Feasibility of a Wireless Implantable Multi-electrode System for High-bandwidth Prosthetic Interfacing: Animal and Cadaver Study.

BACKGROUND: Currently used prosthetic solutions in upper extremity amputation have limited functionality, owing to low information transfer rates of neuromuscular interfacing. Although surgical innovations have expanded the functional potential of the residual limb, available interfaces are inefficacious in translating this potential into improved prosthetic control. There is currently no implantable solution for functional interfacing in extremity amputation which offers long-term stability, high information transfer rates, and is applicable for all levels of limb loss. In this study, we presented a novel neuromuscular implant, the the Myoelectric Implantable Recording Array (MIRA). To our knowledge, it is the first fully implantable system for prosthetic interfacing with a large channel count, comprising 32 intramuscular electrodes. QUESTIONS/PURPOSES: The purpose of this study was to evaluate the MIRA in terms of biocompatibility, functionality, and feasibility of implantation to lay the foundations for clinical application. This was achieved through small- and large-animal studies as well as test surgeries in a human cadaver. METHODS: We evaluated the biocompatibility of the system's intramuscular electromyography (EMG) leads in a rabbit model. Ten leads as well as 10 pieces of a biologically inert control material were implanted into the paravertebral muscles of four animals. After a 3-month implantation, tissue samples were taken and histopathological assessment performed. The probes were scored according to a protocol for the assessment of the foreign body response, with primary endpoints being inflammation score, tissue response score, and capsule thickness in µm. In a second study, chronic functionality of the full system was evaluated in large animals. The MIRA was implanted into the shoulder region of six dogs and three sheep, with intramuscular leads distributed across agonist and antagonist muscles of shoulder flexion. During the observation period, regular EMG measurements were performed. The implants were removed after 5 to 6 months except for one animal, which retained the implant for prolonged observation. Primary endpoints of the large-animal study were mechanical stability, telemetric capability, and EMG signal quality. A final study involved the development of test surgeries in a fresh human cadaver, with the goal to determine feasibility to implant relevant target muscles for prosthetic control at all levels of major upper limb amputation. RESULTS: Evaluation of the foreign body reaction revealed favorable biocompatibility and a low-grade tissue response in the rabbit study. No differences regarding inflammation score (EMG 4.60 ± 0.97 [95% CI 4.00 to 5.20] versus control 4.20 ± 1.48 [95% CI 3.29 to 5.11]; p = 0.51), tissue response score (EMG 4.00 ± 0.82 [95% CI 3.49 to 4.51] versus control 4.00 ± 0.94 [95% CI 3.42 to 4.58]; p > 0.99), or thickness of capsule (EMG 19.00 ± 8.76 µm [95% CI 13.57 to 24.43] versus control 29.00 ± 23.31 µm [95% CI 14.55 to 43.45]; p = 0.29) were found compared with the inert control article (high-density polyethylene) after 3 months of intramuscular implantation. Throughout long-term implantation of the MIRA in large animals, telemetric communication remained unrestricted in all specimens. Further, the implants retained the ability to record and transmit intramuscular EMG data in all animals except for two sheep where the implants became dislocated shortly after implantation. Electrode impedances remained stable and below 5 kΩ. Regarding EMG signal quality, there was little crosstalk between muscles and overall average signal-to-noise ratio was 22.2 ± 6.2 dB. During the test surgeries, we found that it was possible to implant the MIRA at all major amputation levels of the upper limb in a human cadaver (the transradial, transhumeral, and glenohumeral levels). For each level, it was possible to place the central unit in a biomechanically stable environment to provide unhindered telemetry, while reaching the relevant target muscles for prosthetic control. At only the glenohumeral level, it was not possible to reach the teres major and latissimus dorsi muscles, which would require longer lead lengths. CONCLUSION: As assessed in a combination of animal model and cadaver research, the MIRA shows promise for clinical research in patients with limb amputation, where it may be employed for all levels of major upper limb amputation to provide long-term stable intramuscular EMG transmission. CLINICAL RELEVANCE: In our study, the MIRA provided high-bandwidth prosthetic interfacing through intramuscular electrode sites. Its high number of individual EMG channels may be combined with signal decoding algorithms for accessing spinal motor neuron activity after targeted muscle reinnervation, thus providing numerous degrees of freedom. Together with recent innovations in amputation surgery, the MIRA might enable improved control approaches for upper limb amputees, particularly for patients with above-elbow amputation where the mismatch between available control signals and necessary degrees of freedom for prosthetic control is highest.

Functional Electrical Stimulation of the Feline Larynx With a Flexible Ribbon Electrode Array.

OBJECTIVES: Success of laryngeal reanimation through neurorrhaphy has been limited by synkinesis and preoperative muscle atrophy. The objective of this study was to investigate the use of epimysial electrode arrays as a means of delivering electrical stimulation to the posterior cricoarytenoid muscles in order to control laryngeal abduction. METHODS: Ribbon electrode arrays with 4 or 8 electrode contacts were used. Four cats underwent implantation of electrode arrays along the surface of the posterior cricoarytenoid muscles. The glottis was visualized with a 0° telescope while electrodes were stimulated at different amplitudes and pulse-width durations. Recordings of stimulated vocal folds were analyzed, and the degree of vocal fold abduction was measured in order to create recruitment curves for the left and right posterior cricoarytenoid. Recruitment curves from electrode channels within the array were compared. RESULTS: Electrodes oriented along the medial aspect of the posterior cricoarytenoid stimulated graded physiologic degrees of abduction depending on the amplitude of stimulation. Electrodes oriented laterally along the posterior cricoarytenoid stimulated greater degrees of simultaneous adduction with abduction. CONCLUSION: Acute studies of ribbon surface electrode arrays placed onto the posterior cricoarytenoid reproduce graded degrees of abduction necessary for the precise function of respiration and speech.

Implantable multichannel wireless electromyography for prosthesis control.

We have developed a prototype implantable device for recording multiple independent channels of EMG and sending those signals wirelessly to an external receiver. This design records multichannel EMG signals for providing simultaneous multi-axis control of prosthetic limbs. This proof-of-concept study demonstrates benchtop performance of the bioamplifier in dry and soaked in saline configurations, as well as system performance in a short-term in vivo study in six dogs. The amplifier was shown to have an input-referred noise of 2.2 µV(RMS), a common mode rejection ratio greater than 55 dB, and neighboring channel isolation averaging 66 dB. The prototype devices were constructed of an amplifier ASIC along with discrete components for wireless function. These devices were coated in silicone and implanted for at least one week in each dog. EMG recorded from each animal as it walked down a hallway had very low noise and swing/stance phases of gait were clearly shown. This study demonstrates this device design can be used to amplify and transmit muscle signals.

Intravenous electrocardiographic guidance for placement of peripherally inserted central catheters.

BACKGROUND: Correct positioning of peripherally inserted central catheters (PICCs) is essential to avoid complications. We evaluated intravenous electrocardiogram (ECG) recordings during PICC placement to assess the effectiveness of this guidance technique to reduce complications resulting from incorrect catheter placement. METHODS: Six patients undergoing PowerPICC catheter insertion were included in this pilot study. Venography through the PICC was performed to identify the superior vena cava-right atrial (SVC-RA) junction. Unipolar ECG recordings from the catheter stylet measured P-wave changes during PICC insertion. RESULTS: The peak P-wave amplitude was highest at the SVC-RA junction. With catheter insertion into the RA, P-wave amplitude decreased and eventually became negative. With catheter withdrawal into the SVC, P-wave amplitude decreased. CONCLUSIONS: P-wave amplitude was highest when the PICC catheter was in the optimal location at the SVC-RA junction. Intravenous ECG monitoring during PICC insertion seems to be a promising technique to guide catheter positioning.

Field deployable EEG monitor for nerve agent casualties.

Early recognition and aggressive management of seizure activity is important in the treatment of patients with nerve agent exposure. However, these patients can experience non-convulsive seizures that are difficult to identify without EEG monitoring. In this paper, we discuss the development and testing of a low-cost, field-deployable device that records and displays patient EEG trends over time. The device is optimized for early levels of care for military and mass casualty patients until they can be relocated to medical facilities with more comprehensive monitoring. The device also records pulse oximetry and acceleration information, and patient data are available for later analysis and improvement of treatment protocols.

Simultaneous, proportional, multi-axis prosthesis control using multichannel surface EMG.

Most upper limb prosthesis controllers only allow the individual selection and control of single joints of the limb. The main limiting factor for simultaneous multi-joint control is usually the availability of reliable independent control signals that can intuitively be used. In this paper, a novel method is presented for extraction of individual muscle source signals from surface EMG array recordings, based on EMG energy orthonormalization along principle movement vectors. In cases where independently-controllable muscles are present in residual limbs, this method can be used to provide simultaneous, multi-axis, proportional control of prosthetic systems. Initial results are presented for simultaneous control of wrist rotation, wrist flexion/extension, and grip open/close for two intact subjects under both isometric and non-isometric conditions and for one subject with transradial amputation.

Control of skeletal muscle force with currents injected via an intrafascicular, microelectrode array.

In spinal cord injured patients, the reanimation of dysfunctional limbs has been achieved with extrinsic stimulation of skeletal muscle via surface, epimysial, and nerve cuff electrodes. However, these neural interfaces have a number of significant problems that are mitigated by the use of electrodes that are inserted directly into the nerves that innervate targeted muscles. These problems, and their mitigation by one embodiment of an intrafascicular electrode array, the Utah Slanted Electrode Array, are the subject of this paper.

Selective motor unit recruitment via intrafascicular multielectrode stimulation.

Recruitment of force via independent asynchronous firing of large numbers of motor units produces the grace and endurance of physiological motion. We have investigated the possibility of reproducing this physiological recruitment strategy by determining the selectivity of access to large numbers of independent motor units through intrafascicular multielectrode stimulation (IFMS) of the peripheral nerve. A Utah Slanted Electrode Array containing 100, 0.5-1.5 mm-long penetrating electrodes was inserted into the sciatic nerve of a cat, and forces generated by the 3 heads of triceps surea in response to electrical stimulation of the nerve were monitored via force transducers attached to their tendons. We found a mean of 17.4 +/- 4.9 (mean +/- SEM) electrodes selectively excited maximal forces in medial gastrocnemius before exciting another muscle. Among electrodes demonstrating selectivity at threshold, a mean of 7.3 +/- 2.7 electrodes were shown to recruit independent populations of motor units innervating medial gastrocnemius (overlap < 20%). Corresponding numbers of electrodes were reported for lateral gastrocnemius and soleus, as well. We used these stimulation data to emulate physiological recruitment strategies, and found that independent motor unit pool recruitment approximates physiological activation more closely than does intensity-based recruitment or frequency-based recruitment.

Interleaved, multisite electrical stimulation of cat sciatic nerve produces fatigue-resistant, ripple-free motor responses.

We studied the use of physiologically based, multisite, intrafascicular electrical stimulation of the sciatic nerve to achieve ripple-free contractions and sustained, fatigue-resistant forces over a physiological range of forces in cat gastrocnemius muscle. Electrode arrays containing 100, 0.5-1.5-mm-long penetrating microelectrodes were inserted into the sciatic nerves of cats, and forces generated by gastrocnemius muscles in response to stimulation of the nerves were monitored via a force transducer attached to the tendons. In single-electrode stimulation, responses evoked by low-frequency [15 pulses/second, (p/s)] stimulation exhibited greater fatigue resistance than did responses evoked by higher frequency stimulation (30 and 60 p/s), but showed far more ripple within each response. We compared interleaved 15 p/s stimulation of four electrodes (100 micros biphasic pulses, 750-ms pulse trains) that produced a net stimulation frequency of 60 p/s with multielectrode 60 p/s quasi-simultaneous stimulation protocols. Across a broad range of forces (10% to 80% of maximum), responses evoked by multielectrode 15 p/s interleaved stimulation exhibited substantially less fatigue than did responses evoked by 60 p/s quasi-simultaneous stimulation, and less ripple than responses evoked by single-electrode 15 p/s stimulation. The effectiveness of this physiologically based stimulation paradigm encourages its application in the field of motor neuroprosthetics.