Jean-Louis Divoux

Original electronic design to perform epimysial and neural stimulation in paraplegia

This paper presents an original electronic architecture to manage epimysial and neural stimulation using the same implantable device. All the muscles needed to achieve lower limb movements such as standing and walking can thus be activated. Mainly for surgical reasons, some muscles need to be stimulated through different inputs: epimysium or motor nerve. We developed an electronic solution, including the design of an application-specific integrated circuit, to meet the requirements of both types of stimulation. Five years after the successful implantation of the system, we were able to evaluate the systems performance. The patient is still using the system at home and no failure occurred during this 5-year period. We conclude that the electronic design not only provides a unique investigative tool for research, but that it can also be used to restore the motor function of the lower limb. This technology has an advantage over external stimulation because the patient can safely use the system at home. However, improvements such as lower power consumption, and thus greater autonomy, are needed. We further conclude that the modelling of the electrical behaviour of the electrodes is reliable and the estimated parameter values are homogeneous and consistent for the same type of electrode. Thus, the three parameters of the first-order model can be identified from an acute animal experiment and provide a means to optimize the design of the output stage of implanted stimulators.

Development of an implantable transverse intrafascicular multichannel electrode (TIME) system for relieving phantom limb pain

Phantom limb pain frequently follows amputation. Currently there is no fully effective treatment available. Our aim is to develop an innovative Human Machine Interface (HMI) where we apply multi-channel microstimulation to the nerve stump of an amputee subject to manipulate the phantom limb sensations and explore the possibility of using microstimulation as a treatment for phantom limb pain.

Development of a neurotechnological system for relieving phantom limb pain using transverse intrafascicular electrodes (TIME)

Abstract Phantom limb pain (PLP) is a chronic condition that develops in the majority of amputees. The underlying mechanisms are not completely understood, and thus, no treatment is fully effective. Based on recent studies, we hypothesize that electrical stimulation of afferent nerves might alleviate PLP by giving sensory input to the patient if nerve fibers can be activated selectively. The critical component in this scheme is the implantable electrode structure. We present a review of a novel electrode concept to distribute highly selective electrode contacts over the complete cross section of a peripheral nerve to create a distributed activation of small nerve fiber ensembles at the fascicular level, the transverse intrafascicular multichannel nerve electrode (TIME). The acute and chronic implantations in a small animal model exhibited a good surface and structural biocompatibility as well as excellent selectivity. Implantation studies on large animal models that are closer to human nerve size and anatomical complexity have also been conducted. They proved implant stability and the ability to selectively activate nerve fascicles in a limited proximity to the implant. These encouraging results have opened the way forward for human clinical trials in amputees to investigate the effect of selective electrical stimulation on PLP.

Effects of chronic abdominal vagal stimulation of small-diameter neurons on brain metabolism and food intake

BACKGROUND Abdominal bilateral vagal stimulation reduces food intake in animals. However, the classical square wave, mA range current generator is poorly effective to evoke action potentials on A∂ and C neurons that represent the majority of vagal neurons at the abdominal level. OBJECTIVE/HYPOTHESIS METHODS: The current thresholds for pulsons (S2 & S3) and millisecond pulses (S1) required to trigger action potentials were calculated in 5 anaesthetized pigs using single fibre recording. Similar stimulation protocols were compared chronically to sham stimulation in 24 pigs. After two weeks of chronic stimulation, food intake and brain metabolism were investigated. The electrical characteristics and histology of the vagus nerve were also studied. RESULTS S3 stimulation required a lower amount of charges to trigger an action potential. Chronically applied S2 & S3 activated the dorsal vagal complex and increased the metabolism of its afferent cortical structures. They also reduced energy intake together with a reduced ingestion of high fat and high sugar diets. All these effects were not observed for the S1 group. The vagal histology for the S1, S2 and S3 groups was not different from that of the sham. CONCLUSIONS These findings demonstrate that pulsons applied bilaterally on the abdominal vagus reduced food intake as a consequence of the activation of the brainstem and higher-order brain areas.

Advanced 56 Channels Stimulation System to Drive Intrafascicular Electrodes

A wearable, 56-channel stimulator was developed and successfully tested to drive multichannel intrafascicular electrodes. It is able to safely elicit sensory afferent signals through the activation of 4 Time-4H intrafascicular electrodes. The STIMEP embeds not only the pulse generator but also a software that ensures: (i) real time control by a hand-prosthesis, (ii) embedded procedures for sensation mapping interfaced with a PC software, (iii) impedance follow-up, (iv) real-time safety management.

S19.5 Transverse, intrafascicular multi-electrode (TIME) system for induction of sensation and treatment of phantom limb pain in amputees

Methods: Patients with visual field impairments resulting from partial optic nerve damage were randomly assigned to a rtACS (n = 24) or sham (n = 18) group. rtACS (<800mA, 20 40 Hz) or sham was given for 20 40 min/daily for 10-days. Visual fields and QoL (vision-related:National Eye Institute Visual Function Questionnaire VFQ; health-related: Short Form Health Survey SF-36) were collected. Changes in QoL were correlated with changes in primary and secondary visual field outcome measures for both groups. Results: Improvements of detection ability (DA) in the defective visual field (primary outcome measure) were significantly larger after rtACS (41.09±78.91%) then after sham-stimulation (13.59±26.32%; p < 0.05). Also, secondary outcome measures (DA in the whole tested visual field, static and kinetic perimetry) provided further evidence of rtACS efficacy. Significant improvements in NEI-VFQ general vision were observed in both groups and were significantly larger after rtACS (11.30±13.50, Z = 3.21, p < 0.001) than sham (4.17±9.43, Z = 1.73, p < 0.05; between group difference: Z = 1.71, p < 0.05). Correlations between DA change and some NEI-VFQ domains were modest. No significant correlations were observed for DA and SF-36 results. Conclusions: rtACS facilitates vision restoration after unilateral, longterm optic nerve lesion as assessed both by objective DA changes and improvements in some NEI-VFQ subscales. Both were positively and modestly correlated, which suggests that factors other than visual field size also contribute to improved vision-related QoL as induced by rtACS.

Developments towards a Psychophysical Testing Platform - A Computerized Tool to Control, Deliver and Evaluate Electrical Stimulation to Relieve Phantom Limb Pain

Artificially inducing phantom hand sensations by electrical stimulation may reduce PLP. The use of implantable, multi-channel microelectrodes provides the opportunity to selectively activate sensory fibres. However, combinations of variables from a multichannel stimulation system can produce a huge number of possible stimulation paradigms. It makes the use of psychophysical evaluation of the evoked sensations an impractical and time-consuming task in the clinical setting. Our aim is to develop a computerized, automatic, psychophysical testing platform to support control, delivery and evaluation of the electrical stimulation for PLP relief.