Estimation Of Conduction Velocity Research Articles

Effect of muscle‐fiber velocity recovery function on motor unit action potential properties in voluntary contractions

Measurements of muscle-fiber conduction velocity during voluntary contractions have been used in the diagnosis of neuromuscular diseases. However, the velocity of propagation of action potentials depends on the interspike interval of activation due to the velocity recovery function (VRF) of muscle fibers. The comparison of muscle-fiber conduction velocity estimates between individuals may thus be influenced by differences in motor unit discharge rate. This study investigates action potential properties of motor units of the sternocleidomastoid muscle during voluntary modulation of discharge rate with the purpose of assessing the effect of the VRF on motor unit properties in voluntary contractions. Nineteen healthy men trained to control a target motor unit with feedback of surface multichannel electromyographic (EMG) signals. The subjects performed three 30-s contractions of cervical flexion/rotation modulating the discharge rate of the target motor unit from 6.6 +/- 1.6 pps to 28.0 +/- 6.4 pps. Action potential conduction velocity was correlated to instantaneous discharge rate (R = 0.38 +/- 0.21). Action potential conduction velocity, peak-to-peak amplitude, and duration varied between minimum and maximum discharge rate (P < 0.01; percent change 12.3 +/- 5.0, -11.8 +/- 9.9, and -12.9 +/- 7.3). Thus, the properties of surface motor unit action potentials vary with modulation of discharge rate. This has implications for the use of conduction velocity values measured during voluntary contractions to differentiate patient populations from healthy individuals and for the development of normative data.

Estimation of muscle fiber conduction velocity of doublet discharges

A doublet is defined as two consecutive discharges of a motor unit occurring at short time interval between each other (e.g., <20 ms). In this paper, we propose a method for the estimation of muscle fiber conduction velocity (CV) from two partly overlapping action potentials generated by the same motor units. The method is based on the minimization of the mean square error between time-filtered versions of two surface EMG signals recorded along the direction of muscle fibers. The minimization is performed over the filter parameters that define the two propagation delays. The method was tested on simulated and experimental signals. Simulation results showed that the method is only in some cases superior to the simpler peak approach, due to limitations in the ideal model used for the algorithm development. However, application to experimental signals that mimic doublet motor unit discharges showed a substantial improvement in estimation quality of the new method with respect to the peak method.

Estimation of Muscle Fiber Conduction Velocity With a Spectral Multidip Approach

We propose a novel method for estimation of muscle fiber conduction velocity from surface electromyographic (EMG) signals. The method is based on the regression analysis between spatial and temporal frequencies of multiple dips introduced in the EMG power spectrum through the application of a set of spatial filters. This approach leads to a closed analytical expression of conduction velocity as a function of the auto- and cross-spectra of monopolar signals detected along the direction of muscle fibers. The performance of the algorithm was compared with respect to that of the classic single dip approach on simulated and experimental EMG signals. The standard deviation of conduction velocity estimates from simulated single motor unit action potentials was reduced from 1.51 m/s [10 dB signal-to-noise ratio (SNR)] and 1.06 m/s (20 dB SNR) with the single dip approach to 0.51 m/s (10 dB) and 0.23 m/s (20 dB) with the proposed method using 65 dips. When 200 active motor units were simulated in an interference EMG signal, standard deviation of conduction velocity decreased from 0.95 m/s (10 dB SNR) and 0.60 m/s (20 dB SNR) with a single dip to 0.21 m/s (10 dB) and 0.11 m/s (20 dB) with 65 dips. In experimental signals detected from the abductor pollicis brevis muscle, standard deviation of estimation decreased from (mean +/- SD over 5 subjects) 1.25 +/- 0.62 m/s with one dip to 0.10 +/- 0.03 m/s with 100 dips. The proposed method does not imply limitation in resolution of the estimated conduction velocity and does not require any iterative procedure for the estimate since it is based on a closed analytical formulation.

Estimation of muscle fiber conduction velocity from two-dimensional surface EMG recordings in dynamic tasks

The aims of this study are (1) to demonstrate that multi-channel surface electromyographic (EMG) signals can be detected with negligible artifacts during fast dynamic movements with an adhesive two-dimensional (2D) grid of 64 electrodes and (2) to propose a new method for the estimation of muscle fiber conduction velocity from short epochs of 2D EMG recordings during dynamic tasks. Surface EMG signals were collected from the biceps brachii muscle of four subjects with a grid of 13 × 5 electrodes during horizontal elbow flexion/extension movements (range 120–170°) at the maximum speed, repeated cyclically for 2 min. Action potentials propagating between the innervation zone and tendon regions could be detected during the dynamic task. A maximum likelihood method for conduction velocity estimation from the 2D grid using short time intervals was developed and applied to the experimental signals. The accuracy of conduction velocity estimation, assessed from the standard deviation of the residual of the regression line with respect to time, decreased from (range) 0.20–0.33 m/s using one column to 0.02–0.15 m/s when combining five columns of the electrode grid. This novel method for estimation of muscle fiber conduction velocity from 2D EMG recordings provides an estimate which is global in space and local in time, thus representative of the entire muscle yet able to track fast changes over the execution of a task, as is required for assessing muscle properties during fast movements.

Effect of electrode array position and subcutaneous tissue thickness on conduction velocity estimation in upper trapezius muscle

Muscle fiber conduction velocity (CV) was estimated in 20 healthy subjects with a multichannel technique using a linear electrode array placed on the upper trapezius (UT) muscle during isometric voluntary contractions at 20% of the maximal voluntary effort. The array had 16 contacts spaced by 5 mm and was centered in the middle of the line connecting C7 and the acromion. The effect of array displacement was investigated by shifting it either cranially or caudally by 1, 2 and 3 cm. The effect of array misalignment was investigated by rotating it either clockwise or counterclockwise, by 10°, 20° and 30°. The thickness of subcutaneous fat was measured by ultrasonic echography (range was 3–18 mm). The average location of the innervation zone of the UT is in the middle of the line connecting C7 to the acromion, however, individual differences of up to 2 cm were observed. The lateral side, near the acromion, should be preferred for electrode placement because of the thinner fat layer. The double differential (DD) montage should be preferred to the single differential (SD) electrode configuration. In this case, displacements of ±1 cm or misalignments of ±10° do not imply statistically significant bias in the estimate of CV. The same applies to amplitude and frequency variables estimated from the SD signals. CV estimates based on DD signals are lower because they are less affected by the thickness of the subcutaneous fat than estimates based on SD signals.

Design of Surface Electrode Array for Measuring Conduction Velocity in the Human Genioglossus Muscle

A new appliance, incorporating linear arrays of pin electrodes for genioglossus (GG) surface electromyography measurement, is presented. This design enables the estimation of GG muscle fiber conduction velocity, which decreases with fatigue. The performance of the device was evaluated for ten healthy human subjects during fatiguing and force varying contractions.

Simulation of Surface EMG Signals for a Multilayer Volume Conductor With Triangular Model of the Muscle Tissue

This study analytically describes surface electromyogram (sEMG) signals generated by a model of a triangular muscle, i.e., a muscle with fibers arranged in a fan shape. Examples of triangular muscles in the human body are the deltoid, the pectoralis major, the trapezius, the adductor pollicis. A model of triangular muscle is proposed. It is a sector of a cylindrical volume conductor (with the fibers directed along the radial coordinate) bounded at the muscle/fat interface. The muscle conductivity tensor reflects the fan anisotropy. Edge effects have been neglected. A solution of the nonspace invariant problem for a triangular muscle is provided in the Fourier domain. An approximate analytical solution for a two plane layer volume conductor model is obtained by introducing a homogeneous layer (modeling the fat) over the triangular muscle. The results are implemented in a complete sEMG generation model (including the finite length of the fibers), simulating single fiber action potentials. The model is not space invariant due to the changes of the volume conductor along the direction of action potential propagation. Thus the detected potentials at the skin surface change shape as they propagate. This determines problems in the extraction and interpretation of parameters. As a representative example of application of the simulation model, the influence of the inhomogeneity of the volume conductor in conduction velocity (CV) estimation is addressed (for two channels; maximum likelihood and reference point methods). Different fiber depths, electrode placements and small misalignments of the detection system with respect to the fiber have been simulated. The error in CV estimation is large when the depth of the fiber increases, when the detection system is not aligned with the fiber and close to the innervation point and to the tendons.

Estimation of average muscle fiber conduction velocity from simulated surface EMG in pinnate muscles

The aim of this simulation study was to assess the bias in estimating muscle fiber conduction velocity (CV) from surface electromyographic (EMG) signals in muscles with one and two pinnation angles. The volume conductor was a layered medium simulating anisotropic muscle tissue and isotropic homogeneous subcutaneous tissue. The muscle tissue was homogeneous for one pinnation angle and inhomogeneous for bipinnate muscles (two fiber directions). Interference EMG signals were obtained by simulating recruitment thresholds and discharge patterns of a set of 100 and 200 motor units for the pinnate and bipinnate muscle, respectively (15 degrees pinnation angel in both cases). Without subcutaneous layer and muscle fibers with CV 4m/s, average CV estimates from the pinnate (bipinnate) muscle were 4.81+/-0.18 m/s (4.80+/-0.18 m/s) for bipolar, 4.71+/-0.19 m/s (4.71+/-0.12 m/s) for double differential, and 4.78+/-0.16 m/s (4.79+/-0.15m/s) for Laplacian recordings. When subcutaneous layer was added (thickness 1mm) in the same conditions, estimated CV values were 4.93+/-0.25 m/s (5.16+/-0.41 m/s), 4.70+/-0.21 m/s (4.83+/-0.33 m/s), and 4.89+/-0.21 m/s (4.99+/-0.39 m/s), for the three recording systems, respectively. The main factor biasing CV estimates was the propagation of action potentials in the two directions which influenced the recording due to the scatter of the projection of end-plate and tendon locations along the fiber direction, as a consequence of pinnation. The same problem arises in muscles with the line of innervation zone locations not perpendicular to fiber direction. These results indicate an important limitation in reliability of CV estimates from the interference EMG when the innervation zone and tendon locations are not distributed perpendicular to fiber direction.

Estimation of Motor Unit Conduction Velocity From Surface EMG Recordings by Signal-Based Selection of the Spatial Filters

Muscle fiber conduction velocity (CV) can be estimated by the application of a pair of spatial filters to surface electromagnetic (EMG) signals and compensation of the spatial filter transfer function with equivalent temporal filters. This method integrates the selection of the spatial filters for signal detection to the estimation of CV. Using this approach, in this paper, we propose a novel technique for signal-based selection of the spatial filter pair that minimizes the effect of nonpropagating signal components (end-of-fiber effects) on CV estimates (optimal filters). The technique is applicable to signals with one propagating and one nonpropagating component, such as single motor unit action potentials. It is shown that the determination of the optimal filters also allows the identification of the propagating and nonpropagating signal components. The new method was applied to simulated and experimental EMG signals. Simulated signals were generated by a cylindrical, layered volume conductor model. Experimental signals were recorded from the abductor pollicis brevis with a linear array of 16 electrodes. In the simulations, the proposed approach provided CV estimates with lower bias due to nonpropagating signal components than previously proposed methods based on the entire signal waveform. In the experimental signals, the technique separated propagating and nonpropagating signal components with an average reconstruction error of 2.9 +/- 0.9% of the signal energy. The technique may find application in single motor unit studies for decreasing the variability and bias of CV estimates due to the presence and different weights of the nonpropagating components.

P15.26 Estimation of motor conduction velocity with radial nerve neuropathy in spiral groove using nerve conduction studies

P15.26 Estimation of motor conduction velocity with radial nerve neuropathy in spiral groove using nerve conduction studies

Interpretation of the Surface Electromyogram in Dynamic Contractions

This review focuses on methods for extracting information from the surface EMG recorded in dynamic contractions. It examines the techniques, requirements, and limitations associated with detecting the timing of muscle activation, assessing the modulation of signal amplitude, performing EMG spectral analysis, and estimating conduction velocity. The conclusion is that interpretation of the surface EMG in dynamic tasks requires caution.

Impulse propagation in late-stage embryonic and neonatal murine ventricular slices

Aim To evaluate whether field potential recordings from murine ventricular slice preparations serve as a model to investigate impulse propagation. Method Late-stage embryonic and neonatal murine hearts were sliced by a vibratome. Slices were placed on planar microelectrode arrays (MEAs). Field potentials of spontaneously beating and electrically stimulated contractions were recorded. The maximal negative deflection of the field potentials (dV / dt) was calculated to assess the local activation time, to create activation sequence maps, and to estimate conduction velocity. Results Mapping of impulse propagation of late-stage embryonic and neonatal murine ventricular slices and estimation of conduction velocities is feasible using the MEA technique showing an impulse propagation reflecting anatomical structures and conduction velocities similar to those obtained with other techniques. Conclusion The combination of viable ventricular slice preparations with the MEA technique offers a versatile and powerful technique to study cardiac impulse propagation.

Errata

The Journal of PhysiologyVolume 573, Issue 1 p. 283-283 Free Access Errata This article corrects the following: Non-uniform olivocerebellar conduction time in the vermis of the rat cerebellum M. R. Baker, S. A. Edgley, Volume 570Issue 3The Journal of Physiology pages: 501-506 First Published online: January 16, 2006 First published: 09 May 2006 https://doi.org/10.1113/jphysiol.2006.571103AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat The paper by Baker & Edgley contains a number of errors. On spage 505, Fig. 4 should have appeared as follows. Figure 4Open in figure viewerPowerPoint Depth–latency relationships: grouped data The scatterplot shows latencies of CF reflex responses against depth of recording. There is a significant relationship: the depth of the recorded unit was significantly predictive of the latency of the recorded unit (t-statistic, P < 0.001; F= 11.7, P < 0.002). Least squares regression analysis revealed an inverse relationship (y= 8.45 − 1.456x). The continuous line through the data points represents the least squares regression; the dashed lines delimit the prediction interval and the 95% confidence interval (n= 33). These data were obtained from 11 different experiments, which may explain some of the variation in latency at each depth. There is an error on pages 501 and 505: the estimates of conduction velocity given in the text (0.6 m s−1) should read 0.7 m s−1. On page 505, in column 2 the last sentence of the second paragraph should have read: ‘Therefore considering a range of latencies of between 3 and 5 ms for conduction between inferior olive and cerebellar cortex for the rat (estimated from the means and standard deviaitons quoted by Sugihara et al. 1993), a range of approximately 6–10 ms for CF reflex evoked responses could be expected’. The authors regret these errors. References Baker MR & Edgley SA (2006). Non-uniform olivocerebellar conduction time in the vermis of the rat cerebellum. J Physiol 570, 501– 506. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Volume573, Issue1May 2006Pages 283-283 FiguresReferencesRelatedInformation

AB38-1: Regional ventricular conduction velocity substrate mapping in patients with ventricular tachycardia after myocardial infarction

Substrate mapping to guide ventricular tachycardia (VT) ablation after myocardial infarction (MI) utilizes bipolar voltage maps, but additional methods are needed to refine the location of reentry circuit regions in large infarcts. Slow conduction is an important component of the reentry substrate. A recently developed algorithm calculates an estimate of regional conduction velocity (ERCV) from electroanatomic maps by creating a dominant wave-front propagation vector from adjacent activation times (Coperniqs).

Spatial and temporal changes of upper trapezius muscle fiber conduction velocity are not predicted by surface EMG spectral analysis during a dynamic upper limb task

The purpose of the study was to examine the temporal and spatial correlation between estimates of trapezius muscle fiber conduction velocity (CV) and surface EMG instantaneous mean power spectral frequency (iMPF) during dynamic movement of the upper limb. Surface EMG signals were detected from the upper division of the trapezius muscle in 13 healthy volunteers using linear arrays of eight electrodes at three locations in the cephalad–caudal direction. Subjects were asked to tap with their hands in a cyclic manner between targets positioned mid thigh and 120° of shoulder flexion, to the beat of a metronome set at 88 beats per minute for 5 min. Muscle fiber CV and iMPF were estimated for each cycle at the time instant corresponding to 90° of shoulder flexion. Non-significant correlations were identified between CV and iMPF initial values ( R 2 = 0.03–0.01), rate of change over time ( R 2 = 0.10–0.004) and normalized rate of change ( R 2 = 0.12–0.01) at all three locations on the upper trapezius muscle. These results demonstrate that both spatial and temporal variations in trapezius muscle fiber CV are not predicted by EMG spectral analysis during dynamic movement of the upper limb. This finding suggests that spectral analysis cannot be used to infer changes in the spatial and temporal behavior of muscle fiber CV during dynamic tasks.

Spinal force estimation from non-normalized EMG

We propose a novel method for the estimation of muscle fiber conduction velocity (CV) from surface EMG recordings. The approach is based on the analysis of signals detected along a number of linear electrode arrays parallel to the fiber direction, thus collected by a bi-dimensional (2-D) array (matrix) of electrodes. The information provided by the 2-D array is used to derive a maximum likelihood estimator which can be applied to any number of signals and which may account for missing channels in the matrix. An iterative technique in the frequency domain for the estimation of the propagation delay is proposed to reduce the computational time and avoid the limit of resolution due to signal sampling. The method proposed is applied to signals collected from the biceps brachii muscle of eight healthy subjects during isometric, constant force contractions at 50% of the maximal voluntary contraction torque. It is shown that CV estimation standard deviation and sensitivity to electrode displacements significantly decrease by the application of the method proposed with respect to classic CV estimation techniques. The method promises to be a useful tool when average CV is estimated for muscle assessment and diagnostic purposes.

Neuromuscular assessment in elderly workers with and without work related shoulder/neck trouble: the NEW-study design and physiological findings

Musculoskeletal disorders in the neck and shoulder area are a major occupational concern in the European countries especially among elderly females. The aim was to assess these disorders based on quantitative EMG indicators and functional tests. 252 female computer users (45-68 years) were recruited from four European countries in two contrast groups: (1) 88 neck/shoulder (NS) cases reporting trouble in the neck and/or shoulder region for more than 30 days during the last year, and (2) 164 NS-controls reporting such trouble for no more than 7 days. Questionnaires, functional/clinical tests, and physiological recordings were performed in workplace related field studies. The results showed no differences in anthropometrics but NS-cases reported more strained head positions and more eye problems than controls. The psychosocial working factors were similar, although, NS-controls had slightly better scores on working conditions, general health, and vitality compared to cases. The NS-cases had lower maximal voluntary contraction (MVC) during shoulder elevation (mean (SD) 310 (122) N) compared to the controls (364 (122) N). During 30% MVC electromyography (EMGrms) in the trapezius muscle was lower in NS-cases (194 (105) muV) than in controls (256 (169) muV), while no differences were found regarding endurance time. Estimated conduction velocity was not different between NS-cases and -controls. Four functional computer tests were performed equally well by NS-cases and -controls, and the corresponding EMG variables also did not differ. A major finding in this large-scale epidemiological study is the significantly lower MVC in NS-cases compared with NS-controls together with lower EMGrms value at 30% MVC, while computer tasks were performed at similar relative muscle activation. The study was unable to reveal quantitative EMG indicators and functional tests that could objectively assess disorders in NS-cases.

Tracking motor unit action potentials in the tibialis anterior during fatigue

New surface electromyogram (SEMG) techniques offer the potential to advance knowledge of healthy and diseased motor units. Conduction velocity (CV) estimates, obtained from indwelling electrodes, may provide diagnostic information, but the standard method of CV estimation from SEMG may be of only limited value. We developed a motor unit (MU) tracking algorithm to extract motor unit conduction velocity (MUCV) and motor unit action potential (MUAP) amplitude estimates from SEMG. The technique is designed to provide a noninvasive means of accessing fatigue and recruitment behavior of individual MUs. We have applied this MU tracking algorithm to SEMG data recorded during isometric fatiguing contractions of the tibialis anterior (TA) muscle in nine healthy subjects, at 30%-40% maximum voluntary contraction (MVC). The results reveal that MUCVs and MUAP amplitudes of individual MUs can be estimated and tracked across time. Time-related changes in the MU population may also be monitored. Thus, the SEMG technique employed provides insight into the behavior of the underlying muscle at the MU level by noninvasive means.

Balance control in peripheral neuropathy: Are patients equally unstable under static and dynamic conditions?

The aim of this investigation was to assess the potentially different effects of impaired proprioceptive input in balance control under static and dynamic conditions in neuropathic patients. We recruited 20 normal subjects and 27 patients affected by neuropathies known to affect to a different extent large and medium size afferent fibres. The patients comprised 5 with Charcot-Marie-Tooth disease type 1A (CMT1A), 8 with CMT type 2 (CMT2) and 14 with Diabetes polyneuropathy (Diabetics). Measurement of balance during quiet stance on a stabilometric platform showed that sway area (SA) was larger in the CMT2 and Diabetics than normal subjects or in CMT1A, under both eyes open and closed conditions. The estimated conduction velocity (CV) of the group II afferent fibres was lower in CMT2 and Diabetics than in normal subjects and CMT1A. Across all patients, SA increased as a function of the slowing of group II CV. During a dynamic balance task the head A-P displacement was only slightly increased in the patient groups with respect to normals, despite the increased delay at which the head followed displacement of the feet. The unpredictably good performance of all patient groups under dynamic condition, which was at variance with their imbalance during quiet stance, may indicate that these patients learnt to exploit anticipatory postural strategies.

Simultaneous estimation of muscle fibre conduction velocity and muscle fibre orientation using 2D multichannel surface electromyogram

The paper presents a new approach for simultaneous estimation of muscle fibre conduction velocity (MFCV) and muscle fibre orientation (MFO) for motor units (MUs) in two-dimensional (2D) multichannel surface electromyography recordings. This is an important tool for detecting changes and abnormalities in muscle function and structure. In addition, simultaneous estimation of MFO and MFCV avoids the necessity of manual electrode alignment. The proposed method detected propagating MU action potentials (MUAPs) in a running time window as moving components in amplitude maps. Thereafter, estimations were obtained by fitting a three-dimensional function to these maps. The performance was evaluated using synthetic MU signals at 10 dB SNR and authentic biceps brachii measurements. Results demonstrated MFCV and MFO estimates with standard deviations of less than 0.05 m s(-1) and 1 degrees for simulated signals, and less than 0.2 m s(-1) and 4 degrees for experimental data. However, standard deviations as low as 0.12 m s(-1) and 1.6 degrees from real signals were demonstrated. It was concluded that the method performs as well as, or better than, linear array multichannel methods when individual propagating MUAPs can be identified, even if electrodes are not aligned with fibre direction.