Single Fiber Action Potentials Research Articles

Simulated Surface Electromyographic (SEMG) Signal Generation and Detection Model

Abstract For didactic purposes, the aim of this work was to improve a simulation model of surface electromyographic (sEMG) signal by taking into consideration the shortcomings of previously developed models. This model started with the simulation of the single fibre action potential (SFAP), then the model of the single motor unit action potential (MUAP), afterwards the imitation of the train of MUAP and finally the modellig of the resultant sEMG signal which is the sum of the MUAPs trains. SFAP simulation was based on: i) the description of the volume conductor model which is composed of four layers (bone, muscle, fat and skin), ii) the description of the electrodes shapes and sizes as well as spatial filters, iii) and the transmebrane current. The proposed model shows its effectiveness in the possibility of carrying out practical work by simulation on the modelling of SFAP, MUAP, MUAPT and the sEMG signal. The most important result of this model is that signal processing tools can be applied to analyze and interpret real-world phenomena such as the effects of physiological, non physiological and sensing system parameters on the shape of the simulated sEMG signal.

Neuromuscular junction transmission failure in aging and sarcopenia: The nexus of the neurological and muscular systems.

Sarcopenia, or age-related decline in muscle form and function, exerts high personal, societal, and economic burdens when untreated. Integrity and function of the neuromuscular junction (NMJ), as the nexus between the nervous and muscular systems, is critical for input and dependable neural control of muscle force generation. As such, the NMJ has long been a site of keen interest in the context of skeletal muscle function deficits during aging and in the context of sarcopenia. Historically, changes of NMJ morphology during aging have been investigated extensively but primarily in aged rodent models. Aged rodents have consistently shown features of NMJ endplate fragmentation and denervation. Yet, the presence of NMJ changes in older humans remains controversial, and conflicting findings have been reported. This review article describes the physiological processes involved in NMJ transmission, discusses the evidence that supports NMJ transmission failure as a possible contributor to sarcopenia, and speculates on the potential of targeting these defects for therapeutic development. The technical approaches that are available for assessment of NMJ transmission, whether each approach has been applied in the context of aging and sarcopenia, and the associated findings are summarized. Like morphological studies, age-related NMJ transmission deficits have primarily been studied in rodents. In preclinical studies, isolated synaptic electrophysiology recordings of endplate currentsor potentials have been mostly used, and paradoxically, have shown enhancement, rather than failure, with aging. Yet, in vivo assessment of single muscle fiber action potential generation using single fiber electromyography and nerve-stimulated muscle force measurements show evidence of NMJ failure in aged mice and rats. Together these findings suggest that endplate response enhancement may be a compensatory response to post-synaptic mechanisms of NMJ transmission failure in aged rodents. Possible, but underexplored, mechanisms of this failure are discussed including the simplification of post-synaptic folding and altered voltage-gated sodium channel clustering or function. In humans, there is limited clinical data that has selectively investigated single synaptic function in the context of aging. If sarcopenic older adults turn out to exhibit notable impairments in NMJ transmission (this has yet to be examined but based on available evidence appears to be plausible) then these NMJ transmission defects present a well-defined biological mechanism and offer a well-defined pathway for clinical implementation. Investigation of small molecules that are currently available clinically or being testing clinically in other disorders may provide a rapid route for development of interventions for older adults impacted by sarcopenia.

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.

Investigation of an Acceleration Pipeline for Single Fiber Action Potential Simulation

Abstract Surface electromyography (sEMG) records the electrical potentials on the skin surface generated by the electrical activity of muscle fibers. To better understand physiology and to assess signal processing algorithms, sEMG models have been developed in the past. However, numerical models required for modeling accurate geometries very often have a high computational complexity rendering realistic simulations challenging. In order to cope with this challenge, a pipeline is investigated to accelerate the calculation of the single fiber action potential (SFAP) based on the principle of reciprocity. To enable a comparison to an analytical solution, the investigation is carried out in a highly simplified muscle model. The results show that the pipeline is suitable for calculating SFAP with a low mean absolute error sufficient for application in sEMG models. In addition, there is a significant reduction of the calculation time allowing the simulation of even highly complex geometries and a large number of muscle fibers.

Near-tendon single-fiber electromyography in patients with myopathy

We investigated how properties of single-fiber action potentials (SFAP) and jitter changed in different recording sites in patients with myopathy and controls. SFAP and jitter were recorded using a disposable single-fiber electrode in the biceps brachii muscle of three patients and controls in two sites: i) near the end-plate zone (EPZ), ii) near the tendon. SFAP and spike duration were longer in patients than in controls. Moving the needle away from the EPZ did not change the electrophysiologic parameters. Longer SFAP duration may reflect slow velocity in muscle fibers and serve as an indicator for small fiber size in myopathy.

Analytical Modelling of Surface EMG Signals Generated by Curvilinear Fibers With Approximate Conductivity Tensor.

Mathematical modelling of surface electromyographic (EMG) signals has been proven a valuable tool to interpret experimental data and to validate signal processing techniques. Most analytical EMG models only consider muscle fibers with specific arrangements. However, the fiber orientation may change along the fiber paths and differ from fiber to fiber. Here we propose a subject-specific EMG model that simulates the fiber trajectories in muscles of the upper arm and analytically derives the action potentials assuming an approximate conductivity tensor. Magnetic Resonance (MR) images were acquired to generate muscle fiber paths and to build the volume conductor. While the action potentials propagated along the identified curvilinear fibers, the conductivity tensor was approximated to be cylindrically anisotropic. Single fiber action potentials (SFAPs) were computed by simulating the generation, propagation, and extinction of membrane current sources. To validate the assumption of the approximate conductivity tensor, two numerical models with approximate or exact conductivity tensors were implemented. The motor unit action potentials generated by the proposed analytical model and the two numerical models were highly similar (cross-correlation 0.98, normalized root mean square error, nRMSE ≤ 0.04, relative error in the median frequency of the simulated waveforms of approximately 3%). The proposed analytical model was also evaluated by comparing simulated and experimentally recorded compound muscle action potentials (CMAPs). Finally, the proposed model was used to test the accuracy of an EMG decomposition algorithm, providing a realistic benchmark. The proposed analytical model generates action potentials that reflect the spatial distributions of muscle fibers with curvilinear paths.

Automated Biomedical Signal Quality Assessment of Electromyograms: Current Challenges and Future Prospects

This work is an exposition of research supporting efforts to automate quality assessment in surface electromyography (sEMG). Electromyography measures electrical activity from skeletal muscles, which are the muscles associated with voluntary movements. Skeletal muscles can consist of tens to hundreds of thousands of contractile fibers which are grouped into functional units called Motor Units (MUs). Each MU is driven to contract its fibers by electrochemical impulses sent from a motor neuron, and a muscle may contain anywhere from tens to hundreds of MUs. When an MU is activated, all fibers associated with it are simultaneously activated. When fibers are activated, an electrochemical impulse propagates along each of them to cause contraction. This impulse is known as a Single Fiber Action Potential (SFAP). A Motor Unit Action Potential (MUAP) is the summation of all SFAPs corresponding to an activated MU. To generate a continuous contraction, MUs are repeatedly activated, producing a train of MUAPs, and this pulse train is called the Motor Unit Action Potential Train (MUAPT). The combined electrical activity of all of the MUAPTs associated with a contraction, as recorded on the surface of the skin using non-invasive electrodes, is a surface electromyography (sEMG) signal. In general, it is not possible to directly observe the SFAPs, MUAPs, and MUAPTs non-invasively (though there have been algorithmic efforts to decompose sEMG signals into its constituent MUAPTs). SFAPs and MUAPTs can be observed by inserting needle electrodes into specific muscle regions for high spatial selectivity; however, such techniques are invasive, making surface measurements a desirable alternative. sEMG signals have been used in a wide variety of applications, including fatigue assessment, myoelectric control, diagnosis of neuromuscular disorders, and tracking performance in sports.

Effects of muscle shortening on single-fiber, motor unit, and compound muscle action potentials

Even under isometric conditions, muscle contractions are associated with some degree of fiber shortening. The effects of muscle shortening on extracellular electromyographic potentials have not been characterized in detail. Moreover, the anatomical, biophysical, and detection factors influencing the muscle-shortening effects have been neither identified nor understood completely. Herein, we investigated the effects of muscle shortening on the amplitude and duration characteristics of single-fiber, motor unit, and compound muscle action potentials. We found that, at the single-fiber level, two main factors influenced the muscle-shortening effects: (1) the electrode position and distance relative to the myotendinous zone and (2) the electrode distance to the maxima of the dipole field arising from the stationary dipole created at the fiber-tendon junction. Besides, at the motor unit and muscle level, two additional factors were involved: (3) the overlapping between the propagating component of some fibers with the non-propagating component of other fibers and (4) the spatial spreading of the fiber-tendon junctions. The muscle-shortening effects depend critically on the electrode longitudinal distance to the myotendinous zone. When the electrode was placed far from the myotendinous zone, muscle shortening resulted in an enlargement and narrowing of the final (negative) phase of the potential, and this enlargement became less pronounced as the electrode approached the fiber endings. For electrode locations close to the myotendinous zone, muscle shortening caused a depression of both the main (positive) and final (negative) phases of the potential. Beyond the myotendinous zone, muscle shortening led to a decrease of the final (positive) phase. The present results provide reference information that will help to identify changes in MUPs and M waves due to muscle shortening, and thus to differentiate these changes from those caused by muscle fatigue.Graphical abstract

Marching band model for simulating a single muscle fiber action potential

ObjectiveWe describe a mathematical model to calculate a single muscle fiber action potential (AP). Based on a marching band pattern, it is an enhancement to our previously described “modified line source” model. MethodsCalculations were performed using an Excel spread sheet. AP was simulated for a 200 mm long muscle fiber with 60 µm diameter, propagation velocity of 4 m/s, and end-plate located at the center. Several different electrode locations were used to calculate the AP. ResultsThe AP amplitude was highest at the end-plate where the waveform was biphasic with initial negativity. When the electrode was moved towards the tendon, the amplitude decreased for the first 1.5 mm. The AP was triphasic and its waveform was relatively constant at electrode positions beyond 1.5 mm from the end-plate. It matched the calculations using the modified line source model. When the electrode was near the tendon, the AP amplitude decreased asymmetrically and waveform became biphasic resembling a positive sharp wave. DiscussionThe model is conceptually and computationally simple. It simulated the expected AP shape at different electrode positions along the muscle fiber. The waveforms are similar to those obtained from mathematically complex volume conductor models. SignificanceThe revised model can be useful for teaching and future simulation studies.

Muscle Fiber Diameter and Density Alterations after Stroke Examined by Single-Fiber EMG.

This study presents single-fiber electromyography (EMG) analysis for assessment of paretic muscle changes after stroke. Single-fiber action potentials (SFAPs) were recorded from the first dorsal interosseous (FDI) muscle bilaterally in 12 individuals with hemiparetic stroke. The SFAP parameters, including the negative peak duration and the peak-peak amplitude, were measured and further used to estimate muscle fiber diameter through a model based on the quadratic function. The SFAP parameters, fiber density, and muscle fiber diameter derived from the model were compared between the paretic and contralateral muscles. The results show that SFAPs recorded from the paretic muscle had significantly smaller negative peak duration than that from the contralateral muscle. As a result, the derived muscle fiber diameter of the paretic muscle was significantly smaller than that of the contralateral muscle. The fiber density of the paretic muscle was significantly higher than that of the contralateral muscle. These results provide further evidence of remodeled motor units after stroke and suggest that paretic muscle weakness can be due to both complex central and peripheral neuromuscular alterations.

WS6.2. Stimulation single-fibre EMG: Methods and pitfalls (with demonstration)

Single-fiber electromyography (SFEMG) is a technique introduced by Prof. Stålberg and his colleagues in 1970’s. SFEMG electrode has the smallest uptake area (0.3 mm in radius) among EMG electrodes, and therefore can identify action potentials of individual muscle fibers (single fiber action potentials; SFAPs) comprising the motor unit by applying a very high low- cut filter (500 Hz). Recently, disposable concentric needle is commonly used in place of reusable SFEMG needle (CN-SFEMG). By setting an even higher low-cut filter (1 or 2 kHz), individual SFAPs can be identified even using the concentric needle. There are two recording methods of SFEMG, during voluntary contraction (v-SFEMG) and following axonal stimulation (s-SFEMG). Both methods have merits and demerits, and specific pitfalls. Patient cooperation is necessary for v-SFEMG but not for s-SFEMG, which is therefore applicable for comatose patients or small children. Examination time is usually believed to be shorter in s-SFEMG (I don’t think that this is always true). This is because only one SFAP is necessary in order to measure jitter in s-SFEMG, although two SFAPs recoded simultaneously are necessary in v-SFEMG. However, v-SFEMG is probably more sensitive in detecting neuromuscular junction (NMJ) dysfunction in myasthenia gravis (MG). Since SFEMG is expected to be more sensitive than repetitive nerve stimulation test, the sensitivity must be the most crucial issue. Therefore, I prefer v-SFEMG and conduct only v-SFEMG in daily practice. For s-SFEMG, monopolar stimulating needle is inserted close to the motor nerve or terminal nerve twigs (facial nerve branch lateral to the external canthus for frontalis recording). CN needle is inserted within the target muscle. We search sharp SFAPs during 5 to10 Hz test stimulation. When good SFAPs are identified, jitter is measured during 10 Hz stimulation. Submaximal stimulation is the greatest pitfall in s-SFEMG. Therefore, the threshold current is determined for each SFAP and an intensity 20% over the threshold is used for recording jitter. Very often, the target SFAP is blurred by the contamination of other SFAPs that have been newly-recruited while increasing the current intensity. This Is the reason why s-SFEMG takes longer time than usually considered.

WS6.3. Measuring jitter with concentric needle electrodes

Although it is preferable to use single fiber electrodes (SFEs) to measure jitter, concentric needle electrodes (CNEs) are increasingly used instead because of concern about transmissible diseases and the cost of SFEs. Increasing the low frequency filter to 1 kHz or higher produces CNE signals that appear identical to SF action potentials (APs), but such CNE signals frequently represent summation of many SFAPs – to emphasize this, simple spikes recorded with CNEs that resemble SFAPs have been called “apparent single fiber action potentials” (ASFAPs). Jitter in summated signals recorded with CNEs is somewhat less than the jitter in SFAPs. Thus, although increased jitter in CNE studies indicates abnormal neuromuscular transmission, mild abnormalities may not be detected as well as with SFEs unless appropriate reference values are used. Note – fiber density measurements can only be made with SFEs. The following precepts should be followed if CNEs are used for jitter measurements: • Use the CNE with the smallest recording surface. Currently this is the DCF 25 electrode, which is available from several vendors. Note – because of their large pickup area, monopolar needle electrodes are even more likely to record superimposed APs and should not be used for jitter analysis. • Use a high pass filter setting of 1 kHz. Because this will reduce the amplitude of recorded signals, spikes with amplitude as low as 50 μV are acceptable for jitter measurement if they have a rise time less than 300 μsec. • Measure jitter only from simple spikes that resemble SFAPs (ASFAPs). Do not measure jitter from spikes with a notch or “shoulder,” as these are definitely produced by more than one AP. • Use reference values for the specific CNE that you are using. We recommend that each laboratory obtain results from a small group of control subjects and compare these to published reference values, using the same techniques that were used to acquire those reference values, i.e., the specific type of electrode, filter settings, and criteria of acceptable APs.

Simulation study of spinal cord stimulation evoked compound action potential

Spinal cord stimulation (SCS) for pain is usually implanted as an open loop system using unchanged parameters. To avoid the under and over stimulation caused by lead migration, evoked compound action potentials (ECAP) is used as feedback signal to change the stimulating parameters. This study established a simulation model of ECAP recording to investigate the relationship between ECAP component and dorsal column (DC) fiber recruitment. Finite element model of SCS and multi-compartment model of sensory fiber were coupled to calculate the single fiber action potential (SFAP) caused by single fiber in different spinal cord regions. The synthetized ECAP, superimposition of SFAP, could be considered as an index of DC fiber excitation degree, because the position of crests and amplitude of ECAP corresponds to different fiber diameters. When 10% or less DC fibers were excited, the crests corresponded to fibers with large diameters. When 20% or more DC fibers were excited, ECAP showed a slow conduction crest, which corresponded to fibers with small diameters. The amplitude of this slow conduction crest increased as the stimulating intensity increased while the amplitude of the fast conduction crest almost remained unchanged. Therefore, the simulated ECAP signal in this paper could be used to evaluate the degree of excitation of DC fibers. This SCS-ECAP model may provide theoretical basis for future clinical application of close loop SCS base on ECAP.

Comparison of nerve conduction velocity distribution methods by cold exposure and ischemia

Purpose Non-invasive estimation of the conduction velocity distribution (CVD) of a peripheral nerve has the potential to both improve clinical diagnoses of pathology and to observe the progress of the disease or the efficacy of treatments. Comparisons were made of the performance of three non-invasive CVD estimation methods proposed by independent research groups on peripheral nerve bundles under different conditions. Methods The first method (Cummins) uses a nerve compound action potential (CAP) with temporal dispersion and a mathematical single fiber action potential (SFAP). The second method (Barker) uses two CAPs and a non-mathematical SFAP waveform. The third method (Hirose) uses two CAPs recorded from distal and proximal sites. The Cummins and Barker methods have iterative solutions in the time domain while the Hirose method is a deconvolution estimator in the frequency domain. In order to compare these methods, we used cold exposure to affect primarily motor fibers and ischemia to affect primarily sensory fibers on rat caudal nerve bundles. Results The Cummins method is sensitive to changes in motor and sensory fiber percentages in CVD if it is used with the volume conductor model. The Barker and Hirose methods are sensitive to motor fiber percentages in CVD but they cannot detect changes in sensory fiber percentages accurately. Conclusions Estimation of the CVD using a priori SFAP created with a volume conductor model can non-invasively supply accurate and precise information about fiber groups in a peripheral nerve bundle.

SPARC: A Hybrid Computational Approach to Classify Vagal C Fiber Functions

Neuroscience conventionally categorizes all unmyelinated fibers into an undifferentiated C fiber classification, implying a common function and impeding further classification. This is highly problematic, especially for autonomic nerves like the abdominal vagus, which contains >99% unmyelinated C fibers. We require a modern classification framework to discriminate differences among these important, underappreciated messengers. One important and easily measurable property of C fibers is their conduction speed, which relates directly to their morphology or caliber. We present a hybrid computational modeling approach, integrating biophysical (HH‐type) and classical (e.g., Gasser, Erlanger and Grundfest) methods, to enable the classification of C fiber function according to fiber caliber/speed.The Hybrid Nerve Response Modeling and Classification System is a tool to classify C fiber functions with respect to fiber caliber and radial location within a nerve. Biophysical models of HH axons contribute a bottom‐up model of fiber activation that explains the influence of the electrode configuration and other factors on fiber activation threshold and the measured compound action potential (CAP) profile. Alternatively, modeled CAPs can be generated through superposition of individual axon contributions (single fiber action potentials; SFAPs), relating fiber caliber distribution data to SFAP shape and conduction properties; this classical model of the CAP accurately predicts the experimentally measured maximal CAP shape. Using published and novel nerve ultrastructure data, we unified the biophysical and classical modeling approaches in a new simulation framework that predicts graded CAP profiles in response to bipolar, constant‐current stimuli delivered through various cuff electrode configurations.In this work, we demonstrate how the Hybrid Model can be used to discern the spatial and size distribution of unmyelinated C fibers from the CAP of the ventral gastric branch of the rat vagus nerve. Through our web‐based user interface (Fig. 1), we will show how our system can predict the activation threshold of unmyelinated fibers in any nerve cross section as a function of the individual fiber size and spatial location within a common set of electrode geometries. We will provide examples of how this information may be used to accelerate our delineation of the various functions of C fibers using measured associations between nerve and organ responses to stimulation.Support or Funding InformationFunding AcknowledgmentsThis work was supported by NIH SPARC OT2 OD023847 (PI: Powley), NIH SPARC OT2 OD025340 (PI: Grill) and NIH SPARC OT2 OD026585 01 (PI: Havton)[LEFT] Web‐based interface for the Hybrid Model. [FAR RIGHT] Segmented electron micrograph of n = 4776 C fibers from a rat ventral vagal gastric branch. The user interface lets users track the location (e.g., spatial location in the nerve cross section and temporal location in the CAP response) and relative activation thresholds of C fibers with respect to observed changes in the downstream physiology of the organs and tissues they supply.Figure 1

Feasibility of differentially measuring afferent and efferent neural activity with a single nerve cuff electrode

Objective. Advances in electrode technology have facilitated the development of neuroprostheses for restoring motor/sensory function in disabled individuals. Information extracted from a whole nerve, recorded using cuffs, can provide signals that control the operation of neuroprostheses. However, the amount of information that can be extracted from a tripolar cuff—which provides the highest signal-to-noise ratio (SNR)—is limited. The physical symmetry of the tripolar cuff results in neural recordings that cannot differentiate afferent versus efferent signals. In this study, we introduced a tetrapolar cuff to achieve low-noise and directionally sensitive recording. Approach. The tetrapolar cuff was initially designed using a computational approach. A finite element model was used to solve the electric potential generated at the electrode contacts by active electrical sources, such as the nodes of Ranvier and an artifact noise source. The resulting single fiber action potentials (SFAPs) and artifact noise signals (ANS) were used to characterize the performance of the tetrapolar configuration of the electrode length (EL) and electrode edge length (EEL) on simulated SFAP and ANS. The feasibility of using a tetrapolar cuff to differentiate afferent/efferent action potentials by applying potassium chloride in anesthetized rats was also investigated. Main results. Both the computational and experimental results of this study indicated that directional recording can be achieved using a tetrapolar cuff. Testing different design criteria (e.g. EL and EEL) showed that at EL values above 15 mm and EEL ⩾ 2 mm, the tetrapolar cuffs can yield larger SNRs than equally-sized tripolar cuffs. Significance. This study indicated that low-noise directionally sensitive measurement of neural activity can be achieved with a tetrapolar cuff. The experimental results confirmed the feasibility of using a tetrapolar cuff to differentiate afferent/efferent signals by applying potassium chloride. Further work is needed to determine whether the tetrapolar cuff can differentiate afferent/efferent physiologically elicited neural activities.

Symptom: Postauricular Mass

Symptom: Postauricular Mass

P33-S Does SFAP and jitter change when recorded from neuromuscular junction or near tendon in myopathy?

Background Neuromuscular jitter is measured 1–1.5 cm away from end-plate zone in order to record single fiber action potentials (SFAP) in near vicinity of neuromuscular junction (NMJ) where they are being generated. Recording the SFAPs also near to tendon may reflect the muscle fiber size and its variance that can be prominent in myopathies. This study aimed to define how properties of SFAP and jitter changes by moving the needle from neuromuscular junction to near to tendon in myopathic patients and to compare them with the ones recorded from healthy participants. Material and methods Three healthy participants and three patients with myopathy were enrolled. SFAPs were recorded during voluntary contraction with a disposable single-fiber EMG electrode and jitters were calculated in biceps brachi muscle at 2 sites: near NMJ and 5 cm distal. Measurements from different recording sites were performed at different sessions. The amplitude, rise time, the duration and peak duration of SFAPs were measured. Comparisons were done by using mixed ANOVA model. Results Moving the needle away from NMJ did not change the calculated parameters of SFAP and jitter in both groups. The only parameter which was significantly different in myopathy patients was slightly prolongation of both SFAP duration and the peak duration which was 0.78 ± 0.03 ms and 1.84 ± 0.06 ms in patients and 0.65 ± 0.04 ms and 1.49 ± 0.08 ms in healthy participants, respectively. Conclusions Longer duration of SFAP may reflect the poor conductance of muscle fibers as an indicator for small fiber size in myopathy.

P62-F Estimation of the muscle fiber diameter from single fiber potentials: A simulation study

Objective The aim of this study is to estimate the muscle fiber size variance relying on single fiber action potential features calculated near to end-plate zone and near to tendon in simulation models. Introduction Each muscle fiber generates Single Fiber Action Potential (SFAP). In neuromuscular disorders, diameter variance among the muscle fibers increases causing to temporal spreads in the EMG signal, especially if recorded at near tendon that can be used to estimate the fiber diameter. Materials and methods Two muscle fibers were created in EMG Simulator Program either with constant diameter or varying diameter between 20 and 90 microns. Different scenarios were built by varying the diameters. The generated SFAPs were recorded by a Single-Fiber EMG Electrode either close to end-plate or near-by the tendon. Temporal spreads computed by taking the difference of the duration between the minima of the signals measured from both recording sites were used to compute temporal fringing and the largest peak-to-peak amplitude through a MATLAB code. The varying fiber diameters were estimated by an Artificial Neural Network (ANN) system running Multilayer Perceptron (MLP) algorithm with inputs the constant fiber diameter, the largest peak-to-peak amplitude and the temporal fringing. Results The ANN system predicted the diameters of the second fibers with a-0.0823 relative mean error, a-3.9 mean absolute error and with a-11.83 maximum error. Discussion and conclusion The system can be accepted as successful although the performance of the system can be improved by presenting further features as input.

Serial Stimulated Jitter Analysis In Juvenile Myasthenia Gravis

Clinical and electrophysiological studies to measures disease activity in juvenile myasthenia gravis (JMG) are limited. Retrospective review of the clinical profile, Myasthenia Gravis Foundation of America (MGFA) scores, serial stimulated jitter analysis (Stim-JA) of the orbicularis oculi muscle, grip strength, and spirometry of patients with JMG who were followed in a multidisciplinary clinic was performed. Thirteen patients with JMG (9 females) with mean age of 13.2 ± 4.8 years and follow-up duration of 25.3 ± 8.3 months (range, 6-39) with ≥ 2 Stim-JA recordings were included. The mean jitter, mean percentage of apparent single-fiber action potentials (%ASFAP) with increased jitter, and mean %ASFAP with blocking at baseline values (77.3 ± 54.7 µs, 64.3% ± 35.8%, 39% ± 38.6%, respectively) and at follow-up (53 ± 45.4 µs, 51.2% ± 34.5%, 17% ± 29.4%, respectively) were abnormal; however, no statistically significant interval difference was noted. The electrophysiological data correlated significantly with Myasthenia Gravis Foundation of America (MGFA) class. Grip strength and spirometry did not correlate with MGFA class. Stimulated jitter values are sensitive biomarkers in JMG. Muscle Nerve 58: 729-732, 2018.