Recording characteristics of monopolar EMG electrodes

Motor unit action potentials (MUAPs) and the electromyographic (EMG) interference pattern (IP) were recorded from the biceps muscle of 5 normal subjects using both a concentric needle (CN) and a disposable monopolar needle (MN) electrode. The MUAPs recorded by the MN electrode had higher amplitude and area and were more frequently complex than those recorded with the CN electrode. The MUAP duration and area: amplitude ratio were similar for both electrodes. Although the MN electrode had a larger recording surface, its dimensions (maximum diameter and length of the cone shaped tip) were similar to those of the CN electrode (minor and major axes of the elliptical recording tip). Based on these observations, we infer that the MN electrode may be more selective than the CN electrode, ie, the AP amplitude recorded by the MN electrode decreases faster than the AP amplitude recorded by a CN electrode when the distance of the muscle fiber from the recording electrode increases. Photomicrographs of the MN electrode after use demonstrated no evidence that the insulating material had peeled off. There was also no evidence that MUAP measurement values changed during the recordings as would be expected if the recording surface changed due to peeling of the insulating material.     

The standard concentric needle cannula cannot replace the Macro EMG electrode

ObjectiveTo establish the usefulness of the single use and affordable standard concentric EMG electrode as a substitute for the expensive standard macro electrode.MethodsMacro EMG performed with macro electrode is compared with recordings from the uninsulated cannula of a standard EMG electrode at two different recording depths in the tibialis anterior muscle. This was performed both in muscles with signs of collateral reinnervation and without.ResultsThe amplitude of the motor units recorded with the uninsulated concentric needle cannula were lower for the deeply recorded motor units compared to motor unit potential (MUP) amplitudes recorded with the standard macro electrode. The deeply recorded concentric needle (CN) cannula recorded MUPs amplitudes were also lower than superficially recorded CN cannula MUPs. The standard Macro EMG signals show no difference between deeply and superficially recorded motor units.ConclusionThe uninsulated cannula of the concentric needle electrode cannot replace the standard Macro EMG electrode due to technical reasons, probably from different effects of shunting of the bare cannula in deep vs. superficially recorded motor units.SignificanceThe standard CN electrode could not be used as substitute for the standard Macro EMG needle.     

Jitter recordings with concentric needle electrodes

Neuromuscular jitter is generally recorded with a single fiber (SF) electromyography (EMG) electrode. Due to concern about using reusable needle electrodes, an acceptable alternative for the SF electrode has been sought. This is a review of the issues involved in using disposable concentric needle (CN) electrodes to measure jitter. Signals recorded with CN electrodes frequently represent the summation of many single fiber action potentials, which will decrease the apparent jitter. The influence of these artifacts on the final result also depends on the analysis method. Reference values obtained with CN electrodes correlate with SF EMG values, but they are a few microseconds lower. Overall results show that the CN method is a good alternative to SFEMG and will facilitate the use of jitter analysis. The results must be interpreted with caution, particularly in borderline cases, but they may be acceptable for clinical use when SF electrodes cannot be used. Muscle Nerve 40: 331–339, 2009     

Multifrequency characteristics of disposable and nondisposable EMG needle electrodes

The physical properties of recording electrodes coupled with the input characteristics of recording amplifiers can affect motor unit parameters. In recent years, there has been increased use of disposable needle electrodes; thus, a comparison of impedance characteristics with disposable types is of interest. Impedances at 10, 100, 1000, and 10,000 Hz of eight different electrode models including concentric and monopolar, both disposable and reusable, were measured. For all models of monopolar electrodes, no significant difference in impedance was found between disposable and nondisposable types. Intramodel variability was seen, however, with a twofold difference between minimum and maximum impedances for each model. For concentric electrodes, a moderate difference in impedance was found between disposable and nondisposable types, but less intramodel variability was seen; there was also more intermodel variability. To determine whether the measured impedances could affect recorded motor unit potentials, a theoretical analysis was conducted using typical waveforms along with circuit analysis techniques. Electrode impedances as high as 50 times nominal values caused no significant waveform distortion. © 1993 John Wiley & Sons, Inc.     

EMG of reinnervated motor units: a simulation study

Using computer simulation techniques, reinnervation of motor units (MUs) was studied by increasing the number of muscle fibers in the MU without changing the MU territory. The fiber density (FD) measured by single fiber EMG electrodes, the amplitude, area and number of turns of concentric needle (CN) EMG motor unit action potentials (MUAPs) and the amplitude of macro EMG MUAPs were most affected by partial reinnervation changes. The values of these features increased during simulated advanced reinnervation, as did the number of CNEMG MUAPs that had increased numbers of phases or turns and the mean CNEMG MUAP duration. The increase in macro EMG MUAP amplitude, FD and CNEMG MUAP area were proportional to the increase in the number of muscle fibers in the MU. When loss of muscle fibers due to so-called MU fractionation was simulated, values of all EMG features fell, but were still increased compared to normal. Two patterns of change in SFEMG and macro EMG values were identified that may distinguish between recordings made from reinnervated low force threshold MUs and those from higher force threshold MUs.     

Simulation of concentric needle EMG motor unit action potentials

Computer simulations of motor unit action potentials (MUAPs) as measured by a concentric needle (CN) electromyography (EMG) electrode in normal motor units (MUs) indicated that the MUAP amplitude is determined mainly by the proximity of the electrode to the closest muscle fiber. The area and duration of the simulated MUAPs were affected by all muscle fibers in front of the active recording surface but mainly by those that were less than 2 and 2.5 mm, respectively, from the active recording surface. The MUAP area was also affected by the proximity of the electrode to the closest muscle fiber. The number of phases of the simulated MUAPs increased when the dispersion of the arrival times of individual muscle fiber APs at the electrode was increased. Increased temporal dispersion of APs decreased the MUAP amplitude and area slightly but did not affect the MUAP duration. It is inferred that different features of the CN MUAP are determined by the distribution of muscle fibers within different portions of the MU territory and thus provide complementary information about the MU architecture.     

High‐pass filtering surface EMG in an attempt to better represent the signals detected at the intramuscular level

Surface electromyography (EMG) is often used to represent activation profiles of the underlying musculature. The purpose of this study was to assess the potential of high‐pass (HP) filtering to improve the matching of surface EMG signals to those signals recorded intramuscularly. EMG was recorded at the skin surface over the infraspinatus and supraspinatus muscles as well as from fine‐wire electrodes placed in the infraspinatus, supraspinatus, and teres minor muscles. The surface EMG signals were HP‐filtered at 18 cutoff frequencies (0–510 HZ in 30 HZ increments), and the time‐histories were correlated with the signals from the wire electrodes. HP filtering did not significantly alter the correlated muscle activation waveform relationship between the surface and wire signals until cutoffs reached 240 HZ . HP filtering of the surface signals did not improve the representation of the muscle fiber‐level activation profile, but the results suggest that enough information resides in the high‐frequency components of the signal to reproduce the activation time–history profile of the muscle. Muscle Nerve, 2010     

Single fiber macro versus concentric trigger macro EMG: a comparison of methods.

The values obtained from two different macro EMG methods were compared, and found to be different. Normally, macro electromyography (EMG) is performed with a modified single fiber (SF) needle using the SF potential as a trigger; a new method recommends a modified concentric needle and triggers on the concentric EMG signal. The concentric macro EMG has a 40% to 50% smaller amplitude and area values than data obtained with a SF macro EMG needle. The different values are the result of variant spatial relationships of the respective needles to the motor unit under study, and may be due to a recruitment-dependent bias resulting from different trigger properties of the two methods. The concentric macro EMG needle can be used to estimate motor unit size, to scan the unit, and to investigate its different concentric EMG signals.     

Influence of recording site withing the muscle on motor unit potentials

The influence of the recording site on the motor unit potentials (MUPs) was investigated in the brachial biceps muscle of 8 healthy subjects. The MUPs were recorded with a concentric needle electrode and analyzed with a new decomposition EMG program we call multi-MUP analysis. MUPs had shorter durations and smaller amplitudes at superficial recording sites than at deeper sites in the muscle. This is mainly due to the cannula of the concentric electrode, which records a higher potential at superficial recording sites and partially cancels the recorded potentials from the tip in a differential recording. The MUPs had longer durations and higher amplitudes distally than in the middle of the muscle. The longer durations and spike durations are probably due to increased temporal dispersion at a greater distance from the endplate zone. We do not have an adequate explanation for the larger amplitudes distally in the biceps, they may be due to anatomical factors. To increase the diagnostic sensitivity of quantitative MUP analysis the recordings should be obtained from standardized recording sites. © 1995 John Wiley & Sons, Inc.     

Comparison of standard and pediatric size concentric needle EMG electrodes.

OBJECTIVE: To compare motor unit action potential (MUAP) metrics recorded by standard and pediatric size concentric EMG electrodes. METHODS: Commercial electrodes were used to record MUAPs from biceps brachii, first dorsal interosseous and tibialis anterior muscles in normal subjects and those with amyotrophic lateral sclerosis (ALS). RESULTS: In normal subjects, peak amplitude and area were significantly higher when recorded by the pediatric size electrode in tibialis anterior muscles and peak amplitude recorded in first dorsal interosseous muscles. In ALS subjects, peak amplitude was higher recorded by the pediatric size electrode in tibialis muscle but lower when recorded in first dorsal interosseous muscles. CONCLUSIONS: Differences of MUAP metrics when recording with standard and pediatric size electrodes do not seem to have a clinical relevance. SIGNIFICANCE: Pediatric and standard concentric electrodes record similar MUAP metrics.     

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part I: Turns and amplitude measurements

The electromyographic (EMG) interference pattern (IP) was simulated by adding together motor unit action potentials (MUAPs) of different sizes that had been recorded by a concentric needle EMG electrode. The number of turns (NT) of the simulated IP increased with the number of MUAP discharges. The mean amplitude (MA) difference between successive turns in the IP increased when large amplitude MUAPs were added. Our analysis demonstrates that the MA of the IP is determined mainly by the amplitude of large MUAPs in the signal and that large amplitude spikes are more likely to be generated by single large amplitude MUAPs than by summation of several small amplitude MUAPs.     

Multielectrode surface EMG for noninvasive estimation of motor unit size.

To noninvasively estimate the motor unit size, we present a novel surface electromyographic (EMG) measurement system consisting of a surface multielectrode with four-pin electrodes and a pair of surface-disk electrodes. Surface motor unit action potentials (MUAPs) were recorded with the multielectrode, in the so-called multielectrode surface EMG (MSEMG), which was spatially filtered to localize the sensing area and reduce the noise. In addition, a modified decomposition algorithm, considering the geometrical configuration of the multielectrode, was designed to identify the individual MUAPs in the measured MSEMG. The identified MUAP was subsequently used as the triggering source for the EMG signals recorded by the surface-disk electrodes. From a pool of 34 subjects with neuromuscular diseases and 14 normal subjects, the median amplitudes of surface-disk EMG after spike-triggered averaging, called MSEMG-MUAP, correlated well (r = 0.82, P < 0.0001) with those of macro EMG. Moreover, the MSEMG-MUAP recording during a ramp force contraction exhibited the common size principle phenomenon during motor unit recruitment. The results of this study demonstrate that the MSEMG-MUAP measurement is a feasible approach for estimating the motor unit size from the skin surface.     

Effect of Intraesophageal Electrode Position on Signal Amplitude of the Crural Diaphragm Electromyogram

We studied the effect of electrode position relative to the lower esophageal sphincter (LES) on the crural diaphragm electromyogram (EMG) recording in 15 healthy human subjects. Three coil electrodes, each 1 cm in axial length and spaced 1 cm apart, were positioned on the distal 5 cm of a 6-cm-long Dent sleeve device. Bipolar EMG signals were recorded simultaneously from proximal and distal pairs of electrodes during spontaneous respiration, maximum inspiration with open airway, and maximum inspiration with closed airway. The catheter was positioned so that the side hole at the proximal margin of the sleeve recorded esophageal pressure just above the upper end of the LES. During spontaneous inspiration, the amplitude of the proximal diaphragm EMG signal was significantly higher than the distal. There was a significant difference in the amplitude of the two diaphragm EMG signals during maximum inspiration with open airway, and nearly significant differences in the two EMG signals during maximum inspiration with closed airway. We found that electrode position strongly influences the amplitude of the crural diaphragm EMG signals as measured by intraesophageal electrodes. Assessment of the crural diaphragm EMG with only one pair of electrodes may underestimate the signal amplitude.     

Quantitative EMG in inflammatory myopathy

Fifty-four quantitative electromyographic (EMG) studies were made in 37 patients with inflammatory myopathy (IM) at different points in their clinical course and treatment. All studies were performed in the biceps brachii which varied in clinical strength. Motor unit action potentials (MUAPs) in 45 studies and EMG interference pattern (IP) in 48 studies were recorded using a concentric needle electrode. Macroelectromyographic (Macro-EMG) MUAPs were recorded from 10 patients in 14 studies. MUAP analysis revealed a myopathic pattern (decreased duration and/or area: amplitude ratio) in 69% of studies. IP analysis was more sensitive than MUAP analysis, demonstrating a myopathic pattern in 83% of studies. Macro-EMG MUAP amplitudes were reduced in two studies, minimally increased in one study and normal in the remainder; in 6 (40%) studies, fiber density was slightly increased. Thus, reinnervation does not seem to play an important role in motor unit remodeling in IM.     

Concentric macro electromyography

Concentric EMG electrodes can record from a few (10 to 15) muscle fibers of a motor unit (MU). Macro EMG, is able to record from the majority of muscle fibers in the MU. The macro EMG electrode uses a single fiber action potential (SFAP) on one channel to trigger the time locked cannula (macro) response on the other channel. To study the concentric motor unit action potential (MUAP), alongside the macro potential, we built a needle electrode combining concentric and macro recording surfaces. The study of 240 motor units in 10 healthy subjects with the single fiber (SF macro) and concentric macro (conmac) electrodes revealed no significant differences between macro potentials areas and amplitudes obtained with either electrode. The ability to study a small and a large section of the motor unit simultaneously offers insights into the local or global nature of motor unit changes not otherwise available to the electromyographer. It also reveals which concentric parameters correlate best with the macro potential and, can even be of great help with the newer EMG signal decomposition techniques; by identifying each motor unit by its concentric and macro waveform simultaneously, it will allow for the "marking" of these motor units helping to reduce the risk of their misclassification when the concentric MUAP is used alone.     

Sphenoidal EEG recording using acupuncture needle electrode in complex partial seizure.

Sphenoidal EEG recording using an uninsulated acupuncture needle electrode were performed in 41 patients with or suspected of complex partial seizures of temporal lobe origin. The anterior temporal spikes were detected by the routine EEG in 17 patients (41%) and by the acupuncture sphenoidal needle in 29 patients (70%). The anterior temporal spikes recorded by the acupuncture needle were almost identical in configuration, amplitude and distribution to those recorded by conventional wire or insulated needle sphenoidal electrodes. The sequence in the frequency of spike detection by these 3 types of sphenoidal electrode were SP1-2, T1-2, F7-8 and A1-2 locations. The spikes of maximal amplitude were most frequently recorded by the SP electrode followed by the T1-2 electrode. The placement of the disposable acupuncture needle was simple and safe. Patients experienced minimal discomfort or pain that lasted at most 0.5 h. No complications occurred. The records were generally free of artifacts. It is concluded that the acupuncture needle can be used as sphenoidal electrode in outpatient EEG recording for the diagnosis of complex partial seizures of anterior temporal-origin.     

Quantitative EMG and motor unit recruitment threshold using a concentric needle with quadrifilar electrode

According to Henneman's size principle, small motor units are recruited before large ones. We used the electromyographic (EMG) signal decomposition technique to determine the quantitative relationships between five motor unit action potential (MUAP) parameters (amplitude, duration, area, thickness, and size index) and the recruitment threshold of the motor units recruited up to 50% of the maximum voluntary contraction in the first dorsal interosseous, biceps brachii, rectus femoris, and tibialis anterior muscles of 5 healthy young men. In each muscle, the amplitude, duration, area, and size index had significant, positive high correlations with the motor unit recruitment thresholds. We conclude that the size principle applies to recordings made with concentric needle EMG electrodes under special recording conditions, and therefore that more importance should be attached to the patient's contraction force during EMG examinations in order to evaluate MUAPs for electrodiagnostic purposes.     

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part II: Activity, upper centile amplitude, and number of small segments

We have defined three new features of the electromyographic (EMG) interference pattern (IP): activity, upper centile amplitude (UCA), and number of small segments (NSS). These parameters were measured in simulated IPs constructed by adding together motor unit action potentials (MUAPs) recorded with a concentric needle EMG electrode. The activity increases linearly with the number of MUAP discharges to approximately 80% of its theoretical maximum value. The UCA correlates strongly with the peak-to-peak amplitude of the largest MUAP in the IP and the mean segment amplitude and does not depend on the discharge rate of the largest MUAPs. We infer that the UCA defines the upper limit of the peak-to-peak amplitude of the MUAPs contained in the IP. The NSS increases with the number of MUAP discharges, but reaches a constant value at higher MUAP discharge rates, probably because small amplitude MUAPs are masked by the large amplitude MUAPs. The potential value of these parameters in automated IP analysis is discussed.     

Diaphragm motor responses to phrenic nerve stimulation in ALS: Surface and needle recordings

Objective

In studies of phrenic nerve (PN) conduction in amyotrophic lateral sclerosis (ALS) both motor response amplitude and latency have been reported as abnormal. However, correlation with diaphragm motor unit loss, and with diaphragmatic function has not been fully evaluated.

Pitfalls and errors in measuring jitter

The safety factor of neuromuscular transmission can be assessed by measuring the neuromuscular jitter, which reflects the time variability of processes in the motor end-plate. Jitter is increased in any condition with disturbed end-plate function, such as myasthenic conditions and ongoing reinnervation. Jitter is increasingly being measured with concentric needle (CN) electrodes, which are more prone to artefacts than single fiber EMG recordings.The objective of this review is to identify and demonstrate pitfalls that can be seen with CN jitter measurements, made with both voluntary activation and electrical stimulation.With voluntary activation, errors are caused by poor signal quality; inappropriate time reference points on the signal; an irregular firing rate; and signals with dual latencies, i.e., “flip-flop.” With electrical stimulation, additional errors result from insufficient stimulation intensity; from abrupt change in firing rate; and from axon reflexes.Many pitfalls cannot be avoided during recording and can only be detected during post-processing.It is critical to be aware of these artefacts when measuring jitter with CN electrodes.