Katharine H. Polasek

Selective stimulation of the human femoral nerve with a flat interface nerve electrode

In humans, we tested the hypothesis that a flat interface nerve electrode (FINE) placed around the femoral nerve trunk can selectively stimulate each muscle the nerve innervates. In a series of intraoperative trials during routine vascular surgeries, an eight-contact FINE was placed around the femoral nerve between the inguinal ligament and the first nerve branching point. The capability of the FINE to selectively recruit muscles innervated by the femoral nerve was assessed with electromyograms (EMGs) of the twitch responses to electrical stimulation. At least four of the six muscles innervated by the femoral nerve were independently and selectively recruited in all subjects. Of these, at least one muscle was a hip flexor and at least two were knee extensors. Results from the intraoperative experiments were used to estimate the potential for the electrode to restore knee extension and hip flexion through functional electrical stimulation. Normalized EMGs and biomechanical simulations were used to estimate joint moments and functional efficacy. Estimated knee extension moments exceed the threshold required for the sit-to-stand transition.

Human Nerve Stimulation Thresholds and Selectivity Using a Multi-contact Nerve Cuff Electrode

Testing of the recruitment properties and selective activation capabilities of a multi-contact spiral nerve cuff electrode was performed intraoperatively in 21 human subjects. The study was conducted in two phases. An exploratory phase with ten subjects gave a preliminary overview of the data and data collection process and a systematic phase with eleven subjects provided detailed recruitment properties. The mean stimulation threshold of 25 plusmn 17 nC was not significantly different than previous studies in animal models but much lower than muscle electrodes. The selectivity, defined as the percent of total activation of the first muscle recruited before another muscle reached threshold, ranged from 27% to 97% with a mean of 55%. In each case, the muscle that was selectively activated was the first muscle to branch distal to the cuff location. This study serves as a preliminary evaluation of nerve cuff electrodes in humans prior to chronic implant in subjects with high tetraplegia

Stimulation Stability and Selectivity of Chronically Implanted Multicontact Nerve Cuff Electrodes in the Human Upper Extremity

Nine spiral nerve cuff electrodes were implanted in two human subjects for up to three years with no adverse functional effects. The objective of this study was to look at the long term nerve and muscle response to stimulation through nerve cuff electrodes. The nerve conduction velocity remained within the clinically accepted range for the entire testing period. The stimulation thresholds stabilized after approximately 20 weeks. The variability in the activation over time was not different from muscle-based electrodes used in implanted functional electrical stimulation systems. Three electrodes had multiple, independent contacts to evaluate selective recruitment of muscles. A single muscle could be selectively activated from each electrode using single-contact stimulation and the selectivity was increased with the use of field steering techniques. The selectivity after three years was consistent with selectivity measured during the implant surgery. Nerve cuff electrodes are effective for chronic muscle activation and multichannel functional electrical stimulation in humans.

Implanted Neuroprosthesis for Restoring Arm and Hand Function in People With High Level Tetraplegia

OBJECTIVE To develop and apply an implanted neuroprosthesis to restore arm and hand function to individuals with high level tetraplegia. DESIGN Case study. SETTING Clinical research laboratory. PARTICIPANTS Individuals with spinal cord injuries (N=2) at or above the C4 motor level. INTERVENTIONS The individuals were each implanted with 2 stimulators (24 stimulation channels and 4 myoelectric recording channels total). Stimulating electrodes were placed in the shoulder and arm, being, to our knowledge, the first long-term application of spiral nerve cuff electrodes to activate a human limb. Myoelectric recording electrodes were placed in the head and neck areas. MAIN OUTCOME MEASURES Successful installation and operation of the neuroprosthesis and electrode performance, range of motion, grasp strength, joint moments, and performance in activities of daily living. RESULTS The neuroprosthesis system was successfully implanted in both individuals. Spiral nerve cuff electrodes were placed around upper extremity nerves and activated the intended muscles. In both individuals, the neuroprosthesis has functioned properly for at least 2.5 years postimplant. Hand, wrist, forearm, elbow, and shoulder movements were achieved. A mobile arm support was needed to support the mass of the arm during functional activities. One individual was able to perform several activities of daily living with some limitations as a result of spasticity. The second individual was able to partially complete 2 activities of daily living. CONCLUSIONS Functional electrical stimulation is a feasible intervention for restoring arm and hand functions to individuals with high tetraplegia. Forces and movements were generated at the hand, wrist, elbow, and shoulder that allowed the performance of activities of daily living, with some limitations requiring the use of a mobile arm support to assist the stimulated shoulder forces.

Intraoperative evaluation of the spiral nerve cuff electrode on the femoral nerve trunk

Evaluation of the Case Western Reserve University spiral nerve cuff electrode on the femoral nerve trunk was performed intraoperatively in four subjects undergoing femoral-popliteal bypass surgery. The threshold, nerve size and selective activation capabilities of the electrode were examined. The activation thresholds for the first muscle to be recruited were 6.3, 9, 10.6, and 37.4 nC with pulse amplitudes ranging from 0.3 to 1 mA. The femoral nerve was found to have an elliptical cross-section with a major axis average length of 9 mm (8-12 mm) and a minor axis length of 1.5 mm. In all four subjects selective activation of the sartorius was obtained. In two subjects, the rectus femoris could also be selectively activated and in one subject the vastus medialis was selectively activated. Each electrode had four independent contacts that were evaluated separately. Small air bubbles were formed in the space over some contacts, preventing stimulation. This occurred in one contact in each electrode, leaving three effective stimulation channels. This issue has been corrected for future studies.

Development of a neuroprosthesis for restoring arm and hand function via functional electrical stimulation following high cervical spinal cord injury

This paper describes the development of an implanted neuroprosthesis for restoring hand and arm function to individuals with high level tetraplegia resulting from C1-C4 spinal cord injury. These individuals have complete paralysis below the level of the neck and are thus highly disabled. The neuroprosthesis under development will restore basic upper extremity movements needed for simple yet important daily activities such as eating and grooming. Simulations performed with a musculoskeletal model of the shoulder and elbow indicate that existing stimulation technology using a realistic number of stimulation channels should be sufficient for providing these functions. The neuroprosthesis will utilize 24 channels of stimulation, muscle-based electrodes for stimulation of hand muscles, and nerve cuff electrodes for stimulation of shoulder and elbow muscles. The two implanted stimulators also include a total of four implanted bipolar EMG recording channels that sample activity in neck and facial muscles. These signals, along with measurements of head orientation, will provide the user command interface for this system

Nerve cuff stimulation and the effect of fascicular organization for hand grasp in nonhuman primates

The overall goal of this work is to introduce nerve cuff electrodes into upper extremity hand grasp systems. The first challenge is to develop a nerve cuff electrode that can selectively activate multiple hand functions from common upper extremity peripheral nerves. The Flat Interface Nerve Electrode (FINE) has shown selective stimulation capability in animal trials. The FINE wraps around the nerve and gently reshapes the nerve and aligns the fascicles within the nerve. Our hypothesis is that the FINE can selectively stimulate multi-fascicular nerves in the human upper extremity resulting in selective hand function. To assess the ability of the FINE to produce control of a hand with many degrees of freedom, we have tested the FINE in nonhuman primates. Fascicular organization and fascicle count are important factors to consider when determining electrode placement. The proximal nerve is an attractive electrode location to access both extrinsic and intrinsic muscles in the upper extremity. A challenge with the nonhuman primate model is that the nonhuman primate median and ulnar nerves both have uni-fascicular regions proximally. The human proximal median and ulnar nerves have an encouraging anatomy of multi-fasciculated nerves with redundant fascicles that may result in more selective hand function than is capable in the nonhuman primate.

Intraoperative Demonstration of Selective Stimulation of the Common Human Femoral Nerve with a FINE

We have tested the hypothesis that the Flat Interface Nerve Electrode (FINE) can selectively stimulate each muscle innervated by the common femoral nerve of the human, near the inguinal ligament in a series of intraoperative trials. During routine vascular surgeries, an 8-contact FINE was placed around the common femoral nerve between the inguinal ligament and the first branching point. The efficacy of the FINE to selectively recruit muscles innervated by the femoral nerve was determined from electromyograms (EMGs) recorded in response to electrical stimulation. At least four of the six muscles innervated by the femoral nerve were selectively recruited in all subjects. Of these, at least one muscle was a hip flexor and two muscles were knee extensors. Results from the intraoperative experiments were used to estimate the potential for the electrode to restore knee extension and hip flexion through Functional Electrical Stimulation (FES). Normalized EMGs and biomechanical simulations were used to estimate joint moments and functional efficacy. Estimated knee extension moments exceed the threshold required for the sit-to-stand transition.

Electrodes for the Neural Interface

Publisher Summary This chapter focuses on the electrodes used as neural interfaces. The neural interface can be unidirectional or bidirectional with information from an engineered system transferred to the neural system and/or information from the neural system transferred to an engineered system. The electrode for the neural interface is a critical component of any neuromodulation system and its development requires careful consideration of all aspects of the neural anatomy, gross physiology, molecular physiology, and electrophysiology. Surface electrodes applied to the skin are widely used in many neuromodulation applications and clinical diagnostic procedures, which ranges from ECG and EEG measurement to transcutaneous electrical nerve stimulation (TENS) for pain management and physical therapy to EMG recording for control of amputee prostheses. Muscle-based electrodes are used in the somatic peripheral nervous system and take advantage of the somatic PNS characteristic of point-like innervations at the neuromuscular junctions. By placing an electrode at a few positions, i.e., at the motor points, of a muscle, the entire muscle can be activated. Peripheral Nervous System Electrodes are designed for implantation directly on the nerves of the peripheral nervous system. The electrode technologies applied to the superficial and distal CNS are similar to the electrodes described for the PNS. These paddle-like electrodes are applied to the dorsal and ventral columns of the spinal cord for stimulation of cough, and respiration function and chronic, and intractable pain. Arrays of the paddle-like discs are embedded in silicon sheeting and applied over the cortical surface for measurement of the cortical activity.

Surface Electrical Stimulation to Evoke Referred Sensation

Surface electrical stimulation (SES) is being investigated as a noninvasive method to evoke natural sensations distal to electrode location. This may improve treatment for phantom limb pain as well as provide an alternative method to deliver sensory feedback. The median and/or ulnar nerves of 35 subjects were stimulated at the elbow using surface electrodes. Strength-duration curves of hand sensation were found for each subject. All subjects experienced sensation in their hand, which was mostly described as a paresthesia-like sensation. The rheobase and chronaxie values were found to be lower for the median nerve than the ulnar nerve, with no significant difference between sexes. Repeated sessions with the same subject resulted in sufficient variability to suggest that recalculating the strength-duration curve for each electrode placement is necessary. Most of the recruitment curves in this study were generated with 28 to 36 data points. To quickly reproduce these curves with limited increase in error, we recommend 10 data points. Future studies will focus on obtaining different sensations using SES with the strength-duration curve defining the threshold of the effective parameter space.