Pt was found at electrode sites receiving 20 μC/cm 2 pulses. Control brain tissue samples as well as samples of blood, CSF and kidney were negative for Pt. The findings indicate that the rate of Pt dissolution gradually decreases during in vivo stimulation, and that dissolved Pt may slowly move away from stimulation sites, possibly by diffusion or fluid exchange.

Suralisneurographie: Vergleichende Untersuchung bei Reizung mit Oberflächen- und Nadelelektroden

In 30 healthy volunteers aged 18-30 (ma 13, fern 17) the suralis nerve conduction velocity, the orthodromic NAP-duration and -amplitude were determined using both surface (SE) and needle (NE) stimulating electrodes (lateral malleolus); unipolar needle recording electrodes (sura), however, were used in all trials. Skin temperature was in between 31 and 34 °C (mean value 32,14 °C); in each case nerve conduction velocity (NCV) was calculated up to 35 °C with 2 m/s per degree of deviation. Both the conduction velocity (SE: 56,78 ± 6,1 m/s, NE: 53,27 ± 4,8 m/s) and the NAP-amplitude (SE: 27,3 μV, NE: 12,21 μV) mean values were significantly higher when stimulating with surface electrodes (SE) than with needle electrodes (NE). The normal mean value of NAP-duration, however, was 1,3 ms using either technique. On the base of a linear regression line sensory nerve conduction velocity values with needle electrodes (NE-SNCV) can be transferred into sensory nerve conduction velocity values with surface electrodes (SE-SNCV) by the following formula: NE-SNCV = 26,57 + 0,47 · SE-SNCV.