Nerve Conduction Block Research Articles

Temporal properties of transcutaneous direct current motor conduction block.

Direct current (DC) electrical block of peripheral nerve conduction shows promise for clinical applications to treat spasticity, pain, and cardiac arrhythmias. Most previous work has used invasive nerve cuffs. Here we investigate the potential of non-invasive transcutaneous direct current motor block (tDCB). 

In anesthetized rats, force output from the tibialis and peroneus muscles was measured in response to stimulation proximally on the sciatic nerve. DC blocking waveforms were delivered via a surface electrode placed distally on the skin over the common peroneal nerve. The efficacy of the block was observed as the reduction/abolition of muscle force. Experiments using this model were performed with two different electrode types. A range of DC amplitudes and durations was used to elucidate the temporal properties of block.

Higher levels of DC resulted in a larger block percentage. The amount of time needed to induce block depended on the level of DC, with smaller amplitudes resulting in longer induction times. When block was applied for a longer period of time (120s), the block was sustained following DC delivery. This "recovery period" was longer for higher amplitudes of block. 

In addition to the block thresholds and temporal effects, two additional evaluations were made: In some animals the efficacy of tDCB to block tetanic muscle contractions was successfully verified. Finally, the effect of tDCB on nerve health was verified using a second distal electrode for comparison. 

In this study, tDCB has been shown to reversibly blocked action potentials in peripheral motor nerves. A lower amplitude applied for a longer duration could produce delayed complete block as well as delayed partial block. Also, a higher amplitude was associated with a longer recovery time. These temporal properties are important considerations for potential clinical applications.&#xD.

Regional nerve block in postoperative analgesia after cesarean section: A narrative review

Of all obstetric operations, cesarean section is one of the most common. The impact of postoperative pain on physical and mental health in women cannot be ignored. Moreover, effective postoperative analgesia is essential in women who have given birth. Traditional systemic analgesic methods (intravenous analgesia, oral analgesics, etc) are often accompanied by adverse reactions that are positively correlated with the drug dosage. Regional nerve block is an analgesic and anesthetic technique that temporarily blocks nerve conduction by injecting local anesthetics around the nerve roots, nerve trunks, nerve plexus, ganglia, or surgical area, thereby alleviating or eliminating pain. Currently, the regional block techniques used for postoperative analgesia following cesarean section include paravertebral nerve block, transversus abdominis plane block, rectus sheath block, quadratus lumborum block, ilioinguinal-iliohypogastric nerve block, erector spinae block, wound infiltration analgesia, and intraperitoneal infusion of local anesthetics. These regional block techniques hold great promise for providing effective postoperative analgesia after cesarean section, each with unique advantages. Moreover, regional blocks have a unique place in multimodal analgesia protocols following cesarean section and are increasingly used in clinical practice for analgesia after cesarean section. This review provides an overview of the regional nerve block techniques used for postoperative analgesia following cesarean section, discusses their benefits and drawbacks, and provides a reference for choosing postoperative pain management following cesarean delivery, offering a hopeful outlook for improved patient care.

Multifocal motor neuropathy in Japan: A nationwide survey on prevalence, clinical profiles, and treatment.

Multifocal motor neuropathy (MMN) is a rare disease for which epidemiological and clinical data are limited. We conducted a nationwide survey to determine disease prevalence, incidence, clinical profile, and current treatment status in Japan. A nationwide survey was conducted in 2021 using an established epidemiological method. Questionnaires were sent to all neurology and pediatric neurology departments in Japan. An initial questionnaire was administered to determine the number of patients with and incidence of MMN. A second questionnaire was administered to collect detailed clinical information. The European Federation of Neurological Societies/Peripheral Nerve Society 2010 guidelines were used as diagnostic criteria. The estimated number of patients with MMN was 507. The estimated prevalence was 0.40 per 100,000 individuals. Detailed clinical profiles were available for 120 patients. The male-to-female ratio was 2.3:1 and the median onset age was 42 years. The median disease duration at diagnosis was 25 months. Most patients presented with upper limb-dominant muscle weakness. Motor nerve conduction blocks were found in 62% of patients and positive anti-GM1 IgM antibody results in 54%. A total of 117 (98%) patients received immunoglobulin therapy, and 91% of them showed improvement. At the time of the last visit (median, 82 months from treatment initiation), 89 (74%) patients were receiving maintenance immunoglobulin therapy. A slight progression of neurological deficits was observed during follow-up. Most patients with MMN in Japan received induction and maintenance immunoglobulin therapies, which appear to suppress long-term disease progression.

The Duration and Intensity of High Frequency Alternating Current Influences the Degree and Recovery of Nerve Conduction Block.

The purpose of this paper is to investigate the persistence of nerve blockade beyond the duration of applying high frequency alternating current (HFAC) to thinly myelinated and non-myelinated fibers, also termed a "carry-over effect". In this study, we used electrically-evoked compound action potentials from isolated rat vagus nerves to assess the influence of 5 kHz HFAC amplitude and duration on the degree of the carry-over effect. Current amplitudes from 1-10 mA and 5 kHz durations from 10-120 seconds were tested. By testing 20 different combinations of 5 kHz amplitude and duration, we found a significant interaction between 5 kHz amplitude and duration on influencing the carry-over effect. The degree of carry-over effect was dependent on 5 kHz amplitude, as well as duration. Utilizing the carry-over effect may be useful in designing energy efficient nerve blocking algorithms for the treatment of diseases influenced by nerve activity.

Progressive demyelinating polyneuropathy after hematopoietic cell transplantation in metachromatic leukodystrophy: a case series

Metachromatic leukodystrophy (MLD) is a neuro-metabolic disorder due to arylsulfatase A deficiency, causing demyelination of the central and peripheral nervous system. Hematopoietic cell transplantation (HCT) can provide a symptomatic and survival benefit for pre-symptomatic and early symptomatic patients by stabilizing CNS disease. This case series, however, illustrates the occurrence of severely progressive polyneuropathy shortly after HCT in two patients with late-infantile, one with late-juvenile, and one with adult MLD, leading to the inability to walk or sit without support. The patients had demyelinating polyneuropathy before HCT, performed at the ages of 2 years in the first two patients and at 14 and 23 years in the other two patients. The myeloablative conditioning regimen consisted of busulfan, fludarabine and, in one case, rituximab, with anti-thymocyte globulin, cyclosporine, steroids, and/or mycophenolate mofetil for GvHD prophylaxis. Polyneuropathy after HCT progressed parallel with tapering immunosuppression and paralleled bouts of infection and graft-versus-host disease (GvHD). Differential diagnoses included MLD progression, neurological GvHD or another (auto)inflammatory cause. Laboratory, electroneurography and pathology investigations were inconclusive. In two patients, treatment with immunomodulatory drugs led to temporary improvement, but not sustained stabilization of polyneuropathy. One patient showed recovery to pre-HCT functioning, except for a Holmes-like tremor, for which a peripheral origin cannot be excluded. One patient showed marginal response to immunosuppressive treatment and died ten months after HCT due to respiratory failure. The extensive diagnostic and therapeutic attempts highlight the challenge of characterizing and treating progressive polyneuropathy in patients with MLD shortly after HCT. We advise to consider repeat electro-neurography and possibly peripheral nerve biopsy in such patients. Nerve conduction blocks, evidence of the presence of T lymphocytes and macrophages in the neuronal and surrounding nerve tissue, and beneficial effects of immunomodulatory drugs may indicate a partially (auto)immune-mediated pathology. Polyneuropathy may cause major residual disease burden after HCT. MLD patients with progressive polyneuropathy could potentially benefit from a more intensified immunomodulatory drug regime following HCT, especially at times of immune activation.

142 Common Peroneal Nerve Decompression for Slimmers Palsy: A Case Series With Intraoperative Stimulation

INTRODUCTION: Slimmer’s palsy refers to common peroneal nerve (CPN) entrapment neuropathy associated with rapid or significant weight loss. Indications and outcomes for CPN decompression in this population remain unclear. While there are reports documenting functional improvement after surgical decompression, there are also case series demonstrating recovery with non-operative management, including diet modification, nutritional supplementation, and rehabilitation. METHODS: Retrospective chart review was performed to identify patients (age >18) who underwent CPN decompression between 2012-2021 with documented history of weight loss >5 kg. Demographics, weight loss, operative details, electromyography findings, onset/degree of weakness by manual muscle testing (MMT), and extent of improvement were collected. Pre- and post-decompression conduction thresholds were measured intraoperatively. Descriptive statistics were performed, including paired t-tests for pre- and post-operative MMT scores and pre- and post-decompression conduction thresholds. RESULTS: Five total patients were identified. Median age was 39 years. Most were male (3/5), White (5/5), privately insured (3/5), current/former smokers (3/5), and normal weight (3/5). Mean weight loss was 27 kg (range: 5-45). Reasons for weight loss included intentional, chemotherapy-related, bariatric surgery, and one case of unexplained weight loss. Mean MMT score at time of evaluation was 2.0 + 0.45 for tibialis anterior (TA), 2.0 + 0.55 for extensor hallucis longus (EHL) and 2.2 + 0.58 for peroneus longus (PL). Time to surgery ranged from 4-6 months. Mean postoperative MMT scores were significantly improved in TA (4.6 + 0.24, p = 0.007), EHL (4.6 + 0.24, p = 0.007) and PL (4.6 + 0.24, p = 0.02) compared to baseline. Mean conduction thresholds (5.75 + 1.89) were lower after decompression (1.2 + 0.31), although not statistically significant in this sample (p = 0.12). CONCLUSIONS: In this small series, CPN decompression restored function for patients with Slimmer’s palsy. Nerve conduction block was observed intraoperatively in most cases, perhaps supporting a compressive etiology for this condition.

Docking protein 6 (DOK6) selectively docks the neurotrophic signaling transduction to restrain peripheral neuropathy

The appropriate and specific response of nerve cells to various external cues is essential for the establishment and maintenance of neural circuits, and this process requires the proper recruitment of adaptor molecules to selectively activate downstream pathways. Here, we identified that DOK6, a member of the Dok (downstream of tyrosine kinases) family, is required for the maintenance of peripheral axons, and that loss of Dok6 can cause typical peripheral neuropathy symptoms in mice, manifested as impaired sensory, abnormal posture, paw deformities, blocked nerve conduction, and dysmyelination. Furthermore, Dok6 is highly expressed in peripheral neurons but not in Schwann cells, and genetic deletion of Dok6 in peripheral neurons led to typical peripheral myelin outfolding, axon destruction, and hindered retrograde axonal transport. Specifically, DOK6 acts as an adaptor protein for selectivity-mediated neurotrophic signal transduction and retrograde transport for TrkC and Ret but not for TrkA and TrkB. DOK6 interacts with certain proteins in the trafficking machinery and controls their phosphorylation, including MAP1B, Tau and Dynein for axonal transport, and specifically activates the downstream ERK1/2 kinase pathway to maintain axonal survival and homeostasis. This finding provides new clues to potential insights into the pathogenesis and treatment of hereditary peripheral neuropathies and other degenerative diseases.

Multifocal Acquired Demyelinating Sensory and Motor Neuropathy (MADSAM) with Cranial Nerve Involvement. Case Report

BACKGROUND: The multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) is a rare adult onset subvariant of the chronic inflammatory demyelinating polyneuropathy (CIDP). The latter affects 1-9 cases per million adults and may pose a diagnostic challenge (antibody and electrophysiological overlap). The hallmark of the disease spectrum is an immune mediated structural myelin breakdown. Urgent differentiation of MADSAM from the other variants of CIDP is indicated due to its distinct pathogenesis, management, and long-term therapy response to immunomodulators. The disease presents with progressive asymmetrical motor and sensory deficits initially located typically in one limb. Rarely the disease manifests with cranial nerve involvement. The prognosis of patients suffering from MADSAM is reliant on rapid diagnosis and therapeutic response, but neurological deficits reside. Due to its rarity and diagnostic challenge, misdiagnosis is common. THE CASE: A 84 years old Caucasian male diagnosed with multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) presented to our department with progressive neurological deficits. His neurological examination and history revealed paresthesia, hypesthesia, diminished vibration sense (pallhypesthesia), distally pronounced paresis in the upper extremities with a wrist drop on the left hand. Gait examination exposed coordination deficits. The history of the patient and the initial presentation of the disease in 1998 exemplifies the diagnostic challenge of MADSAM, due its mimicry of other diseases, like multifocal motor neuropathy (MMN). The initial symptoms were asymmetrical motor and sensory deficit starting at the upper extremities. Before the patient presented to our facility, he was diagnosed with neuroborreliosis and treated accordingly. The correct diagnosis was set at our department according to clinical presentation, nerve conduction velocity parameters and conduction block during electroneurography, typical changes in nerve ultrasound suggesting an inflammatory neuropathy and fasciculations of the gastrocnemius muscle. After an ineffective steroid therapy and long standing intravenous immunoglobulins the patient is now on a therapeutic scheme of 1000mg Rituximab (CD20 Ab) every 6 months and 1000mg Mycophenolatmofetil. The patient subjectively reports improvement of his status and slower progression of the disease since the Rituximab paradigm. Furthermore, an evident atrophy of the orbicularis oculi muscle was now noted during follow up examination, which highlights facial nerve involvement. CONCLUSION: This case exemplifies the challenge of diagnosing the multifocal acquired sensory and motor neuropathy, but prompt diagnosis and therapeutic intervention is associated with a better prognosis and slower progression of the disease in patients suffering from MADSAM.

Towards a more accurate quasi-static approximation of the electric potential for neurostimulation with kilohertz-frequency sources * *This work has been partially supported by ANID Millennium Science Initiative Program through Millennium Nucleus for Applied Control and Inverse Problems NCN19-161.

Objective. Our goal was to determine the conditions for which a more precise calculation of the electric potential than the quasi-static approximation may be needed in models of electrical neurostimulation, particularly for signals with kilohertz-frequency components. Approach. We conducted a comprehensive quantitative study of the differences in nerve fiber activation and conduction block when using the quasi-static and Helmholtz approximations for the electric potential in a model of electrical neurostimulation. Main results. We first show that the potentials generated by sources of unbalanced pulses exhibit different transients as compared to those of charge-balanced pulses, and this is disregarded by the quasi-static assumption. Secondly, relative errors for current-distance curves were below 3%, while for strength-duration curves these ranged between 1%–17%, but could be improved to less than 3% across the range of pulse duration by providing a corrected quasi-static conductivity. Third, we extended our analysis to trains of pulses and reported a ‘congruence area’ below 700 Hz, where the fidelity of fiber responses is maximal for supra-threshold stimulation. Further examination of waveforms and polarities revealed similar fidelities in the congruence area, but significant differences were observed beyond this area. However, the spike-train distance revealed differences in activation patterns when comparing the response generated by each model. Finally, in simulations of conduction-block, we found that block thresholds exhibited errors above 20% for repetition rates above 10 kHz. Yet, employing a corrected value of the conductivity improved the agreement between models, with errors no greater than 8%. Significance. Our results emphasize that the quasi-static approximation cannot be naively extended to electrical stimulation with high-frequency components, and notable differences can be observed in activation patterns. As well, we introduce a methodology to obtain more precise model responses using the quasi-static approach, retaining its simplicity, which can be a valuable resource in computational neuroengineering.

Rapid Functional Recovery After Thoracic Outlet Decompression in a Series of Adolescent Athletes With Chronic Atraumatic Shoulder-Girdle Pain, Scapular Winging/Dyskinesis, and Normal Electrodiagnostic Studies.

Spontaneous shoulder-girdle pain and scapular winging/dyskinesis can be caused by several neuromuscular disorders identifiable by electrodiagnostic studies (EDX). We describe a group of adolescent athletes with this clinical presentation but normal EDX, followed by later development of neurogenic thoracic outlet syndrome (NTOS). We identified patients referred for evaluation of NTOS that had a history of chronic atraumatic shoulder-girdle pain, scapular winging/dyskinesis, and normal EDX. Each was refractory to conservative management and underwent supraclavicular decompression and brachial plexus neurolysis for NTOS. Functional disability was quantified by Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH) scores. There were 5 female patients with a mean age at symptom onset of 14.2 ± 0.4 years, including spontaneous severe pain in the shoulder, scapula, and arm, along with prominent scapular winging/dyskinesis, and normal EDX. Symptoms had persisted for 18.9 ± 4.0 months prior to referral, with pronounced upper extremity disability (mean QuickDASH, 54.6 ± 6.9). By 3 months after surgical treatment for NTOS, all 5 patients experienced near-complete symptom resolution, including scapular winging/dyskinesis, with markedly improved function (mean QuickDASH, 2.2 ± 1.3) and a return to normal activity. A subset of patients with chronic atraumatic shoulder-girdle pain, scapular winging/dyskinesis, and normal EDX may develop dynamic brachial plexus compression characteristic of NTOS, exhibiting an ischemic "Sunderland-zero" nerve conduction block for which surgical decompression can result in rapid and substantial clinical improvement. The presence of surgically treatable NTOS should be considered for selected patients with long-standing scapular winging/dyskinesis who fail conservative management.

Clinical and neurophysiological recovery of ulnar nerve conduction block at the elbow.

An important mechanism of peripheral nerve motor and sensory dysfunction is conduction block (CB). However, recovery from mechanically induced CB has been rarely studied in humans. The aim of this study was to describe clinical, electrodiagnostic (EDx), and ultrasonographic (US) characteristics of CB recovery in ulnar neuropathy at the elbow (UNE). We recruited a group of consecutive patients presenting to our EDx laboratory with UNE and >50% motor CB. Patients' histories were obtained and neurologic, EDx, and US examinations were repeated every 1-3 mo for at least 12 mo. We studied 10 patients (5 men), with a mean age of 63 y (range, 51-81 y). In all affected arms CB was localized to the retrocondylar groove. Following conservative management, myometrically measured index finger abduction improved from a median of 49% to 100% relative to the contralateral index finger, and ulnar nerve CB decreased from a median of 74% to 6%. Most of the improvement took place within 8 mo of symptom onset, and 6 mo after receiving treatment instructions. Mean motor nerve conduction velocity improved from 15 to 27 m/s in the most affected 2-cm ulnar nerve segment. The resolution of CB after typical chronic compression may take longer than after acute compression. This should be considered by clinicians when estimating prognosis for discussions with patients.

Spatiotemporal parameters for energy efficient kilohertz-frequency nerve block with low onset response

BackgroundElectrical nerve conduction block has great potential for treatment of disease through reversible and local inactivation of somatic and autonomic nerves. However, the relatively high energy requirements and the presence of undesired excitation at the onset of the kilohertz-frequency (KHF) signals used for block pose obstacles to effective translation. Frequency, electrode geometry, and waveform shape are known to influence block threshold and onset response, but available data provide a limited understanding of how to select these parameters to optimize nerve block.MethodsWe evaluated KHF nerve block in rat tibial nerve across frequencies (5–60 kHz), electrode geometries (monopolar, bipolar, and tripolar), and waveform shapes. We present a novel Fourier-based method for constructing composite signals that systematically sample the KHF waveform design space.ResultsThe lowest frequencies capable of blocking (5–16 kHz) were not the most energy-efficient among the tested frequencies. Further, bipolar cuffs required the largest current and power to block, monopolar cuffs required the lowest current, and both tripolar and monopolar cuffs required the lowest power. Tripolar cuffs produced the smallest onset response across frequencies. Composite signals comprised of a first harmonic sinusoid at fundamental frequency (f0) superposed on a second harmonic sinusoid at 2f0 could block at lower threshold and lower onset response compared to the constituent sinusoids alone. This effect was strongly dependent on the phase of the second harmonic and on the relative amplitudes of the first and second harmonics. This effect was also dependent on electrode geometry: monopolar and tripolar cuffs showed clear composite signal effects in most experiments; bipolar cuffs showed no clear effects in most experiments.ConclusionsOur data provide novel information about block threshold and onset response at the boundary of frequencies that can block. Our results also show an interaction between spatial (cuff geometry) and temporal (frequency and waveform shape) parameters. Finally, while previous studies suggested that temporal parameters could reduce onset response only in exchange for increased block threshold (or vice versa), our results show that waveform shape influences KHF response in ways that can be exploited to reduce both energy and onset responses.

Pudendal Nerve Block by Adaptively Stepwise Increasing the Intensity of High-Frequency (10 kHz) Biphasic Stimulation

ObjectiveThe purpose of this study is to determine whether adaptively stepwise increasing the intensity of a high-frequency (10 kHz) biphasic stimulation (HFBS) can produce nerve conduction block without generating a large initial response. Materials and MethodsIn anesthetized cats, three cuff electrodes were implanted on the left pudendal nerve for stimulation or block. The urethral pressure increase induced by pudendal nerve stimulation was used to measure the pudendal nerve block induced by HFBS. ResultsHFBS applied suddenly with a large step increase in intensity induced a large (86 ± 16 cmH2O) urethral pressure increase before it blocked pudendal nerve conduction. However, HFBS applied by adaptively stepwise increasing the intensity every 10 to 60 seconds over a long period (33–301 minutes; average 108 ± 35 minutes) with many small intensity increases (0.005–0.1 mA) induced no response or low-amplitude high-frequency urethral pressure changes before it blocked pudendal nerve conduction. The minimal HFBS intensities required by the two different methods to block pudendal nerve conduction are similar. ConclusionThis study is important for better understanding the possible mechanisms underlying the HFBS-induced nerve block and provides the possibility of developing a new nerve block method for clinical applications in which an initial large response is a concern.

A multicenter, randomized, double blind, placebo-controlled clinical trial of dl-3-butylphthalide in treatment of amyotrophic lateral sclerosis.

A multicenter, randomized, double blind, placebo-controlled clinical trial of dl-3-butylphthalide in treatment of amyotrophic lateral sclerosis.

ПРОДЛЁННАЯ ПЛЕКСУСНАЯ БЛОКАДА ПРИ ОПЕРАТИВНЫХ ВМЕШАТЕЛЬСТВАХ НА ВЕРХНИХ КОНЕЧНОСТЯХ

This article overviews the various prolonged plexus block (PB) methods. It discusses the indications and contraindications for this technique and the professional skills and equipment needed. The article also describes different approaches to a brachial plexus block (BPB): interscalene, supraclavicular, infraclavicular, and axillary. The article presents the rationale for using PB, its advantages and possible complications, and outlines the basic principles for its safe performance. Knowledge of anatomical and topographic landmarks, ultrasound navigation, and neurostimulation are utilized to determine needle position. Neurostimulation should be used to ensure the needle is placed correctly to achieve a muscle response with a current of 0.3-0.5 mA. A muscle response with a current of 0.2 mA occurs only when the needle tip is positioned intraneurally, which is unacceptable when performing plexus and nerve conduction blocks. This technique can provide prolonged anesthesia and postoperative pain relief by correctly and safely blocking nerve plexuses and trunks. It is an ideal option for anaesthesiologic support during surgical interventions and treating postoperative pain. This approach has many advantages and does not have the disadvantages associated with other types of local and general anesthesia. In this literature review, we used databases such as eLIBRARY, PubMed, and Google Scholar to search for articles related to regional anesthesia, specifically, BPB. We narrowed our search by using keywords including ultrasound navigation, neurostimulation, and catheter-based techniques. Keywords: Brachial plexus, regional anesthesia, prolonged plexus block, ultrasound navigation, neurostimulation, catheter-based techniques.

Effect ofclonidine on heart rate variability during spinal anaesthesia: randomized clinical trial.

Spinal anaesthesia consists of administering a local anaesthetic in the subarachnoid space, thus causing sensory, motor, and autonomic nerve conduction block. Currently, recovery from spinal anaesthesia is evaluated by the return of motor function, without considering the autonomic blockade, which is responsible for most complications of the technique. Heart rate variability (HRV) is an indirect method to measure the autonomic nervous system and may be useful in assessing autonomic recovery after spinal anaesthesia. The study objective was to evaluate the autonomic function, through HRV, at the moment of return of motor function in patients who received spinal anaesthesia when clonidine is used as an adjuvant. This was a randomised, double-blind clinical trial. The sample consisted of 64 ASA I-II patients who underwent spinal anaesthesia and were divided into 2 groups. Group C received 20 mg of bupivacaine with 75 mcg of clonidine, and group B received 20 mg of bupivacaine. HRV was evaluated at rest (T1) and at the time of motor function recovery (T2). Data were collected using a Polar V800® heart rate monitor and then analysed and filtered using Kubios 3.0® software. There was no difference in the values of the low-frequency/high-frequency (LF/HF) ratio, Poincaré plot standard deviation (SD2/SD1), detrended fluctuation analysis (DFAα1, DFAα2), or correlation dimension (D2) indices in any of the groups between the 2 moments. In the clonidine group, there was a difference only in approximate entropy (ApEn), where a P of 0.0124 was obtained considering a 95% confidence interval ranging from 17.83 to 141.47. There was no significant difference between the duration of sympathetic blockade and motor blockade in spinal anaesthesia.

Pain Management During Labor and Delivery in a Patient with Possible Local Anesthetic Resistance: A Case Report

Background: Local anesthetic resistance is a clinical entity characterized by inadequate analgesia despite technically well-performed procedures. The exact etiology and pathogenesis of this condition are not yet fully understood. Case Presentation: A 36-year-old Caucasian female presented to labor and delivery for induction of labor. On admission, the patient reported failure of epidural anesthesia during the previous delivery. An epidural catheter was placed, and analgesia was reported only at high doses of local anesthetic. The patient’s maximum pain level during delivery never reached a score of 2 out of 10. Conclusion: The most common causes of regional anesthetic failure are technical or placement failure, failure related to the local anesthetic itself, or localized infection. This patient appeared to have a true local anesthetic resistance, which was overcome by doubling the customary concentration of local anesthetic. Atypical responses to local anesthetics observed in the patient may be due to incomplete penetrance mutations in sodium channels since local anesthetics work through blocking nerve conduction by acting on these channels.

TH-142. Clinical and neurophysiological recovery after ulnar nerve conduction block at the elbow

TH-142. Clinical and neurophysiological recovery after ulnar nerve conduction block at the elbow

Effects of waveform shape and electrode material on KiloHertz frequency alternating current block of mammalian peripheral nerve

ObjectivesKiloHertz frequency alternating current waveforms produce conduction block in peripheral nerves. It is not clearly known how the waveform shape affects block outcomes, and if waveform effects are frequency dependent. We determined the effects of waveform shape using two types of electrodes.Materials and methodsAcute in-vivo experiments were performed on 12 rats. Bipolar electrodes were used to electrically block motor nerve impulses in the sciatic nerve, as measured using force output from the gastrocnemius muscle. Three blocking waveforms were delivered (sinusoidal, square and triangular) at 6 frequencies (10–60 kHz). Bare platinum electrodes were compared with carbon black coated electrodes. We determined the minimum amplitude that could completely block motor nerve conduction (block threshold), and measured properties of the onset response, which is a transient period of nerve activation at the start of block. In-vivo results were compared with computational modeling conducted using the NEURON simulation environment using a nerve membrane model modified for stimulation in the kilohertz frequency range.ResultsFor the majority of parameters, in-vivo testing and simulations showed similar results: Block thresholds increased linearly with frequency for all three waveforms. Block thresholds were significantly different between waveforms; lowest for the square waveform and highest for triangular waveform. When converted to charge per cycle, square waveforms required the maximum charge per phase, and triangular waveforms the least. Onset parameters were affected by blocking frequency but not by waveform shape. Electrode comparisons were performed only in-vivo. Electrodes with carbon black coatings gave significantly lower block thresholds and reduced onset responses across all blocking frequencies. For 10 and 20 kHz, carbon black coating significantly reduced the charge required for nerve block.ConclusionsWe conclude that both sinusoidal and square waveforms at frequencies of 20 kHz or higher would be optimal. Future investigation of carbon black or other high charge capacity electrodes may be useful in achieving block with lower BTs and onsets. These findings will be of importance for designing clinical nerve block systems.

In vivo peripheral nerve activation using sinusoidal low-frequency alternating currents.

The sinusoidal low-frequency alternating current (LFAC) waveform was explored recently as a novel means to evoke nerve conduction block. In the present work, we explored whether increasing the amplitude of the LFAC waveform results in nerve fiber activation in autonomic nerves. In-silico methods and preliminary work in somatic nerves indicated a potential frequency dependency on the threshold of activation. The Hering-Breuer (HB) reflex was used as a biomarker to detect cervical vagus nerve activation. Experiments were conducted in isoflurane-anesthetized swine (n=5). Two stimulating bipolar cuff electrodes and a tripolar recording cuff electrode were implanted on the left vagus nerve. To ensure the electrical stimulation affects only the afferent pathways, the nerve was crushed caudal to the electrodes to eliminate cardiac effects. (1) Standard pulse stimulation (Vstim) using a monophasic train of pulses was applied through the caudal electrode to elicit HB reflex and to identify the activated nerve fiber type. (2) Continuous sinusoidal LFAC waveform with a frequency ranging from 5 through 20 Hz was applied to the rostral electrode without Vstim to explore the activation thresholds at each LFAC frequency. In both cases, the activation of nerve fibers was detected by a HB reflex-induced reduction in the breathing rate. LFAC was found to be capable of eliciting an HB response. The LFAC activation thresholds were found to be frequency-dependent. The HB threshold was 1.02 ± 0.3 mAp at 5Hz, 0.66 ± 0.3 mAp at 10Hz, and 0.44 ± 0.2 mAp at 20 Hz. In comparison, it was 0.7 ± 0.47 mA for a 100 μs pulse. The LFAC amplitude was within the linear limits of the electrode interface. Damage to the cuff electrodes or the nerve tissues was not observed. Analysis of Vstim-based compound nerve action potentials (CNAP) indicated that the decrease in breathing rate was found to be correlated with the activation of slower components of the CNAP suggesting that LFAC reached and elicited responses from these slower fibers associated with afferents projecting to the HB response. These results suggest the feasibility of the LFAC waveform at 5, 10, and 20 Hz to activate autonomic nerve fibers and potentially provide a new modality to the neurorehabilitation field.