Therapeutic effectiveness of electric stimulation of the upper-limb poststroke using implanted microstimulators.

OBJECTIVE: To investigate the therapeutic effect of functional exercise augmented by programmable implanted microstimulators on arm and hand function. DESIGN: Before and after study. SETTING: Implantation was performed in a neurosurgery unit, systems were programmed, and tests were conducted in a university laboratory and subjects exercised at home. PARTICIPANTS: Hemiparetic subjects (N=7) with reduced upper-limb function who were at least 12 months poststroke were recruited from the community. No subjects withdrew. INTERVENTION: Microstimulators were implanted into the arms and forearms to activate elbow, wrist, and finger extension, and thumb abduction. After training and programming of the system, subjects underwent 12 weeks of functional home-based exercise with stimulation. MAIN OUTCOME MEASURES: The primary functional measure was the Action Research Arm Test (ARAT). Impairment measures included upper-limb Fugl-Meyer Assessment (FMA) and tests of motor control (tracking index), spasticity (electromyography stretch index) strength, and active range of motion (AROM). The assessor was not blinded, but scores were validated by an independent blinded observer. RESULTS: All subjects were able to perform functional activities at home by using the system. Compliance was excellent, and there were no serious adverse events. Statistically significant improvements were measured (P<.05) in the tracking index (57.3 degrees(2)+/-48.65 degrees(2)), FMA score (6.3+/-3.59), wrist-extensor strength (5.5+/-4.37 N), and wrist AROM (19.3 degrees +/-18.96 degrees). The mean improvement in ARAT score +/- SD of 4.9+/-7.89 was not statistically significant. CONCLUSIONS: This study has shown the feasibility of a programmable implanted microstimulator system used at home to perform functional exercises and a reduction in impairment after 12 weeks.

Poststroke upper-limb rehabilitation using 5 to 7 inserted microstimulators: implant procedure, safety, and efficacy for restoration of function.

OBJECTIVE: To investigate the feasibility of implanting microstimulators to deliver programmed nerve stimulation for sequenced muscle activation to recover arm-hand functions. DESIGN: By using a minimally invasive procedure and local anesthesia, 5 to 7 microstimulators can be safely and comfortably implanted adjacent to targeted radial nerve branches in the arm and forearm of 7 subjects with poststroke paresis. The microstimulators' position should remain stable with no tissue infection and can be programmed to produce effective personalized functional muscle activity with no discomfort for a preliminary 12-week study. Clinical testing, before and after the study, is reported in the accompanying study. SETTING: Microstimulator implantations in a sterile operating room. PARTICIPANTS: Seven adults, with poststroke hemiparesis of 12 months or more. INTERVENTION: Under local anesthesia, a stimulating probe was inserted to identify radial nerve branches. Microstimulators were inserted by using an introducer and were retrievable for 6 days by attached suture. Each device was powered via a radiofrequency link from 2 external cuff coils connected to a control unit. MAIN OUTCOME MEASURES: To achieve low threshold values at the target sites with minimal implant discomfort. Microstimulators and external equipment were monitored over 12 weeks of exercise. RESULTS: Seven subjects were implanted with 41 microstimulators, 5 to 7 per subject, taking 3.5 to 6 hours. Implantation pain levels were 20% more than anticipated. No infections or microstimulator failures occurred. Mean nerve thresholds ranged between 4.0 to 7.7 microcoulomb/cm(2)/phase over 90 days, indicating that cathodes were within 2 to 4 mm of target sites. In 1 subject, 2 additional microstimulators were inserted. CONCLUSIONS: Microstimulators were safely implanted with no infection or failure. The system was reliable and programmed effectively to perform exercises at home for functional restoration.

Acoustic to electric pitch comparisons in cochlear implant subjects with residual hearing.

The aim of this study was to assess the frequency-position function resulting from electric stimulation of electrodes in cochlear implant subjects with significant residual hearing in their nonimplanted ear. Six cochlear implant users compared the pitch of the auditory sensation produced by stimulation of an intracochlear electrode to the pitch of acoustic pure tones presented to their contralateral nonimplanted ear. Subjects were implanted with different Clarion electrode arrays, designed to lie close to the inner wall of the cochlea. High-resolution radiographs were used to determine the electrode positions in the cochlea. Four out of six subjects presented electrode insertions deeper than 450 degrees . We used a two-interval (one acoustic, one electric), two-alternative forced choice protocol (2I-2AFC), asking the subject to indicate which stimulus sounded the highest in pitch. Pure tones were used as acoustic stimuli. Electric stimuli consisted of trains of biphasic pulses presented at relatively high rates [higher than 700 pulses per second (pps)]. First, all electric stimuli were balanced in loudness across electrodes. Second, acoustic pure tones, chosen to approximate roughly the pitch sensation produced by each electrode, were balanced in loudness to electric stimuli. When electrode insertion lengths were used to describe electrode positions, the pitch sensations produced by electric stimulation were found to be more than two octaves lower than predicted by Greenwood's frequency-position function. When insertion angles were used to describe electrode positions, the pitch sensations were found about one octave lower than the frequency-position function of a normal ear. The difference found between both descriptions is because of the fact that these electrode arrays were designed to lie close to the modiolus. As a consequence, the site of excitation produced at the level of the organ of Corti corresponds to a longer length than the electrode insertion length, which is used in Greenwood's function. Although exact measurements of the round window position as well as the length of the cochlea could explain the remaining one octave difference found when insertion angles were used, physiological phenomena (e.g., stimulation of the spiral ganglion cells) could also create this difference. From these data, analysis filters could be determined in sound coding strategies to match the pitch percepts elicited by electrode stimulation. This step might be of main importance for music perception and for the fitting of bilateral cochlear implants.

Implantable microstimulator: magnetic resonance safety at 1.5 Tesla.

RATIONALE AND OBJECTIVE: Ex vivo testing is necessary to characterize implants to determine if it is safe for the patient to undergo a magnetic resonance imaging (MRI) examination. Therefore, the objective of this study was to evaluate MR safety for an implantable microstimulator in association with a 1.5 Tesla MR system. METHODS: A microstimulator (RF BION, Alfred E. Mann Foundation for Scientific Research, Valencia, CA) was evaluated for magnetic field interactions and MRI-related heating. The functional aspects of this implant were assessed immediately before and after exposure to MRI (15 different pulse sequences). Artifacts were also characterized. RESULTS: Magnetic field interactions exhibited by the microstimulator will not pose a hazard after a suitable postimplantation period has elapsed. Temperature changes will not pose a risk. The function of the microstimulator was unaffected by MRI. Artifacts will only create a problem if the area of interest is in proximity to this implant (largest artifact area: T1-weighted spin echo, 2291 mm2; gradient echo, 3310 mm2). CONCLUSION: The overall findings indicated that it is safe for a patient with the microstimulator to undergo MRI at 1.5 Tesla by following specific safety guidelines described herein.