Nerve Cuff Electrode Research Articles

Quantification of recruitment properties of multiple contact cuff electrodes.

Nerve-based stimulating electrodes provide the technology for advancing the function of motor system neural prostheses. The goal of this work was to measure and quantify the recruitment properties of a 12 contact spiral nerve cuff electrode. The cuff was implanted on the cat sciatic nerve trunk, which consists of at least four distinct motor fascicles, and the torque generated at the ankle joint by selective stimulation of the nerve was recorded in nine acute experiments. Comparisons of torques generated with the cuff to torques generated by selective stimulation of individual nerve branches indicated that the cuff allowed selective activation of individual nerve fascicles. Selectivity was dependent on the relative location of the electrode contacts and the nerve fascicles, as well as the size and relative spacing of neighboring fascicles. Selective stimulation of individual nerve fascicles allowed independent and graded control of dorsiflexion and plantarflexion torques in all nine experiments. Field steering currents improved selectivity as reflected by significant increases in the maximum torques that could be generated before spillover to other fascicles, significant increases in the difference between the current amplitude at spillover and the current amplitude at threshold, and significant increases in the slope of the current distance relationship.

Examination of epimysial leads used to stimulate the latissimus dorsi muscle.

Cardiomyoplasty is a new surgical treatment for heart failure in which the patient's latissimus dorsi muscle (LDM) is isolated, wrapped around the heart, and electrically stimulated to provide cardiac assistance. At present, long term stimulation of the LDM is achieved with intramuscular electrodes, which produce minimal nerve damage. This study examined the use of epimysial electrodes by measuring the epimysial lead characteristics during a four-week LDM training. Lead resistance started at 463 +/- 41 omega after implantation, decreased during the following week (251 +/- 16 omega), and remained less than the initial value during the last three weeks (weeks two: 282 +/- 19 omega and week four: 341 +/- 28 omega). The recruitment properties were similar to nervecuff electrodes: low threshold voltages (week one: 0.75 +/- 0.12, week two: 0.90 +/- 0.33, week four: 0.52 +/- 0.10 V) and a very steep recruitment curve with low saturation voltages. Histological examination revealed normal muscle fibers with no inflammatory response. Epimysial leads may be more convenient for most surgeons because the design does not require any free-dissection of the nerve nor guiding a needle around the nerve with the risk of perforating vessels or nerve branches. These results indicate that epimysial leads are worthy of further investigation.

Non-invasive measurement of the input-output properties of peripheral nerve stimulating electrodes

A non-invasive method was developed to determine the input-output ( I O ) properties of peripheral nerve stimulating electrodes. An apparatus was fabricated to measure the 3-dimensional (3-D) isometric torque generated at the cat ankle joint by electrical activation of the sciatic nerve. The performance of the apparatus was quantified, and the utility of the method was demonstrated by measuring the recruitment properties of multiple contact nerve cuff electrodes. Torque-twitch waveforms, recruitment curves of peak torque as a function of stimulus current amplitude, and 2-D joint torque vectors were used to analyze the recruitment properties of the cuff. The peak of the twitch torque was an accurate measure of excitation even for muscles having fibers with varying speeds of contraction. The evoked twitch waveforms and torque vectors generated by selective stimulation of individual nerve branches with a hook electrode were compared to those produced by stimulation of the nerve trunk with the cuff electrode. These data allowed determination of the regions of the nerve trunk were activated by different electrode geometries and stimulus parameters. The positional stability of electrode recruitment properties could be quantified by measuring I O characteristics at different limb positions. The methods described are useful for characterization of neural stimulating electrodes and for studies of motor system physiology.

Soleus forces and soleus force potential during unrestrained cat locomotion

It has been suggested that the soleus muscle in the cat is maximally activated during slow walking (e.g. Walmsley et al.,.Am. J. Physiol. 41, 1203–1216, 1978); however, this opinion is not shared throughout the scientific community (e.g. Hodgson, J. Physiol. 337, 553–562, 1983). Whether or not the soleus is maximally activated for low-demand movements is critical for understanding the interaction and force-sharing of the soleus with the remaining ankle extensor muscles. The purpose of this study was to test experimentally whether the soleus muscle was maximally activated during low-demand, unrestrained movements. In order to achieve this purpose, the soleus was stimulated supramaximally at different instants of the step cycle during walking using a chronically implanted nerve cuff electrode. Forces of the soleus during normal step cycles and during step cycles following supramaximal nerve stimulation were measured using a standard E-shaped tendon force transducer. For slow (0.4 m s −1) and intermediate (0.8 m s −1) speeds of walking, soleus forces could be substantially increased through supramaximal nerve stimulation during the swing and mid-stance phases of the step cycle; for fast walking (1.2 m s −1), such increases in force could be produced only during the swing phase. For all speeds of walking, the soleus forces could not be increased in the early (i.e. from paw contact to about peak force occurrence) or the late (i.e. the last 50–100 ms) parts of the stance phase. Specifically, peak forces and the rate of increase in force immediately following paw contact could not be increased substantially through supramaximal nerve stimulations at the appropriate instant in time for any of the conditions tested here. The results of this study indicate that force production of the soleus is maximal for fast walking (1.2 m s −1) throughout the stance phase, and is maximal for large portions of the stance phase for walking at slow (0.4 m s −1) and intermediate (0.8 m s −1) speeds. These findings have direct implications for explaining the possible mechanism of force-sharing among the cat ankle extensor muscles, and the in vivo mechanical properties of the soleus.

Cuff electrodes for chronic stimulation and recording of peripheral nerve activity

A comparative study of 5 different designs of nerve cuff electrodes was undertaken to determine their relative merits for stimulating and recording whole-nerve activity over extended periods of chronic implantation on large and small peripheral nerves in 8 cats. Four of the designs represent novel fabrication strategies, including 2 based on flexible, thin-film substrates and 2 based on dip-coating silicone elastomer on a cylindrical mandrel. Various advantages and shortcomings of these materials and designs are discussed in the context of the biophysical factors that influence these electrophysiological interfaces, particularly the problem of recording microvolt-level neurograms in the presence of millivolt-level electromyograms from adjacent muscles in freely behaving subjects. The most effective design was one in which a thin sheath of silicone rubber was wrapped around and intra-operatively sealed to a longitudinally slit, tripolar cuff made by dip-coating silicone over stranded stainless steel leads that were prepositioned on a mandrel using polyvinyl alcohol as a temporary adhesive. When properly installed, these electrodes had stable impedances, recruitment thresholds and relatively interference-free recording properties for the duration of this study (up to 9 weeks).

A system for studying the mechanical properties of muscles and the sensorimotor control of muscle forces during unrestrained locomotion in the cat

The purpose of this technical note is to describe an experimental approach that allows the study of mechanical properties of muscles in vitro during normal, unrestrained movements in an animal preparation, and that further allows the investigation of sensorimotor control of joint movements. The preparation contains direct muscle force and EMG measurements of the target muscles (as described previously), and a chronically implanted nerve cuff electrode that may be triggered manually or automatically based on the force output of the targeted muscle. The system has been tested successfully on ankle flexor and extensor muscles of five cats.

Evaluation of a thin-film peripheral nerve cuff electrode.

This is a study of the reaction of large nerves to implantation using a flexible, thin-film cuff electrode. Cuff electrodes were implanted on the sciatic nerve of three cats. An implantation period of six weeks allowed sufficient time for any injury responses in the nerve and connective tissue sheath around the cuff to develop. The electrode came off the nerve in one of the cats. In the remaining two cats, gross observation following explantation of the electrodes revealed encapsulation of the cuffs without swelling of nerve tissue. Histological evaluation did not demonstrate nerve injury. The nerve cuff electrodes, which are comprised of titanium and iridium coatings on a fluorocarbon polymer substrate, appeared unaffected by the implantation, and connective tissue encapsulation did not adhere to either the polymer substrate or metallization. Evaluation of the electrodes using activated iridium oxide charge injection sites in more extended studies is now being undertaken.

Multifunctional properties of ambiguous neurons identified electrophysiologically during vocalization in the awake monkey

1. The nucleus ambiguus (NA) of the medulla contains motoneurons (MNs) for muscles of the larynx, palate, pharynx, and esophagus. Previous studies in anesthetized animals have demonstrated neural discharge correlated closely with respiration, swallowing, and electrical stimulation-elicited vocalization. A preliminary study confirming the above findings was done by recording NA motoneuron extracellular potentials from awake vocalizing monkeys. The present study was undertaken to quantitatively describe discharge properties of a large number of NA neurons recorded from awake, vocalizing monkeys (Macaca nemestrina). 2. In monkeys trained to vocalize for a food reward, extracellular recordings of neurons in and around the nucleus ambiguus were correlated with laryngeal electromyographic activity during vocalization. A nerve cuff electrode on the ipsilateral recurrent laryngeal nerve allowed identification of laryngeal MNs by antidromic activation of laryngeal MNs and the collision test. 3. Most laryngeal MNs became active 100-200 ms before vocalization. They ceased discharging during or immediately after vocalization. Some MNs discharged in close synchrony with bursts of EMG associated with variations in the vocalization. The mean discharge rate of MNs during vocalization was 18 Hz, and the maximum rate in many cells was over 100 Hz. MNs were also active during swallowing. One MN was related only to respiration and one exclusively to swallowing. 4. Some non-motoneurons (Non-MNs) and cells that may possibly be MNs (PossMNs), recorded in and near the NA, showed properties similar to MNs. Many (147) were active only with vocalization, whereas others were active with swallowing (23); respiration (9); vocalization and swallowing (32); vocalization and respiration (40); or vocalization, swallowing, and respiration (17). 5. The present study demonstrates the importance of studying laryngeal MNs in the chronic preparation. Namely, it is shown that both MNs and Non-MNs of the NA are active with more than one activity. Moreover, some Non-MNs are active for only one activity, e.g., vocalization or swallowing. These findings imply the existence of subsets of medullary neurons involved in multiple behaviors for control of generalized laryngeal functions and other subsets related to specific behaviors.

Selective control of muscle activation with a multipolar nerve cuff electrode

Acute experiments were performed on adult cats to study selective activation of medial gastrocnemius, soleus, tibialis anterior, and extensor digitorum longus with a cuff electrode. A spiral nerve cuff containing twelve "dot" electrodes was implanted around the sciatic nerve and evoked muscle twitch forces were recorded in six experiments. Spatially isolated "dot" electrodes in four geometries: monopolar, longitudinal tripolar, tripolar with four common anodes, and two parallel tripoles, were combined with transverse field steering current(s) from an anode(s) located 180 degrees around from the cathode(s) to activate different regions of the nerve trunk. To quantify the degree of selectivity, a selectivity index was defined as the ratio of the force in one muscle to the force in all four muscles in response to a particular stimulus. The selectivity index was used to construct recruitment curves for a muscle with the optimal degree of selectivity. Physiological responses were correlated with the anatomical structure of the sciatic nerve by identifying the nerve fascicles innervating the four muscles, and by determining the relative positions of the electrodes and the nerve fascicles. The results indicated that the use of transverse field steering current improved selectivity. We also found that tripoles with individual dot anodes were more selective than tripoles with four common dot anodes. Stimulation with two parallel tripoles was effective in activating selectively fascicles that could not be activated selectively with only a single tripole. The multipolar cuff proved an effective method to control selectively and progressively the force in muscles innervated by fascicles that were well defined at the level of the cuff.

Comparison of 180-degree and 360-degree skeletal muscle nerve cuff electrodes

Use of skeletal muscle for cardiac augmentation is a promising technique for treatment of end-stage cardiac failure. An electrode woven through the latissimus dorsi that recruits nearby nerve fibers is commonly used to pace skeletal muscles both in clinical practice and in the laboratory. A proximally placed nerve cuff electrode offers potential advantages in improved recruitment of muscle fibers and low threshold for stimulation. We tested the effectiveness of a nerve cuff electrode passed directly about the proximal thoracodorsal nerve. Our report looks at the efficacy of nerve cuff electrode stimulation and compares electrical and histologic characteristics of a 180-degree wrap of the thoracodorsal nerve to a 360-degree wrap in dogs over 3 months. Threshold voltage at the commonly used pulse width of 200 microseconds was typically in the range of 400 to 600 mV for each electrode after 3 months. Statistical analysis revealed no significant difference ( p < 0.05) in threshold voltage or current between the 180-degree and 360-degree nerve cuff electrode either at acute evaluation or after 3 months. Even contraction of latissimus dorsi was achieved with all implants. Adenosine triphosphatase Staining revealed 100% conversion of type II to type I fibers in all stimulated muscles. Histologic examination of the thoracodorsal nerve and latissimus dorsi muscle revealed no abnormalities grossly or by light microscopy. Thus, a carefully applied nerve cuff electrode is an atraumatic, effective method for skeletal muscle stimulation. The 180-degree and 360-degree nerve cuff configurations are equally effective.

Functionally complex muscles of the cat hindlimb

Similarities between the muscle synergies associated with the flexion reflex and locomotion in reduced preparations have suggested that spinal circuits subserving these two motor tasks might share common interneurons. To test this hypothesis in functionally complex muscles, we studied the interaction between low-threshold cutaneous afferents and the locomotor central pattern generator (CPG) during treadmill locomotion in awake, intact cats. Electrical stimuli were delivered via implanted nerve cuff electrodes at all phases of locomotion, and EMGs were recorded from fourteen intramuscular subregions in eight bifunctional thigh muscles (adductor femoris, biceps femoris, caudofemoralis, gracilis, semimembranosus, semitendinosus, tensor fasciae latae, and tenuissimus). In addition, the EMG patterns recorded during locomotion were compared with those recorded during two other centrally driven rhythmical behaviors, scratching and paw shaking, to determine whether the functional relationships among these intramuscular subregions were fixed or task dependent. Four of the five broad, bifunctional muscles studied (biceps femoris, gracilis, semimembranosus, and tensor fasciae latae) had functional subunits that could be differentially activated in one or more of the three movements studied; adductor femoris was consistently uniformly activated despite its distributed skeletal attachments. The pattern of recruitment of the intramuscular functional subunits was movement-specific. The locomotor CPG and cutaneous reflex pathways both similarly subdivided some bifunctional muscles, but not others, into intramuscular subregions. The results of the present study confirm that some combinations of muscle subregions and cutaneous nerves constitute simple reciprocal categories of flexors and extensors, as described originally by Sherrington (1910). "Typical" low threshold excitatory or inhibitory reflex responses were produced in muscles or muscle subregions that were recruited as "net" flexors of extensors, respectively. However, muscles with complex activation patterns during walking often had very individualized, complex reflex responses during locomotion that did not conform to the background locomotion synergies. All of the reflex responses observed were mediated by low threshold cutaneous afferents. These data indicate that there are multiple, low threshold, excitatory and inhibitory cutaneous reflex pathways that have highly specialized connections with flexor and extensor muscles and even their intramuscular subregions. It is also clear that the premotoneuronal circuits mediating these cutaneous reflex effects are not necessarily synonymous with those of the locomotor CPG. These two systems do interact powerfully, however, suggesting some convergence. The nature of the convergence between the CPG and the many independent subsets of spinal interneurons mediating cutaneous reflexes is specialized and muscle subregion-specific.

Upper Extremity Functional Neuromuscular Stimulation

Functional neuromuscular stimulation (FNS) for restoration of upper extremity function has been under development at various centers around the world for over two decades. Application of this technology to date has been primarily focused on selected C4 through C6 level spinal cord injured subjects in whom both palmar and lateral grasp patterns have been restored. Electrical stimulation to individual arm and hand muscles has been provided through surface, percutaneous, epimysial, or nerve cuff electrodes. Various control schemes have been implemented, including detection of shoulder position or head movement, voice activation, respiratory control, and wheelchair mounted switches. Over thirty systems have been implemented in subjects who have used these systems continuously outside the hospital setting for as long as twelve years. Clinical trials employing a common stimulation system are underway at five centers. Further development and research, technology transfer, and expansion of the use of FNS to other...

Joint receptors modulate short and long latency muscle responses in the awake cat

Nerve cuff electrodes were chronically implanted around multiple peripheral nerves in adult cats, including the medial and posterior articular nerves (MAN and PAN) to the knee while EMG electrodes were implanted into seven hindlimb muscles. Randomized load perturbations producing mid-range knee flexions at varying angular velocities were subsequently applied to awake cats. Recordings were initially obtained with knee joint innervation intact and then after local anaesthetic or saline control solution was injected into the knee. Averaged neurogram and EMG responses to the imposed movements were utilized to assess the contribution of joint mechanoreceptor activity to the evoked muscle responses. Additionally, spike-triggered averaging techniques and peri-stimulus time histograms of single joint afferent units isolated from the articular nerve cuffs were utilized to characterize unitary joint receptor responses. The averaged whole nerve response to knee joint perturbations on each of the cuffed articular nerves revealed phasic increases in activity relative to constant background levels. The earliest phasic responses on the articular nerves were initiated at latencies that were too short to be voluntary, occurring in the short latency (reflex) period. Detectable joint receptors were not recruited until after the earliest excitatory responses of agonist/antagonist muscle pairs acting across the knee had occurred, presumably resulting in mechanical loading of the knee joint capsule and subsequent activation of articular mechanoreceptors. Introduction of local anaesthetic into the knee was accompanied by marked diminution in joint afferent activity. Perturbation-evoked muscle responses were characterized by increased activity above background levels in all seven muscles studied, including antagonist muscle pairs. Local anaesthetic-mediated loss of knee joint mechanoreceptor input altered the latency, amplitude and duration of EMG responses in each muscle. The effect of joint anaesthesia in the short latency period was a generalized decrease in all muscle responses relative to normal and saline controls. The loss of afferent input after joint anaesthesia was also associated with altered muscle responses during the long latency period, when both reflex and voluntary mechanisms could potentially contribute to the generation of EMG activity. Interestingly, long latency activity after joint anaesthesia was characterized by "unbalancing" in the EMG responses of some antagonist muscle pairs. This alteration of normal antagonist pair co-contraction patterns served to increase the magnitude of the imposed perturbations, rather than to bring the movements under control. Analysis of single joint afferents isolated from whole joint nerve recordings demonstrated that some joint afferent units were tonically active at quiescent, mid-range knee positions. Additionally, isolated afferents demonstrated different time courses of response to imposed perturbations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animal study of pudendal nerve cuff electrode implants for collision block of motor activity

AbstractThrough previous acute animal studies we have developed an asymmetric two electrode cuff (ATEC) implant for collision block of orthodromic pudendal nerve motor activity. In this paper we describe preliminary results concerning the effectiveness and safety of unilateral pudendal nerve ATECs implanted for 1 month in three adult male dogs. An apparent temporary pressure block of large fiber conduction in the implanted nerve trunks produced distinctive differences between the 2‐week and 4‐week tests in all three animals. In the first two implants significant nerve trunk tissue damage due presumably to surgical trauma and/or cuff encapsulation decreased the effectiveness of ATEC function; however, with the third implant virtually no damage was detected and ATEC effectiveness was high.

Conduction studies in peripheral cat nerve using implanted electrodes: III. The effects of prolonged constriction on the distal nerve segment.

Electrophysiological properties were monitored in detail in chronically constricted peripheral nerves by implanted, multicontact nerve cuff electrodes and correlated with morphometric histology in selected cases. The physiological and histological responses in nerve to a range of constricting cuffs of standard sizes were readily graded. The initial response to any significant constriction was a transient, focal conduction slowing or block at the constriction, followed by more protracted distal effects; the latter ranged from loss of excitability consistent with "dying-back" degeneration to reductions in conduction velocity consistent with histologically observed atrophy. Smaller myelinated fibers tended to have similar but less pronounced changes than larger diameter fibers. Recordings from ventral and dorsal roots showed that distal degeneration was more pronounced in motor than in sensory fibers of similar caliber. Electronmicroscopical measurements showed that basal laminas were relatively preserved around even the most atrophic and demyelinated axons. Perimeter measurements of the basal lamina could be used to estimate the diameter of the original nerve fiber.

Functional electrical stimulation of the latissimus dorsi muscle for use in cardiac assist.

Direct and nondirect nerve stimulation modes of the thoraco-dorsal nerve (TDN) leading to the latissimus dorsi muscle (LDM) were evaluated by using nerve cuff electrodes (NCE) and intramuscular electrodes (IME), respectively. Following electrode implantation, the LDM was chronically stimulated for two months to induce muscle transformation to oxidative, fatigue-resistant type I muscle fibers. Threshold and impedance values were measured regularly to establish the stability of the implants. The LDM was then dissected, shaped into a ventricle, subjected to a hydraulic load and stimulated using a controlled-voltage pulse-train stimulator with adjustable parameters. Electrical input and hydraulic output variables were measured to obtain the recruitment characteristics and to compare the efficiency of the two types of electrodes. Results indicate a tradeoff between the NCE's lower threshold, higher recruitment, and lower energy consumption at saturation, and the IME's greater mechanical stability and better long-term reproducibility.

Electrical Activation of Respiratory Muscles by Methods Other than Phrenic Nerve Cuff Electrodes

Electrical Activation of Respiratory Muscles by Methods Other than Phrenic Nerve Cuff Electrodes

Recruitment data for nerve cuff electrodes: implications for design of implantable stimulators

Recruitment characteristics of nerve cuff electrodes implanted in four cats for five months were measured. Monopolar, bipolar, and tripolar configurations were considered. Approximately twice the current was required to achieve a given response using the tripolar configuration as compared with monopolar stimulation. Bipolar stimulation also required more current than monopolar stimulation. Using the recruitment data, a number of strategies for modulating muscle tension were considered. It was shown that both pulse amplitude and pulse duration should be software-selectable to achieve adequate control of muscle tension when using either pulse amplitude modulation or pulse duration modulation. When using pulse amplitude modulation, it was found to be desirable to operate at a low pulse duration in the high end of the allowable range for pulse amplitude. For pulse duration modulation, one should operate at a low pulse amplitude in the high end of the allowable range for pulse duration. The effect of pulse amplitude and pulse duration step size on the maximum step change in muscle tension and the linearity of the recruitment curves were examined. The use of logarithmic steps in the modulation parameter was examined and was shown to result in improved controllability and linearity.

Method for studying muscle properties under orderly stimulated motor units with tripolar nerve cuff electrode

An electrical nerve stimulation technique, using single tripolar electrode, was shown to be capable of recruiting motor units according to their size, while allowing simultaneous but independent control of firing rate in the active units. Test paradigms consisting of established fundamental physiological concepts of soleus-gastrocnemius architecture, firing rate behaviour of motor units of different sizes, and their susceptibility to fatigue were employed to validate the technique and demonstrate its utility as a basic and applied research tool.

Acute animal studies on electrically induced collision block of pudendal nerve motor activity

AbstractIn this paper we describe acute experiments in five adult male dogs on testing of a pudendal nerve cuff electrode implant for collision block of motor signals to the periurethral sphincter. The average quasi‐trapezoidal stimulus parameters at an “operating point” where antidromic unidirectionally propagating action potentials (needed to produce a motor collision block) were most effectively produced were regulated current level of 14.2 mA (S.D. 2.3 mA), pulse width of 500 μsec (S.D. 71 μsec), and a 90% to 10% exponential fall‐time (following the rectangular stimulus phase) of 840 μsec (S.D. 147 μsec). With these parameters for single monophasic stimuli, an average pressure reduction at the distal urethra of 89% (S.D. 6%) could be elicited in comparison to the maximal single stimulus pressure response. In two tests of collision block with stimulus trains a substantial decrease in distal urethral pressure could be elicited using either monophasic or the electrochemically preferable balanced‐charge biphasic (BCB) waveforms (e.g., pressure reductions of 76% and 89% with 30 Hz BCB collision block).