Conduction Velocity Distribution Research Articles

Distribution of muscle fibre conduction velocity for representative samples of motor units in the full recruitment range of the tibialis anterior muscle.

Motor units are recruited in an orderly manner according to the size of motor neurones. Moreover, because larger motor neurones innervate fibres with larger diameters than smaller motor neurones, motor units should be recruited orderly according to their conduction velocity (MUCV). Because of technical limitations, these relations have been previously tested either indirectly or in small motor unit samples that revealed weak associations between motor unit recruitment threshold (RT) and MUCV. Here, we analyse the relation between MUCV and RT for large samples of motor units. Ten healthy volunteers completed a series of isometric ankle dorsiflexions at forces up to 70% of the maximum. Multi-channel surface electromyographic signals recorded from the tibialis anterior muscle were decomposed into single motor unit action potentials, from which the corresponding motor unit RT, MUCV and action potential amplitude were estimated. Established relations between muscle fibre diameter and CV were used to estimate the fibre size. Within individual subjects, the distributions of MUCV and fibre diameters were unimodal and did not show distinct populations. MUCV was strongly correlated with RT (mean (SD) R2 =0.7 (0.09), P<0.001; 406 motor units), which supported the hypothesis that fibre diameter is associated with RT. The results provide further evidence for the relations between motor neurone and muscle fibre properties for large samples of motor units. The proposed methodology for motor unit analysis has also the potential to open new perspectives in the study of chronic and acute neuromuscular adaptations to ageing, training and pathology.

Is peripheral paraneoplastic neurological syndrome possible in primary brain tumors?

IntroductionSystemic malignant diseases cause the induction of autoimmunity, for example, paraneoplastic syndromes. There are no proofs of paraneoplastic syndromes in primary brain tumors. The aim of the study was to evaluate the involvement of the peripheral nervous system, together with an assessment of onconeuronal and antineural antibodies as indicators of humoral immune response against nervous system in patients with primary brain tumors.Materials and MethodsClinical examinations, electrophysiological studies of peripheral nerves (motor and sensory conduction velocity studies, conduction velocity distribution tests, thermal and vibratory quantitative sensory tests, and sympathetic skin response tests) and muscles, blood sampling collection (assessment of onconeuronal, and antineural antibodies) were performed on 33 patients with newly recognized primary brain tumors within 2–4 days after their admission to our department.ResultsWe revealed statistically significant changes of peripheral nerves, more pronounced in the peroneal nerve in standard and conduction velocity distribution tests, as well as in sympathetic skin responses. We revealed significantly higher vibratory thresholds, and pain thresholds for cold and warm in the upper and lower limbs in the study group than in the controls. In five patients, we have identified anti‐neuroendothelium, anti‐GFAP, anti‐MAG, anti‐PCNA, and anti‐Ro52 antibodies.ConclusionsIn patients with primary brain tumors, electrophysiological changes in peripheral nerves, together with the presence of the antineural antibodies suggest an autoimmune humoral response, and make the diagnosis of paraneoplastic neurological syndrome possible.

Distribution of Conduction Velocity (DCV) from measured F-Wave Latency for detection of cervical spondylotic radiculopathy and myelopathy (CRM)

In the previous work of our extended group at Dhaka, Distribution of Conduction Velocity (DCV) of motor nerve fibres in a peripheral nerve trunk was established as an approximate mirror image of Distribution of F-Latency (DFL), for which consecutive 30 to 40 F-latencies were used through multiple stimulation of a peripheral nerve trunk. Using patterns of DFL a considerable amount of experience has been built up in the detection of Cervical Spondylotic Radiculopathy and Myelopathy (CRM). In the present work we have obtained DCV directly from the Conduction Velocity (CV) values obtained from each of the F-latencies. Because of the inverse relationship between latency and velocity, a small variation to the mirror image should be present, particularly when discrete bin widths are used to obtain the frequency distribution. Therefore, one challenge was to choose an appropriate bin width while obtaining DCV directly so that the patterns can be related to those of DFL easily for the detection of CRM. To obtain DFL our extended group at Dhaka had used a bin width of 2 ms which gave good results. To choose a corresponding bin width for DCV four recognized measures of central tendency: Average of the range, Median, Mode and Mean (weighted average) were used and the resulting patterns of DCV were compared to that of DFL to determine the percentage of matches with respect to the detection of CRM. It was observed that Median gave the best DCV with 89% matches followed closely by Mode giving 83% match. The other two gave much lower values, 67% and 50%. Therefore, median value gave the best match which could be used to obtain DCV from the CV values directly, for the determination of CRM.Bangladesh Journal of Medical Physics Vol.7 No.1 2014 56-65

Dexmedetomidine augments the effect of lidocaine: power spectrum and nerve conduction velocity distribution study.

BackgroundIn this study, the individual and combined inhibitory effects of dexmedetomidine and lidocaine on the conduction group of isolated nerve were investigated by determining conduction velocity distribution (CVD) and power spectrum.MethodsElectrophysiological compound action potential (CAP) recordings were conducted on isolated rat sciatic nerve before (Con) and 20 minutes after exposure to 1 mM lidocaine (Lido), 21pM dexmedetomidine (Dex) and their combination (Lido + Dex). Then for CVD, mathematical model and for power spectrum Fast Fourier analysis were conducted.ResultsDexmedetomidine alone made no significant difference in shape and duration of CAPs as compared to Con, on the other hand lidocaine depresses amplitude and prolongs the duration of CAPs, but not more than combination of dexmedetomidine and lidocaine can do.Lidocaine caused a shift in the CVD histogram to relatively slower conducting group significantly while dexmedetomidine did not cause any significant change as compared to Control. Lidocaine, when combined with dexmedetomidine revealed a remarkable effect on the whole CVD histogram by causing almost complete blockage of fast conducting nerve fibers. The relative number of fibers in CVD is conserved for separate applications of anesthetics, but not for their combination.As in CVD, power spectrum shifted from higher to lower frequency region by lidocaine and significantly for lidocaine combined with dexmedetomidine application. Shifts for dexmedetomidine applied group were seen beggarly.ConclusionsWe have concluded that dexmedetomidine alone did not influence nerve conduction, but when it is used with lidocaine it augments neural conduction blockage effect, especially on fast conducting nerve fibers.

Alternative Paradigm of Selective Vagus Nerve Stimulation Tested on an Isolated Porcine Vagus Nerve

Alternative paradigm for spatial and fibre-type selective vagus nerve stimulation (VNS) was developed using realistic structural topography and tested in an isolated segment of a porcine cervical left vagus nerve (LVN). A spiral cuff (cuff) containing a matrix of ninety-nine electrodes was developed for selective VNS. A quasitrapezoidal stimulating pulse (stimulus) was applied to the LVN via an appointed group of three electrodes (triplet). The triplet and stimulus were configured to predominantly stimulate the B-fibres, minimizing stimulation of the A-fibres and by-passing the stimulation of the C-fibres. To assess which fibres made the most probable contribution to the neural response (NR) during selective VNS, the distribution of conduction velocity (CV) within the LVN was considered. Experimental testing of the paradigm showed the existence of certain parameters and waveforms of the stimulus, for which the contribution of the A-fibres to the NR was slightly reduced and that of the B-fibres was slightly enlarged. The cuff provided satisfactory fascicle discrimination in selective VNS as well as satisfactory fascicle discrimination during NR recording. However, in the present stage of development, fibre-type VNS remained rather limited.

Hypothesis to Explain the Occurrence of Multiple Peaks of DFL in Nerve Conduction Measurement

Distribution of F-Latency (DFL) is a new nerve conduction parameter obtained using evoked EMG responses, and was introduced by us earlier. We had established that DFL is simply related to the distribution of conduction velocity (DCV) of motor fibres in a peripheral nerve, as an approximate mirror image. Normally DFL has a single peak for healthy nerves, but double, or sometimes, triple peaks of DFL were observed in the median nerve, recording the evoked EMG responses from the Thenar muscle in the palm of the hand. From observation, we also established that such multiple peaks of DFL are associated with Cervical Spondylosis (CS). Double peaks were also observed on the nerves of legs suggesting association with Lumbo-sacral spondylotic neuropathy. The present work puts forward hypotheses to explain the occurrence of double or triple peaks of DFL from median nerve in CS, based on principles of physics, physiology and mathematics, and relate these to observations. This includes observations reported in our earlier work, and also obtained from hundreds of patients tested at a clinic managed by the author. The hypothesis assumes similar DCV with single peaks for all the nerve branches that combine to form the median nerve. Compression or degeneation of one or two of the above nerve branches will result in differential shifts of DFLs, and therefore a combination in the median nerve will give rise to double or triple peaks. Initially the explanation was based on radiculopathy, but the hypotheses evolved when newer neuropathological conditions like myelopathy, and external nerve injury were observed. Finally a generalized hypothesis has been put forward that would cover all these abnormal conditions that affect a peripheral nerve of a limb, both in the hands and the legs. Experiments have been suggested that may test these hypotheses, which, if successful, will lead to a greater understanding of neurophysiology and provide a simple and sensitive diagnostic test through the use of DFL. DOI: http://dx.doi.org/10.3329/bjmp.v4i1.14675 Bangladesh Journal of Medical Physics Vol.4 No.1 2011 27-36

The latency distribution of motor evoked potentials in patients with multiple sclerosis

ObjectiveTo compare the individual latency distributions of motor evoked potentials (MEP) in patients with multiple sclerosis (MS) to the previously reported results in healthy subjects (Firmin et al., 2011). MethodsWe applied the previously reported method to measure the distribution of MEP latencies to 16 patients with MS. The method is based on transcranial magnetic stimulation and consists of a combination of the triple stimulation technique with a method originally developed to measure conduction velocity distributions in peripheral nerves. ResultsMEP latency distributions in MS typically showed two peaks. The individual MEP latency distributions were significantly wider in patients with MS than in healthy subjects. The mean triple stimulation delay extension at the 75% quantile, a proxy for MEP latency distribution width, was 7.3ms in healthy subjects and 10.7ms in patients with MS. ConclusionsIn patients with MS, slow portions of the central motor pathway contribute more to the MEP than in healthy subjects. The bimodal distribution found in healthy subjects is preserved in MS. SignificanceOur method to measure the distribution of MEP latencies is suitable to detect alterations in the relative contribution of corticospinal tract portions with long MEP latencies to motor conduction.

Axonal Transmission in the Retina Introduces a Small Dispersion of Relative Timing in the Ganglion Cell Population Response

BackgroundVisual stimuli elicit action potentials in tens of different retinal ganglion cells. Each ganglion cell type responds with a different latency to a given stimulus, thus transforming the high-dimensional input into a temporal neural code. The timing of the first spikes between different retinal projection neurons cells may further change along axonal transmission. The purpose of this study is to investigate if intraretinal conduction velocity leads to a synchronization or dispersion of the population signal leaving the eye.Methodology/Principal FindingsWe ‘imaged’ the initiation and transmission of light-evoked action potentials along individual axons in the rabbit retina at micron-scale resolution using a high-density multi-transistor array. We measured unimodal conduction velocity distributions (1.3±0.3 m/sec, mean ± SD) for axonal populations at all retinal eccentricities with the exception of the central part that contains myelinated axons. The velocity variance within each piece of retina is caused by ganglion cell types that show narrower and slightly different average velocity tuning. Ganglion cells of the same type respond with similar latency to spatially homogenous stimuli and conduct with similar velocity. For ganglion cells of different type intraretinal conduction velocity and response latency to flashed stimuli are negatively correlated, indicating that differences in first spike timing increase (up to 10 msec). Similarly, the analysis of pair-wise correlated activity in response to white-noise stimuli reveals that conduction velocity and response latency are negatively correlated.Conclusion/SignificanceIntraretinal conduction does not change the relative spike timing between ganglion cells of the same type but increases spike timing differences among ganglion cells of different type. The fastest retinal ganglion cells therefore act as indicators of new stimuli for postsynaptic neurons. The intraretinal dispersion of the population activity will not be compensated by variability in extraretinal conduction times, estimated from data in the literature.

An early diagnostic tool for diabetic neuropathy: Conduction velocity distribution

Diabetes is a metabolic disorder that affects much of the human population. As a secondary complication, diabetic neuropathy causes time-dependent damage to peripheral nerves. In this study, experimental diabetes was induced by streptozotocin (STZ; 50 mg/kg intraperitoneally) in rats. Diabetic animals were grouped into those with 2 or 4 weeks of diabetes, whereas a control group received only the STZ vehicle (0.1 M citrate). Sciatic nerves were dissected, and compound action potentials (CAPs) were recorded. Results deduced by conventional calculation carried less information when compared with conduction velocity distribution (CVD) obtained by a computer-based mathematical model. Using the conventional approach, statistically significant changes were first seen in the fourth week of diabetes, whereas results deduced by CVD measurement could be seen in the second week. Consequently, the CVD calculation provides more information for the early diagnosis of neuropathies compared with classical conduction velocity measurements.

Acute Atrial Dilatation Slows Conduction and Increases AF Vulnerability in the Human Atrium

The mechanisms by which atrial stretch favors the development of a substrate for atrial fibrillation (AF) are not fully understood. In this study, the role of stretch-induced conduction changes in the creation of a proarrhythmic substrate has been investigated by quantifying the spatial distribution of local conduction velocities (CVs) in the human atrium during acute atrial dilatation. Electroanatomic mapping of right atrial activation was performed in 10 patients during coronary sinus pacing under control condition and during acute atrial dilatation. Atrial stretch was obtained by simultaneous atrioventricular (AV) pacing at a cycle length of 450-500 ms. Local CVs were accurately estimated by applying the principle of triangulation and spatially mapped over the whole right atrial endocardial surface. Simultaneous AV pacing significantly increased right atrial volume from 72.0 ± 29.0 to 86.3 ± 31.3 mL (P < 0.001). The 23% increase in atrial volume resulted in an overall decrease in atrial CV from 65.8 ± 5.9 to 55.2 ± 7.2 cm/s (P < 0.001) and an increased incidence of slow conduction sites or local conduction blocks from 10.3 ± 4.2% to 15.9 ± 7.7% (P < 0.01). Acute atrial dilatation concurrently increased AF vulnerability, with 6 of 10 patients developing AF episodes under stretch condition. Quantification of stretch-induced conduction changes in the human atrium is feasible by combining simultaneous AV pacing and CV map construction. Acute atrial dilatation results in conduction slowing and significant increase in AF vulnerability, suggesting the role of stretch-induced conduction disturbances in the creation of a substrate for AF.

Comparative Effects of Alpha Lipoic Acid and Melatonin on Cisplatin-Induced Neurotoxicity

ABSTRACTCisplatin is a carcinogenic agent having important cytotoxic effects. Cisplatin treatment increases the levels of free oxygen radicals in neurologic tissues. We investigated the effects of alpha lipoic acid (ALA) and melatonin (MEL) on the electrophysiological parameters and on activities of nerve fibers having different conduction properties on cisplatin neurotoxicity. Neurotoxicity was induced by a single injection of 10 mg/kg intraperitoneal (ip) cisplatin. Supplementation was started 1 day before cisplatin injection with either 100 mg/kg/day ip ALA or 4 mg/kg/day ip MEL for 7 days. Compound action potentials were recorded from isolated sciatic nerves in vitro, and numerical analyses were conducted. Cisplatin-induced neurotoxicity resulted in a significant decrease (p <.05) in maximum depolarization (mV), areas (mV·ms), and maximum and minimum upstroke velocity values (mV/ms). Although these decrements were restored by ALA and MEL, ALA was found to be more effective. Conventional conduction velocity measurements and conduction velocity distribution histograms have shown that ALA supplementation can recover the effects of cisplatin while MEL cannot. The conduction velocity distribution histograms have shown that antioxidant supplementation results in a restoration on contribution of fast-conducting fibers (51.8–77.7 m/s), which is deteriorated by cisplatin. Consequently, ALA has more potential to make up for the deleterious effects of cisplatin-induced neurotoxicity.

The rat caudal nerves: a model for experimental neuropathies

This study provides a detailed investigation of the anatomy of the rat caudal nerve along its entire length, as well as correlated nerve conduction measures in both large and small diameter axons. It determines that rodent caudal nerves provide a simple, sensitive experimental model for evaluation of the pathophysiology of degeneration, recovery, and prevention of length-dependent distal axonopathy. After first defining the normal anatomy and electrophysiology of the rat caudal nerves, acrylamide monomer, a reliable axonal toxin, was administered at different doses for escalating time periods. Serial electrophysiological recordings were obtained, during intoxication, from multiple sites along caudal and distal sciatic nerves. Multiple sections of the caudal and sciatic nerves were examined with light and electron microscopy. The normal distribution of conduction velocities was determined and acrylamide-induced time- and dose-related slowing of velocities at the vulnerable ultraterminal region was documented. Degenerative morphological changes in the distal regions of the caudal nerves appeared well before changes in the distal sciatic nerves. Our study has shown that (1) rat caudal nerves have a complex neural structure that varies along a distal-to-proximal gradient and (2) correlative assessment of both morphology and electrophysiology of rat caudal nerves is easily achieved and provides a highly sensitive index of the onset and progression of the length-dependent distal axonopathy.

Possible detection of cervical spondylotic neuropathy using Distribution of F-latency (DFL), a new neurophysiological parameter

BackgroundWe have previously reported a new nerve conduction measurement parameter which we named the Distribution of F-latency (DFL) and showed that this was an approximate mirror of the Distribution of Conduction Velocity (DCV) of motor nerve fibers. This work was performed using measurements on the 20 median nerves from 10 volunteers. The DFL showed a number of different patterns including single peaks, broad peaks and double peaks, the latter observed on subjects with Cervical Spondylosis (CS). It was thought that a retrospective analysis of these data could be worthwhile in determining whether Cervical Spondylotic neuropathy could be detected using the DFL.FindingsThe DFL from the 8 median nerves of 4 normal subjects had single peaks, which has been assumed to represent a normal pattern. The DFL from one side of 5 subjects diagnosed with or suspected to have CS had double peaks. Broad peaks were observed in 7 nerves of which 5 were from subjects who had double peaks in the DFL on the contra lateral side.ConclusionsBased on these findings, double peaks in the DFL appear to be associated with CS neuropathy. These findings further suggest that broad peaks in the DFL could indicate the early stages of the disease. Differential compression of nerve branches at the spinal roots are being explored as possible causes. This study does not preclude other pathologies contributing to double or broad peaks, but does suggest that the DFL could form a screening tool for CS neuropathy.

Magnetic measurements of peripheral nerve function using a neuromagnetic current probe

The progress made during the last three decades in mathematical modeling and technology development for the recording of magnetic fields associated with cellular current flow in biological tissues has provided a means of examining action currents more accurately than that of using traditional electrical recordings. It is well known to the biomedical research community that the room-temperature miniature toroidal pickup coil called the neuromagnetic current probe can be employed to measure biologically generated magnetic fields in nerve and muscle fibers. In contrast to the magnetic resonance imaging technique, which relies on the interaction between an externally applied magnetic field and the magnetic properties of individual atomic nuclei, this device, along with its room-temperature, low-noise amplifier, can detect currents in the nano-Ampere range. The recorded magnetic signals using neuromagnetic current probes are relatively insensitive to muscle movement since these probes are not directly connected to the tissue, and distortions of the recorded data due to changes in the electrochemical interface between the probes and the tissue are minimal. Contrary to the methods used in electric recordings, these probes can be employed to measure action currents of tissues while they are lying in their own natural settings or in saline baths, thereby reducing the risk associated with elevating and drying the tissue in the air during experiments. This review primarily describes the investigations performed on peripheral nerves using the neuromagnetic current probe. Since there are relatively few publications on these topics, a comprehensive review of the field is given. First, magnetic field measurements of isolated nerve axons and muscle fibers are described. One of the important applications of the neuromagnetic current probe to the intraoperative assessment of damaged and reconstructed nerve bundles is summarized. The magnetic signals of crushed nerve axons and the determination of the conduction velocity distribution of nerve bundles are also reviewed. Finally, the capabilities and limitations of the probe and the magnetic recordings are discussed.

Axonal Velocity Distributions in Neural Field Equations

By modelling the average activity of large neuronal populations, continuum mean field models (MFMs) have become an increasingly important theoretical tool for understanding the emergent activity of cortical tissue. In order to be computationally tractable, long-range propagation of activity in MFMs is often approximated with partial differential equations (PDEs). However, PDE approximations in current use correspond to underlying axonal velocity distributions incompatible with experimental measurements. In order to rectify this deficiency, we here introduce novel propagation PDEs that give rise to smooth unimodal distributions of axonal conduction velocities. We also argue that velocities estimated from fibre diameters in slice and from latency measurements, respectively, relate quite differently to such distributions, a significant point for any phenomenological description. Our PDEs are then successfully fit to fibre diameter data from human corpus callosum and rat subcortical white matter. This allows for the first time to simulate long-range conduction in the mammalian brain with realistic, convenient PDEs. Furthermore, the obtained results suggest that the propagation of activity in rat and human differs significantly beyond mere scaling. The dynamical consequences of our new formulation are investigated in the context of a well known neural field model. On the basis of Turing instability analyses, we conclude that pattern formation is more easily initiated using our more realistic propagator. By increasing characteristic conduction velocities, a smooth transition can occur from self-sustaining bulk oscillations to travelling waves of various wavelengths, which may influence axonal growth during development. Our analytic results are also corroborated numerically using simulations on a large spatial grid. Thus we provide here a comprehensive analysis of empirically constrained activity propagation in the context of MFMs, which will allow more realistic studies of mammalian brain activity in the future.

Mechanosensitive Primary Bladder Afferent Activity in Rats With and Without Spinal Cord Transection

Spinal cord injury induces functional and morphological changes in bladder afferent pathways. However, direct evidence for changes in the excitability of afferent nerve activity primarily originating from the bladder has not been clearly demonstrated. Thus, we determined the characteristics of peripheral mechanosensitive bladder afferents in the pelvic nerve and possible afferent changes in Adelta and C fibers after spinal cord injury. Adult female rats were divided into 2 groups, including spinal cord injured and neurologically intact animals. In the spinal cord injury group the spinal cord was transected at Th9 at 4 weeks before functional experiments. For single unit afferent activity monitoring fine filaments were dissected from the L6 dorsal root and bladder afferent fibers were identified. Single unit afferent activity was studied during constant filling with saline. Two afferent patterns were linked to small phasic increases in intravesical pressure during bladder filling, including accelerated and nonaccelerated types. The incidence of the accelerated type was significantly higher in the spinal cord injury group than in the neurologically intact group regarding Adelta and C fibers. However, we found no relationship between conduction velocity and the functional properties of bladder mechanosensitive afferent fibers in neurologically intact or spinal cord injured rats. Results indicate that mechanosensitive bladder afferent activity has several patterns and is facilitated after spinal cord injury, especially in concert with small bladder contractions (micromotions). The functional properties of these individual afferent fibers are not related in an obvious manner to their conduction velocity and, thus, probably the afferent fiber type.

Realistic activity propagation for mean field models of human cortex

Inspired by the great density of neurons in cortex (about 106 per macrocolumn), continuum mean field models (CMFMs) treat the cortex as one continuous neural medium. Interactions between neurons thus become flows of activity spreading in this medium. The most popular propagation model [1] is derived by a two-fold ansatz: a pulse of activity will on one hand spread isotropically with a conduction velocity c, and on the other hand its amplitude will decay exponentially with a distance scale σ. This ansatz reflects action potentials traveling with constant speed through axons and that the number of synapses axons form falls roughly exponentially with distance. However, a pulse in a CMFM means a mass of 105 to 106 neurons pulsing together. It is well known that axons can vary greatly in conduction speed, depending on their myelination and diameter. Hence it is natural to expect that such a mass has a broad conduction velocity distribution f(v), rather than a singular one f(v) = δ(v-c). Furthermore, one still has to expand for large wavelengths in order to derive a manageable partial differential equation (PDE) – a damped wave equation as it turns out. If one calculates the velocity distribution of this approximation, one sees that the Dirac delta peak has softened only towards lower velocities, leaving an unnatural distribution with a hard velocity cut-off. We hence propose a new propagation PDE: where Φ is the activity being propagated, S is a local source (e.g., a firing rate function), Nα the total number of connections, c is the conduction velocity and σ the decay parameter, and n > 0 will usually be chosen as an integer.

Central motor control failure in fibromyalgia: a surface electromyography study

BackgroundFibromyalgia (FM) is characterised by diffuse musculoskeletal pain and stiffness at multiple sites, tender points in characteristic locations, and the frequent presence of symptoms such as fatigue. The aim of this study was to assess whether the myoelectrical manifestations of fatigue in patients affected by FM are central or peripheral in origin.MethodsEight female patients aged 55.6 ± 13.6 years (FM group) and eight healthy female volunteers aged 50.3 ± 9.3 years (MCG) were studied by means of non-invasive surface electromyography (s-EMG) involving a linear array of 16 electrodes placed on the skin overlying the biceps brachii muscle, with muscle fatigue being evoked by means of voluntary and involuntary (electrically elicited) contractions. Maximal voluntary contractions (MVCs), motor unit action potential conduction velocity distributions (mean ± SD and skewness), and the mean power frequency of the spectrum (MNF) were estimated in order to assess whether there were any significant differences between the two groups and contraction types.ResultsThe motor pattern of recruitment during voluntary contractions was altered in the FM patients, who also showed fewer myoelectrical manifestations of fatigue (normalised conduction velocity rate of changes: -0.074 ± 0.052%/s in FM vs -0.196 ± 0.133%/s in MCG; normalised MNF rate of changes: -0.29 ± 0.16%/s in FM vs -0.66 ± 0.34%/s in MCG). Mean conduction velocity distribution and skewnesses values were higher (p < 0.01) in the FM group. There were no between-group differences in the results obtained from the electrically elicited contractions.ConclusionThe apparent paradox of fewer myoelectrical manifestations of fatigue in FM is the electrophysiological expression of muscle remodelling in terms of the prevalence of slow conducting fatigue-resistant type I fibres. As the only between-group differences concerned voluntary contractions, they are probably more related to central motor control failure than muscle membrane alterations, which suggests pathological muscle fibre remodelling related to altered suprasegmental control.

The Effect of Tramadol on the Rat Sciatic Nerve Conduction: A Numerical Analysis and Conduction Velocity Distribution Study

The aim of this study was to document the effect of tramadol as an opioid on individual fibers of rat sciatic nerve. To accomplish this objective, compound action potentials (CAPs) were recorded from isolated nerves treated with tramadol from five different concentration levels. Then recorded CAPs and the control group were analyzed by numerical methods namely Conduction Velocity Distribution (CVD) and Fast Fourier Transform (FFT). The results show that the area under CAP and the time derivative of CAP curves decreases, and the excitability of the nerve trunk falls as well (rheobase and chronaxie increases) with increasing tramadol concentration. CVD deduced by model study was divided into subgroups as SLOW (8-26 m/s), MODERATE (26-44 m/s), MEDIUM (44-60 m/s) and FAST (60-78 m/s). The decrement in percentage relative contribution of these conduction velocity groups starts with a concentration of 0.25 mM tramadol, especially in the subgroup named FAST. The power spectrum shifts from higher frequency region to lower frequency region as the tramadol concentration increases. These findings show that fast conducting fibers are more susceptible to tramadol than medium and moderate groups and tramadol possibly acts on channel activity rather than passive properties (such as space and time constant) of nerve fibers.

Effects of melatonin supplementation on exercise-induced changes in conduction velocity distributions

The mammalian nervous system processes complex information to control complex behaviors. Since the speed of transport of information can be a life-saving phenomenon, it is extremely important to stabilize the rate of these processes. This study aims to investigate the protective effects of melatonin supplementation on acute heavy exercise-induced changes in the nerve conduction velocity distributions (CVD). Remodeling of the sciatic nerve due to heavy exercise demonstrates not only an increase in some parameters (rheobase and chronaxie), but also decreases in maximum depolarization, total area under the compound action potential (CAP), fall-down phase of CAP kinetics and speed of the intermediately conducting group. Acute heavy exercise-induced decreases in the contribution of nerve fibers were mainly found between 1.0 and 1.7 interstimulus interval (ISI) values (46-52 m/s). Presupplementation with melatonin, a powerful antioxidant for nervous tissues, protects the sciatic nerve against all of the aforementioned changes. Presupplementation not only protects the nerve cells from exercise-induced damage, but also increases the contribution of nerve fibers with conduction velocities of 46-52 m/s.