Dual-channel Stimulation Research Articles

Obesity-associated alterations in glucose metabolism are reversed by chronic bilateral stimulation of the abdominal vagus nerve

Acute vagal stimulation modifies glucose and insulin metabolism, but the effect of chronic bilateral vagal stimulation is not known. Our aim was to quantify the changes in whole-body and organ-specific insulin sensitivities 12 weeks after permanent, bilateral, vagal stimulation performed at the abdominal level in adult mini-pigs. In 15 adult mini-pigs, stimulating electrodes were placed around the dorsal and ventral vagi using laparoscopy and connected to a dual-channel stimulator placed subcutaneously. Animals were divided into three groups based on stimulation and body weight (i.e., lean nonstimulated, obese nonstimulated, and obese stimulated). Twelve weeks after surgery, glucose uptake and insulin sensitivity were measured using positron emission tomography during an isoglycemic clamp. Mean whole-body insulin sensitivity was lower by 34% (P < 0.01) and the hepatic glucose uptake rate was lower by 33% (P < 0.01) in obese-nonstimulated mini-pigs but was no different in obese-stimulated compared with lean mini-pigs. An improvement in skeletal glucose uptake rate was also observed in obese-stimulated compared with obese-nonstimulated groups (P < 0.01). Vagal stimulation was associated with increased glucose metabolism in the cingulate and prefrontal brain areas. We conclude that chronic vagal stimulation improves insulin sensitivity substantially in diet-induced obesity by both peripheral and central mechanisms.

Obesity-Associated Alterations in Glucose Metabolism Are Reversed by Chronic Bilateral Stimulation of the Abdominal Vagus Nerve.

Acute vagal stimulation modifies glucose and insulin metabolism, but the effect of chronic bilateral vagal stimulation is not known. Our aim was to quantify the changes in whole-body and organ-specific insulin sensitivities 12 weeks after permanent, bilateral, vagal stimulation performed at the abdominal level in adult mini-pigs. In 15 adult mini-pigs, stimulating electrodes were placed around the dorsal and ventral vagi using laparoscopy and connected to a dual-channel stimulator placed subcutaneously. Animals were divided into three groups based on stimulation and body weight (i.e., lean nonstimulated, obese nonstimulated, and obese stimulated). Twelve weeks after surgery, glucose uptake and insulin sensitivity were measured using positron emission tomography during an isoglycemic clamp. Mean whole-body insulin sensitivity was lower by 34% (P < 0.01) and the hepatic glucose uptake rate was lower by 33% (P < 0.01) in obese-nonstimulated mini-pigs but was no different in obese-stimulated compared with lean mini-pigs. An improvement in skeletal glucose uptake rate was also observed in obese-stimulated compared with obese-nonstimulated groups (P < 0.01). Vagal stimulation was associated with increased glucose metabolism in the cingulate and prefrontal brain areas. We conclude that chronic vagal stimulation improves insulin sensitivity substantially in diet-induced obesity by both peripheral and central mechanisms.

P84. High-frequency anterior thalamus stimulation interrupts cortical midline theta rhythm during drowsiness in an epileptic patient

Deep brain stimulation (DBS) of anterior thalamic nuclei (ANT) reduces frequency and intensity of epileptic partial and secondarily-generalized seizures. However, exact mechanisms of action and the effects of ANT-DBS on cortical activity are unknown. Recently, we demonstrated in one of our patients who had non-lesional epilepsy the correlation of ANT-DBS with bilateral frontal epileptic patterns ( Bucurenciu et al., 2014 ). We report the case of a 27-years old male epileptic patient with dyscognitive focal seizures, due to a left-hemispheric inoperable lesion, interpreted as focal cortical dysplasia and polymicrogyria, comprising the upper temporal lobe, the insula and the entire parietal lobe. At the age of 25, quadripolar DBS-electrodes (Model 3389, Medtronic®, Minneapolis, MN, USA), connected to a subclavicular dual-channel programmable stimulation device (Activa PC, Medtronic®), were stereotactically implanted in both ANTs. The stimulation parameters were 5 V and 5.5 V, 180 Hz, 150 μ s pulse width, cycling mode with 1min on/3min off. Stimulation on-phases were identified based on periodical reduction of QRS-complex-amplitudes in electrocardiograms. A 20% reduction of seizure frequencies with no side effects were reported after initiation of ANT-DBS. In several long-term EEGs of the patient, prominent non-specific midline-theta frontal rhythms of uncertain significance were observed during drowsiness. During bilateral stimulation via the most upper (superior-lateral) electrode-contacts (3 and 11) a reliable interruption of midline-theta rhythm was observed in EEGs, density-spectral-arrays and power-spectra, similarly to the effect of activating the patient. When the lowest (inferio-medial) electrode contacts (0 and 8) were used for stimulation the midline-theta rhythm was less affected. Other cortical rhythms, such as occipital-alpha or sleep-spindles, were only unspecifically reduced in amplitude by stimulation of both the most upper and the lowest contact-pairs, respectively. The contact-specificity and the selective inhibition of midline-theta rhythm, associated with changes of the power-spectra shape, prove that the observed EEG-amplitude reduction during stimulation is a real desynchronization of midline-theta rhythm and not an artefact. This is the first direct proof of an acute, electrode-contact specific influence of high-frequency ANT-DBS with standard stimulation-parameters on a cortical rhythm and might be relevant for epilepsies involving frontal cortical regions.

Effects of Dual-Channel Functional Electrical Stimulation on Gait Performance in Patients with Hemiparesis

The study objective was to assess the effect of functional electrical stimulation (FES) applied to the peroneal nerve and thigh muscles on gait performance in subjects with hemiparesis. Participants were 45 subjects (age 57.8 ± 14.8 years) with hemiparesis (5.37 ± 5.43 years since diagnosis) demonstrating a foot-drop and impaired knee control. Thigh stimulation was applied either to the quadriceps or hamstrings muscles, depending on the dysfunction most affecting gait. Gait was assessed during a two-minute walk test with/without stimulation and with peroneal stimulation alone. A second assessment was conducted after six weeks of daily use. The addition of thigh muscles stimulation to peroneal stimulation significantly enhanced gait velocity measures at the initial and second evaluation. Gait symmetry was enhanced by the dual-channel stimulation only at the initial evaluation, and single-limb stance percentage only at the second assessment. For example, after six weeks, the two-minute gait speed with peroneal stimulation and with the dual channel was 0.66 ± 0.30 m/sec and 0.70 ± 0.31 m/sec, respectively (P < 0.0001). In conclusion, dual-channel FES may enhance gait performance in subjects with hemiparesis more than peroneal FES alone.

Evaluation of sensation evoked by electrocutaneous stimulation on forearm in nondisabled subjects

Few studies are available in the literature on the sensations artificially created by dual-channel electrocutaneous stimulation. This study assessed the effect of a set of selected stimulation parameters on the sensations evoked by single- or dual-channel electrocutaneous stimulation. The investigated parameters included the stimulation site, the number of pulses, the number of stimulating channels (single- vs dual-channel), and the interleaved time between two channels. The modality, quality, location, and magnitude of the sensations were evaluated when the stimulations were applied on the forearm skin in 16 nondisabled subjects. Tactile perception was found to be induced more easily on the median and ulnar aspect than the dorsal and radial aspect of the forearm. Stimulation site significantly affected the magnitude of the sensation (p < 0.01). Dual-channel stimulation significantly increased the sensation magnitude (p < 0.05) only when the two electrodes were positioned closely. Moreover, a higher number of pulses evoked a movement perception more frequently and the interleaved time showed no significant effect on the magnitude of the sensation. The findings are expected to be useful for sensory substitution and augmentation applications. The results may also help improve users' acceptance of hand prostheses.

Temporal pitch percepts elicited by dual-channel stimulation of a cochlear implant.

McKay and McDermott [J. Acoust. Soc. Am. 100, 1081-1092 (1996)] found that when two different amplitude-modulated pulse trains are presented to two channels separated by <1.5 mm, some cochlear implant (CI) listeners perceive the aggregate temporal pattern. The present study attempted to extend this general finding and to test whether dual-electrode stimulation would increase the upper limit of temporal pitch perception in CIs. Six subjects were asked to rank 12 dual-channel stimuli differing in their rate [ranging from 92 to 516 pps (pulses per second) on each individual channel] and in their inter-channel delay (pulses on the two channels being either nearly simultaneous or delayed by half the period). The data showed that, for an electrode separation of 0.75 or 1.1 mm, (a) the perceived pitch was on average slightly higher for the long-delay than for the short-delay stimuli but never matched the pitch corresponding to the aggregate temporal pattern, (b) the upper limit of temporal pitch did not increase using long-delay stimuli, and (c) the pitch differences between short- and long-delay stimuli were largely insensitive to channel order and to electrode configuration. These results suggest that there may be more independence between CI channels than previously thought.

Neuromuscular electrical stimulation of the gluteus medius improves the gait of children with cerebral palsy

Neuromuscular electrical stimulation (NMES) of the gluteus medius muscles using a surface electrode during functional walking training has never been reported as a management option to improve gait in spastic diplegic children. This study was investigates the short and longer term effects of simultaneous continuous NMES of both hip abductors during walking on the temporal-spatial gait characteristics and hip adductor muscle tone in children with spastic diplegia caused by cerebral palsy (CP). Three groups of subjects participated: an experimental group of twenty-one ambulant spastic diplegic children; a CP control group containing ten ambulant spastic diplegic children; and a healthy control group with twenty normal children. The experimental group received three different NMES management programs. The first NMES program was designed to evaluate the immediate short-term effects of simultaneous continuous NMES of both gluteus medius muscles during walking. The second NMES program aimed to evaluate the effect of 15 minutes of simultaneous and continuous NMES of both gluteus medius muscles during walking, three sessions a day for a week. The third program was similar to the first and was designed to detect any additional changes in gait after full adaptation to NMES and completion of the second program. A dual channel stimulator with self-adhesive electrodes at the tolerable motor threshold level was used with a frequency of 20 Hz and pulse width of 50 micros. The effect of NMES programs was assessed using a three-dimensional gait analysis system and the Modified Ashworth Scale. Significant improvement in the temporal-spatial parameters and hip adductor muscle tone of the experimental group (p < 0.001-0.05) was observed. The NMES management programs used in this study improved the gait of spastic diplegic CP children.

A programmable and portable NMES device for drop foot correction and blood flow assist applications

The Duo-STIM, a new, programmable and portable neuromuscular stimulation system for drop foot correction and blood flow assist applications is presented. The system consists of a programmer unit and a portable, programmable stimulator unit. The portable stimulator features fully programmable, sensor-controlled, constant-voltage, dual-channel stimulation and accommodates a range of customized stimulation profiles. Trapezoidal and free-form adaptive stimulation intensity envelope algorithms are provided for drop foot correction applications, while time dependent and activity dependent algorithms are provided for blood flow assist applications. A variety of sensor types can be used with the portable unit, including force sensitive resistor-based foot switches and MEMS-based accelerometer and gyroscope devices. The paper provides a detailed description of the hardware and block-level system design for both units. The programming and operating procedures for the system are also presented. Finally, functional bench test results for the system are presented.

Site alternatif d’implantation du boîtier de neurostimulation cordonale postérieure

Neurostimulation is now a well-accepted treatment for neuropathic pain. The system is composed of an electrode and a battery-powered stimulator generally implanted in the abdominal wall or subclavicular space according to the location of electrodes. One of the complaints of the patients is the discomfort due to the site and the volume of the battery, particularly with the largest model used for dual channel stimulation. To reduce the frequency of this discomfort we propose an alternative site of implantation of the generator. From January 2001 to February 2002, 17 of our patients chose the buttock area for implantation of the generator. After introduction of the electrodes in the epidural space and tunnelisation has been made to buttock, a pocket is performed in the subcutaneous area to lodge the generator. Ninety-four percent of our patients were very satisfied with this alternative site. One of the 17 patients complained of pain when he was in a reclining position. Otherwise, this technique enable us to perform simultaneously the implantation of the electrodes and the generator facilitating the surgery.

Dual channel deep brain stimulation system (Kinetra) for Parkinson's disease and essential tremor: a prospective multicentre open label clinical study

Objectives: To evaluate the safety and efficacy of a new dual channel stimulator (Kinetra) in patients with severe Parkinson's disease (PD) or essential tremor (ET). Methods: 111 patients with PD...

Multiple frequency steady-state evoked magnetic field mapping of digit representation in primary somatosensory cortex

Magnetic source imaging of multiple frequency steady-state somatosensory evoked responses was examined using a 151-channel magnetoencephalography (MEG) system and a dual-channel electrical stimulator. Somatotopy of digit representation was studied in healthy subjects and effects of injury-related cortical plasticity in patients with unilateral transections of the median or the ulnar nerve. Dipole source locations exhibited somatotopic order with overlap between neighboring digits. In two of three nerve injury patients evidence for cortical reorganization was found. The location of sources related to digits neighboring deafferented digits was changed and their dipole moments were enlarged by comparsion with the sources related to contralateral homologue control digits. As a basis for magnetic source imaging, the recording of multiple frequency somatosensory steady-state evoked responses may be a viable and time saving alternative to the recording of transient evoked responses.

Quantitative Aspects of the Clinical Performance of Transverse Tripolar Spinal Cord Stimulation

A multicenter study was initiated to evaluate the performance of the transverse tripolar system for spinal cord stimulation. Computer modeling had predicted steering of paresthesia with a dual channel stimulator to be the main benefit of the system. The quantitative analysis presented here includes the results of 484 tests in 30 patients. For each test, paresthesia coverage as a function of voltage levels was stored in a computerized database, including a body map which enabled calculation of the degree of paresthesia coverage of separate body areas, as well as the overlap with the painful areas. The results show that with the transverse tripolar system steering of the paresthesia is possible, although optimal steering requires proper placement of the electrode with respect to the spinal cord. Therefore, with this steering ability as well as a larger therapeutic stimulation window as compared to conventional systems, we expect an increase of the long-term efficacy of spinal cord stimulation. Moreover, in view of the stimulation-induced paresthesia patterns, the system allows selective stimulation of the medial dorsal columns.

Proposed specifications for a lumbar spinal cord electrode array for control of lower extremities in paraplegia.

The goal of the study was to provide specifications for a stimulating electrode array to be implanted in the lumbosacral spinal cord as part of a functional neuromuscular stimulation (FNS) system for control of lower extremity muscles in paralyzed individuals. Dual channel stimulation of the quadriceps activation pool in the feline ventral lumbo-sacral spinal cord was performed to measure electrode interactions and to explore the effect of various stimulation paradigms on muscle fatigue. There was no measurable overlap in the populations of motor neurons activated from two different electrodes for spacings > or = 1 mm with currents below 100 microA. However, a statistically significant increase in the population of activated fibers due to current summation was observed when stimuli > or = 70 microA were simultaneously presented through pairs of electrodes within 3 mm of each other. Fatigue effects were studied with three paradigms: 1) stimuli were delivered through a single electrode, 2) stimuli were delivered through two electrodes with the stimulus to the second electrode presented during the refractory period of fibers stimulated by the first electrode, and 3) stimuli were interleaved between the two electrodes such that the stimulus to one electrode was presented midway between stimuli to the other electrode, and the rate of stimulation through a single electrode was half that used in the first two paradigms. Dual channel refractory and single channel stimulation did not differ from each other in the rate at which the muscle fatigued, in both cases the force decayed to 30% of its initial level within 2 min of the initiation of the stimulation regime, whereas the force with interleaved stimulation was still above the initial force at this time due to strong potentiation. Based on these results and on and activation pool dimensions obtained in an earlier study, preliminary specifications are presented for an electrode array to be implanted in the human spinal cord for functional neuromuscular stimulation.

Reduced fatigue in electrically stimulated muscle using dual channel intrafascicular electrodes with interleaved stimulation.

Pairs of intrafascicular electrodes were implanted within single fascicles of the nerve innervating the gastrocnemius muscle in cats. Measurements were made of fatigue induced in the muscle by single and dual channel tetanic stimulation. The level and rate of fatigue induced by concurrent dual channel stimulation (pulses presented simultaneously to the two electrodes) did not differ significantly from that induced by single channel stimulation. However, a significant reduction in the level and rate of muscle fatigue was found with interleaved dual channel stimulation. The extent of reduction in fatigue was found to be inversely related to the amount of overlap in the axonal populations activated by each of the two electrodes.

Discrimination of Complex Electrical Stimulation Through a Multichannel Intracochlear Implant

A model has been developed to describe the electric fields generated in the inner ear when electrical stimuli are presented through a multichannel implant in the scala tympani of the cochlea. The model relies on the hypothesis that stimuli which excite the largest number of neural elements provide the greatest probability of successful discrimination by the implanted subject. It suggests that the effective stimulus is determined by the linear combination of electrical fields produced by the individual channels, and that excitation takes place in a spatially restricted area of the auditory nerve in the vicinity of the stimulating electrodes. The model was tested by biophysical measurements of the potential developed in the stimulated cochlea, and by a psychophysical study of the ability of a monkey to discriminate complex electrical signals using dual channel stimulation. The experimental findings are in agreement with the computer simulations.

A microcomputer-controlled cardiac stimulator

Detailed investigation of abnormal heart rhythms requires electrical stimulators that can deliver sophisticated sequences of stimuli to the heart under controlled laboratory conditions. A dual-channel stimulator that provides an appropriate hardware interface between a controlling microcomputer and the patient is described. The computer gives the system power and flexibility and, most importantly, provides a suitable user interface. The hardware interface is designed to have an ergonomic division between set-up and run-time tasks. Both software and hardware are discussed, and clinical examples of typical usage of the stimulator are given.

Responses of cochlear nucleus units to electrical stimulation through a cochlear prosthesis: Channel interaction

The responses of 39 single units in the ventral cochlear nucleus of acute anesthetized guinea-pigs were studied with continuous electrical stimuli presented through a dual-channel implant in the scala tympani. Implants had four electrodes placed along the axis of the cochlea with 1 mm separations. With a specific pair (either apical or basal) of stimulating electrodes, about half of the units responded when current was flowing apically, while the rest responded to current in the opposite direction. No obvious relation existed between the effective polarity of the basal and apical pairs of electrodes. Two response types were observed while stimulating through both pairs simultaneously. Seventy-nine percent of the units responded to the sum of the current waveforms presented through the two pairs. Twenty-one percent responded to the difference between the waveforms. Both types of responses were observed for suprathreshold as well as for some intensities of stimulation that alone were subthreshold. The type of response was not dependent on the absolute threshold or threshold difference between the two pairs. For equal peak-intensities of stimuli, two-channel stimulation evoked larger responses than single-channel stimulation, provided the two channels were in their effective polarities. Responses to dual-channel stimulation were consistently larger than the summed responses to the two individual single-channel stimuli. The observed responses to the dual-channel stimulation indicate that the adequate stimulus was determined by the linear combination of fields produced by the individual channels in the vicinity of the stimulating electrodes before the auditory nerve is stimulated, and that excitation takes place in a spatially restricted area of the auditory nerve.

Failure of Transcutaneous Electrical Stimulation to Alleviate Experimental Tourniquet Pain

It has been proposed that transcutaneous electrical nerve stimulation (TENS) acts by stimulation of large nerve fibers which inhibits further propagation of nociceptive input conducted along smaller C-nerve fibers. We evaluated the effectiveness of TENS in alleviation of ischemic pain (C-fiber mediated) experimentally produced by the submaximal-effort tourniquet test. Cutaneous electrodes were placed proximal to the tourniquet and TENS was begun prior to exsanguination of the arm. Time from inflation of the tourniquet to onset of intolerable pain was noted together with a visual analog-derived intensity of pain for 10 subjects studied on three separate occasions. The results showed no statistically significant prolongation in the duration of ischemia tolerated nor reduction in the subjective intensity of pain during either single- or dual-channel stimulation in comparison to control levels.

Standing-up of a healthy subject and a paraplegic patient

The joint torques in hip, knee and ankle were measured during the standing-up of a healthy subject. Force plate and stroboscopic photography were used in the experiment. It has been observed that the time courses of particular joint torques depend on the kind of standing-up. On the basis of these results a standing-up procedure for paraplegic patients was proposed. With the use of electrical stimulation to both paralyzed knee extensors and through use of the arm support, a completely paraplegic patient was able to rise independently from the wheel-chair. The same dual-channel stimulation also provides knee locking during standing of spinal cord injured patients.

A microprocessor-controlled dual-channel stimulator.

A programmable pulsed stimulator, presently applied to cardiac pacing, is described. The salient features are dual-channel current output, each of which can supply up to four pulses as well as a pulse tain, with pulse width and delay entered via keyboard, and front panel display of all pulse parameters simultaneously.