Assessment of the Factors Influencing the Recording Performance of Circumneural Electrodes.

The quality of recorded peripheral nerve signals is decisive for their application in therapies. The electroneurogram can be recorded via implantable circumeural electrodes that are wrapped around the peripheral nerve. The shape and amplitude of the signal recorded by the electrode are influenced by the design and contact configuration of the electrode. In this paper, the impact of the number of contacts, contact size and electrical insulation to the outside is investigated to predict the single fiber action potential based on the measured impedance data.

Kilohertz waveforms optimized to produce closed-state Na+ channel inactivation eliminate onset response in nerve conduction block.

The delivery of kilohertz frequency alternating current (KHFAC) generates rapid, controlled, and reversible conduction block in motor, sensory, and autonomic nerves, but causes transient activation of action potentials at the onset of the blocking current. We implemented a novel engineering optimization approach to design blocking waveforms that eliminated the onset response by moving voltage-gated Na+ channels (VGSCs) to closed-state inactivation (CSI) without first opening. We used computational models and particle swarm optimization (PSO) to design a charge-balanced 10 kHz biphasic current waveform that produced conduction block without onset firing in peripheral axons at specific locations and with specific diameters. The results indicate that it is possible to achieve onset-free KHFAC nerve block by causing CSI of VGSCs. Our novel approach for designing blocking waveforms and the resulting waveform may have utility in clinical applications of conduction block of peripheral nerve hyperactivity, for example in pain and spasticity.

Gunshot Wounds to the Upper Extremity.

Upper extremity gunshot wounds result in notable morbidity for the orthopaedic trauma patient. Critical neurovascular structures are particularly at risk. The fractures are often comminuted and may be associated with a variable degree of soft-tissue injury. The literature lacks consensus regarding antibiotic selection and duration, and indications for surgical débridement. Bullets and/or bullet fragments should be removed in cases of plumbism, intra-articular location, nerve impingement, location within a vessel, and location in a subcutaneous position within the hand and/or wrist. Gunshot fractures generally do not follow common fracture patterns seen in blunt injuries, and the complexity of certain gunshot fractures can often be a challenge for the treating orthopaedic surgeon. Common plate and screw constructs may not adequately stabilize these injuries, and innovative fixation techniques may be required. The treatment for bone defects varies by location and severity of injury, and typically requires staged treatment. Nerve injuries after gunshot wounds are common, but spontaneous nerve recovery is expected in most cases.

A microfabricated nerve-on-a-chip platform for rapid assessment of neural conduction in explanted peripheral nerve fibers.

Peripheral nerves are anisotropic and heterogeneous neural tissues. Their complex physiology restricts realistic in vitro models, and high resolution and selective probing of axonal activity. Here, we present a nerve-on-a-chip platform that enables rapid extracellular recording and axonal tracking of action potentials collected from tens of myelinated fibers. The platform consists of microfabricated stimulation and recording microchannel electrode arrays. First, we identify conduction velocities of action potentials traveling through the microchannel and propose a robust data-sorting algorithm using velocity selective recording. We optimize channel geometry and electrode spacing to enhance the algorithm reliability. Second, we demonstrate selective heat-induced neuro-inhibition of peripheral nerve activity upon local illumination of a conjugated polymer (P3HT) blended with a fullerene derivative (PCBM) coated on the floor of the microchannel. We demonstrate the nerve-on-a-chip platform is a versatile tool to optimize the design of implantable peripheral nerve interfaces and test selective neuromodulation techniques ex vivo.

Comparative assessment of limb function and conduction parameters in peripheral nerves in the course of two forms of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive, incurable, neurodegenerative disease affecting the upper and lower motor neuron, which inevitably leads to the impaired fitness of patients and therefore deterioration of their quality of life. AIM: The aim of the study was a comparative assessment of two forms of ALS in terms of limb function and electrophysiological parameters of peripheral nerves. MATERIALS AND METHODS: 20 persons participated in the study, where 10 suffered from bulbar-onset ALS and 10 had limb-onset ALS. Patients were examined clinically and electrophysiologically three times at three-month intervals. Rene Zazzo's card test and Mira Stambak's line-drawing test as well as the 10-metre walk test were used to assess limb function. The results of electrophysiological conduction in the area of nerves of upper and lower limbs were subjected to statistical analysis, as were the results of tests used to assess limb function. RESULTS: The comparative analysis of the obtained results demonstrated that patients with limb-onset ALS showed significant deterioration of conduction in proximal nerve sections compared to patients with bulbaronset ALS. Clinical reflection of this was impairment of limb function with a tendency for progression of these changes over time. CONCLUSIONS: Progressive impairment of conduction in the area of proximal nerve sections and ventral roots of spinal nerves is reflected by the increasing disability of limbs in patients with ALS. In the course of the disease, patients with limb-onset ALS show both worse nerve conduction and limb function than patients with bulbar-onset ALS.

Fast in silico assessment of physical stress for peripheral nerves.

The level of physical stress rules the adaptative response of peripheral nerves, which is crucial to assess their physiological and pathological states. To this aim, in this work, different computational approaches were presented to model the stress response of in vitro peripheral nerves undergoing longitudinal stretch. More specifically, the effects of geometrical simplifications were studied with respect to the amount of computational time needed to obtain relevant information. Similarly, the variation of compressibility of the peripheral nervous tissue was investigated with respect to the variation of longitudinal stress and transversal stretch variations, and with reference to the computational time needed for simulations. Finally, the effect of small dimensional changes was investigated to better understand whether the variation of time was only due to the amount of nodes or elements. In conclusion, since fast in silico models, able to assess the nerve stress, could be a strategic advantage in case of time constraints or on-line evaluation (e.g., surgical interventions), a synergistic use of these approaches was proposed as a possible strategy to decrease the computational time needed for simulations from minutes to seconds. Graphical Abstract A synergistic approach involving both symmetry and tuning of compressibility allows the computational time to be considerably decreased.

A Preliminary Assessment of the Utility of Large-Caliber Processed Nerve Allografts for the Repair of Upper Extremity Nerve Injuries.

Background: Cabled sensory nerve autografts are the historical gold standard for overcoming gaps in larger diameter nerves as repair utilizing large-diameter autograft risks central graft necrosis. Commercially available processed nerve allograft (PNA) is available in diameters up to 5 mm but represents an acellular 3-dimensional matrix as opposed to viable tissue. The purpose of this study is to specifically evaluate whether similar concerns regarding the use of large-caliber PNA are warranted. Methods: The RANGER Registry is an active database designed to collect injury, repair, safety, and outcomes data for PNAs (Avance® Nerve Graft; AxoGen, Inc, Alachua, Florida) according to an institutional review board-approved protocol. The database was queried for patients presenting with large-caliber nerve allograft repairs in the upper extremity. Identified patients reporting quantitative outcomes with a minimum of 9-month follow-up were included in the data set. Results: The large-caliber PNA subgroup included 13 patients with 15 injuries. The mean ± SD age was 36 ± 22 years. Large-caliber single-stranded repairs included twelve 4- to 5-mm-diameter grafts. Large-caliber cabled repairs included the combined use of 3- to 4-mm and 4- to 5-mm-diameter nerve allografts in 3 repairs. The mean nerve gap was 33 ± 10 mm with a mean follow-up time of 13 months. Available quantitative data reported meaningful recovery of sensory and motor function in 67% and 85% of the repairs, respectively. Conclusion: Although based on a small subset of patients, PNAs of up to 5 mm in diameter appear capable of supporting successful nerve regeneration.

Breastfeeding and motor development: A longitudinal cohort study.

BACKGROUND: While there is a large body of work supporting the importance of early feeding practices on cognitive, immunity, behavioural and mental outcomes, few longitudinal studies have focused on motor development. The relationship between duration of breast feeding and motor development outcomes at 10, 14, and 17years were examined. METHODS: Data were obtained from the Western Australian Pregnancy (Raine) Study. There were 2868 live births recorded and children were examined for motor proficiency at 10 (M=10.54, SD=2.27), 14 (M=14.02, SD=2.33) and 17 (M=16.99, SD=2.97) years using the McCarron Assessment of Neuromuscular Development (MAND). Using linear mixed models, adjusted for covariates known to affect motor development, the influence of predominant breast feeding for <6months and ⩾6months on motor development outcomes was examined. RESULTS: Breast feeding for ⩾6months was positively associated with improved motor development outcomes at 10, 14 and 17yearsof age (p=0.019, ß 1.38) when adjusted for child's sex, maternal age, alcohol intake, family income, hypertensive status, gestational stress and mode of delivery. CONCLUSION: Early life feeding practices have an influence on motor development outcomes into late childhood and adolescence independent of sociodemographic factors.

In vitro assessment of TAT - Ciliary Neurotrophic Factor therapeutic potential for peripheral nerve regeneration.

In regenerative neurobiology, Ciliary Neurotrophic Factor (CNTF) is raising high interest as a multifunctional neurocytokine, playing a key role in the regeneration of injured peripheral nerves. Despite its promising trophic and regulatory activity, its clinical application is limited by the onset of severe side effects, due to the lack of efficient intracellular trafficking after administration. In this study, recombinant CNTF linked to the transactivator transduction domain (TAT) was investigated in vitro and found to be an optimized fusion protein which preserves neurotrophic activity, besides enhancing cellular uptake for therapeutic advantage. Moreover, a compelling protein delivery method was defined, in the future perspective of improving nerve regeneration strategies. Following determination of TAT-CNTF molecular weight and concentration, its specific effect on neural SH-SY5Y and PC12 cultures was assessed. Cell proliferation assay demonstrated that the fusion protein triggers PC12 cell growth within 6h of stimulation. At the same time, the activation of signal transduction pathway and enhancement of cellular trafficking were found to be accomplished in both neural cell lines after specific treatment with TAT-CNTF. Finally, the recombinant growth factor was successfully loaded on oxidized polyvinyl alcohol (PVA) scaffolds, and more efficiently released when polymer oxidation rate increased. Taken together, our results highlight that the TAT domain addiction to the protein sequence preserves CNTF specific neurotrophic activity in vitro, besides improving cellular uptake. Moreover, oxidized PVA could represent an ideal biomaterial for the development of nerve conduits loaded with the fusion protein to be delivered to the site of nerve injury.

Comparison of Neurosensory Assessment Methods in Plastic Surgery.

Sensory assessment of the skin is essential to document the function of the sensory fibers of the tested nerves. The Semmes-Weinstein monofilaments, disk-criminator, electrodiagnostic testing, and Pressure-Specified Sensory Device (PSSD) have been currently used to assess sensory function of peripheral nerves. None of these methods is optimal because of different drawbacks; however, an increasing number of articles, which recognize the reliability of PSSD, have been published during the last decade. In this review, following a short overview on basic physiology and assessment methods of the skin sensory receptors, we compared the sensory assessment methods and summarized the applications of the PSSD in the field of different clinical areas, mainly peripheral neuropathies, breast, and flap surgery.

Assessment on selectivity of multi-contact cuff electrode for recording peripheral nerve signals using Fitzhugh-Nagumo model of nerve excitation.

BACKGROUND: Nerve cuff electrodes provide a safe technique for recording nerve signals. Defining a more realized modeling to investigate the selectivity of a cuff electrode in recording from peripheral nervous system is an interesting field of research. METHODS: A four-contact cuff electrode was modeled to evaluate selective recording from a peripheral nerve. Fitzhugh-Nagumo equations were used to model the electromagnetic fields generated by active nerves and electrodes and the ``selectivity index'' used to quantify the selective property of the cuff electrode. RESULTS: The action potentials amplitude and impulse velocity generated by Fitzhugh-Nagumo model are similar to real-life nerve measurements according to the literature. The electrical field distribution caused by the impulse propagation along a specific nerve was the maximum near the corresponding contact. Also, the selectivity was increased with increasing the distance between the active sources and the number of contacts. CONCLUSION: The results of this research showed that Fitzhugh-Nagumo equations could model the nerve excitation accurately and could be used in computer simulation for studying nervous systems. Also, using these equations indicated that multi-contact cuff electrodes could be used in recording peripheral nerve signals in order to discriminate active fascicles in a nerve bundle.

Neurophysiological assessment of auditory, peripheral nerve, somatosensory, and visual system function after developmental exposure to gasoline, E15, and E85 vapors.

The use of gasolines blended with a range of ethanol concentrations may result in inhalation of vapors containing a variable combination of ethanol with other volatile gasoline constituents. The possibility of exposure and potential interactions between vapor constituents suggests the need to evaluate the possible risks of this complex mixture. Previously we evaluated the effects of developmental exposure to ethanol vapors on neurophysiological measures of sensory function as a component of a larger project evaluating developmental ethanol toxicity. Here we report an evaluation using the same battery of sensory function testing in offspring of pregnant dams exposed during gestation to condensed vapors of gasoline (E0), gasoline blended with 15% ethanol (E15) or gasoline blended with 85% ethanol (E85). Pregnant Long-Evans rats were exposed to target concentrations 0, 3000, 6000, or 9000 ppm total hydrocarbon vapors for 6.5h/day over GD9 - GD20. Sensory evaluations of male offspring began as adults. The electrophysiological testing battery included tests of: peripheral nerve (compound action potentials, nerve conduction velocity [NCV]), somatosensory (cortical and cerebellar evoked potentials), auditory (brainstem auditory evoked responses), and visual functions. Visual function assessment included pattern elicited visual evoked potentials (VEP), VEP contrast sensitivity, dark-adapted (scotopic) electroretinograms (ERGs), light-adapted (photopic) ERGs, and green flicker ERGs. The results included sporadic statistically significant effects, but the observations were not consistently concentration-related and appeared to be statistical Type 1 errors related to multiple dependent measures evaluated. The exposure concentrations were much higher than can be reasonably expected from typical exposures to the general population during refueling or other common exposure situations. Overall the results indicate that gestational exposure of male rats to ethanol/gasoline vapor combinations did not cause detectable changes in peripheral nerve, somatosensory, auditory, or visual function when the offspring were assessed as adults.

Quantitative assessment of the nociceptive withdrawal reflex in healthy, non-medicated experimental sheep.

This study aimed to characterize the nociceptive withdrawal reflex (NWR) and to define the nociceptive threshold in 25 healthy, non-medicated experimental sheep in standing posture. Electrical stimulation of the dorsal lateral digital nerves of the right thoracic and the pelvic limb was performed and surface-electromyography (EMG) from the deltoid (all animals) and the femoral biceps (18 animals) or the peroneus tertius muscles (7 animals) was recorded. The behavioural reaction following each stimulation was scored on a scale from 0 (no reaction) to 5 (strong whole body reaction). A train-of-five 1ms constant-current pulse was used and current intensity was stepwise increased until NWR threshold intensity was reached. The NWR threshold intensity (It) was defined as the minimal stimulus intensity able to evoke a reflex with a minimal Root-Mean-Square amplitude (RMSA) of 20µV, a minimal duration of 10ms and a minimal reaction score of 1 (slight muscle contraction of the stimulated limb) within the time window of 20 to 130ms post-stimulation. Based on this value, further stimulations were performed below (0.9It) and above threshold (1.5It and 2It). The stimulus-response curve was described. Data are reported as medians and interquartile ranges. At the deltoid muscle It was 4.4mA (2.9-5.7) with an RMSA of 62µV (30-102). At the biceps femoris muscle It was 7.0mA (4.0-10.0) with an RMSA of 43µV (34-50) and at the peroneus tertius muscle It was 3.4mA (3.1-4.4) with an RMSA of 38µV (32-46). Above threshold, RMSA was significantly increased at all muscles. Below threshold, RMSA was only significantly smaller than at It for the peroneus tertius muscle but not for the other muscles. Data achieved in this study serve as reference for experimental or clinical applications of the conscious sheep model.

Assessment of motor pathways by magnetic stimulation in human and veterinary medicine.

Magnetic stimulation is a non-invasive and painless technique for studying the motor pathways in medical neurology. A time-varying magnetic field induces an electrical field in conducting objects, such as nervous tissue. The technique can be applied to nerve roots and peripheral nerves or to the motor cortex of the brain in human and veterinary medicine. In this review, the basic principles, applications and risk factors of peripheral nerve and motor cortex stimulation in human and veterinary medicine are discussed.

A composite SWNT-collagen matrix: characterization and preliminary assessment as a conductive peripheral nerve regeneration matrix.

Unique in their structure and function, single-walled carbon nanotubes (SWNTs) have received significant attention due to their potential to create unique conductive materials. For neural applications, these conductive materials hold promise as they may enhance regenerative processes. However, like other nano-scaled biomaterials it is important to have a comprehensive understanding how these materials interact with cell systems and how the biological system responds to their presence. These investigations aim to further our understanding of SWNT-cell interactions by assessing the effect SWNT/collagen hydrogels have on PC12 neuronal-like cells seeded within and (independently) on top of the composite material. Two types of collagen hydrogels were prepared: (1) SWNTs dispersed directly within the collagen (SWNT/COL) and (2) albumin-coated SWNTs prepared using the surfactant 'sodium cholate' to improve dispersion (AL-SWNT/COL) and collagen alone serving as a control (COL). SWNT dispersion was significantly improved when using surfactant-assisted dispersion. The enhanced dispersion resulted in a stiffer, more conductive material with an increased collagen fiber diameter. Short-term cell interactions with PC12 cells and SWNT composites have shown a stimulatory effect on cell proliferation relative to plain collagen controls. In parallel to these results, p53 gene displayed normal expression levels, which indicates the absence of nanoparticle-induced DNA damage. In summary, these mechanically tunable SWNT-collagen scaffolds show the potential for enhanced electrical activity and have shown positive in vitro biocompatibility results offering further evidence that SWNT-based materials have an important role in promoting neuronal regeneration.

Effects of stimulation frequency and pulse duration on fatigue and metabolic cost during a single bout of neuromuscular electrical stimulation.

We have investigated the effects of stimulation frequency and pulse duration on fatigue and energy metabolism in rat gastrocnemius muscle during a single bout of neuromuscular electrical stimulation (NMES). Electrical pulses were delivered at 100 Hz (1-ms pulse duration) and 20 Hz (5-ms pulse duration) for the high (HF) and low (LF) frequency protocols, respectively. As a standardization procedure, the averaged stimulation intensity, the averaged total charge, the initial peak torque, the duty cycle, the contraction duration and the torque-time integral were similar in both protocols. Fatigue was assessed using two testing trains delivered at a frequency of 100 Hz and 20 Hz before and after each protocol. Metabolic changes were investigated in vivo using 31P-magnetic resonance spectroscopy (31P-MRS) and in vitro in freeze-clamped muscles. Both LF and HF NMES protocols induced the same decrease in testing trains and metabolic changes. We conclude that, under carefully controlled and comparable conditions, the use of low stimulation frequency and long pulse duration do not minimize the occurrence of muscle fatigue or affect the corresponding stimulation-induced metabolic changes so that this combination of stimulation parameters would not be adequate in the context of rehabilitation.

Transcardial perfusion versus immersion fixation for assessment of peripheral nerve regeneration.

Accurate assessment of peripheral nerve regeneration requires fixation techniques that preserve tissue in a natural state with minimal artifact. While transcardial perfusion fixation is accepted as the gold standard for tissue fixation, the less cumbersome approach of immersion fixation has been criticized for introducing artifacts in brain tissue. We investigated whether immersion fixation increased artifact compared to perfusion fixation in the rat sciatic nerve. Eighteen Lewis rats were randomized into three groups: glutaraldehyde immersion fixation; glutaraldehyde transcardial perfusion; and paraformaldehyde transcardial perfusion. All animals underwent sciatic nerve transection and repair followed by tissue harvest and fixation at three weeks. Qualitative assessment of neural architecture and histological features was followed by quantitative analysis of nerve regeneration parameters. Outcome measures included quantitative histomorphometry, analysis of axon/myelin ratios, assessment of fiber distributions, and ultrastructural analysis. No qualitative or quantitative differences were observed with immersion fixation when compared to the transcardial perfusion fixation methods. Immersion fixation is a valid method for assessment of peripheral nerve regeneration in a rat model.

Avoiding denervation of rectus abdominis in DIEP flap harvest II: an intraoperative assessment of the nerves to rectus.

BACKGROUND: The deep inferior epigastric artery perforator (DIEP) flap aims to reduce donor-site morbidity by minimizing rectus muscle damage; however, damage to motor nerves during perforator dissection may denervate rectus muscle. Although cadaveric research has demonstrated that individual nerves do not arise from single spinal cord segments and are not distributed segmentally, the functional distribution of individual nerves remains unknown. Using intraoperative nerve stimulation, the current study describes the motor distribution of individual nerves supplying the rectus abdominis, providing a guide to nerve dissection during DIEP flap harvest. METHODS: Twenty rectus abdominis muscles in 17 patients undergoing reconstructive surgery involving rectus abdominis (DIEP, transverse rectus abdominis musculocutaneous, or vertical rectus abdominis musculocutaneous flaps) underwent intraoperative stimulation of nerves innervating the infraumbilical segment of the rectus. Nerve course and extent of rectus muscle contraction were recorded. RESULTS: In each case, three to seven nerves entered the infraumbilical segment of the rectus abdominis. Small nerves (type 1) innervated small longitudinal strips of rectus muscle, rather than transverse strips as previously described. There was significant overlap between adjacent type 1 nerves. In 18 of 20 cases, a single large nerve (type 2) at the level of the arcuate line supplied the entire width and length of rectus muscle. CONCLUSIONS: Nerves innervating the rectus abdominis are at risk during DIEP flap harvest. Small, type 1 nerves have overlapping innervation from adjacent nerves and may be sacrificed without functional detriment. However, large type 2 nerves at the level of the arcuate line innervate the entire width of rectus muscle without adjacent overlap and may contribute to donor-site morbidity if sacrificed.

Assessment of nerve excitability in toxic and metabolic neuropathies.

Measurement of nerve excitability by threshold tracking provides complementary information to conventional nerve conduction studies and may be used to infer the activity of a variety of ion channels, energy-dependent pumps, and ion exchange processes activated during the process of impulse conduction. This review highlights recent clinical excitability studies that have suggested mechanisms for nerve involvement in a range of metabolic and toxic neuropathies. While clinical nerve excitability studies are still in their infancy, and it is too early to know whether they have diagnostic value, there is growing evidence of their utility to provide novel insights into the pathophysiological mechanisms involved in a variety of neuropathic disturbances.