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

A strong linear relationship between Turns/Amplitude peak ratio and ratio at maximal effort

In EMG interference pattern analysis, the peak value of turns to mean amplitude ratio [peak(T/A)] is an established clinically significant marker, but its calculation requires specific software available only in few EMG apparatuses. On the contrary, the turns to mean amplitude ratio obtained at maximal muscle contraction (T/Amax) is easily calculated but less well standardized. We aimed to quantitatively assess the association between T/Amax and peak(T/A). Data were derived from 642 muscle contractions (Nc) from 270 consecutive patients (Np) who underwent EMG at our laboratory (software Dantec Keypoint, QEMG) from May 2015 to September 2016 and had interference patterns obtained from at least one of the following muscles: triceps-lateral head, brachioradialis, extensor digitorum communis and biceps. Statistics were calculated separately for normal and neurogenic muscles. Peak(T/A) was calculated by the built-in "peak ratio" function. T/Amax was calculated by the built-in Interference Pattern analysis function. The ratio with the highest amplitude was selected as T/Amax. Linear regression models provided high Pearson correlation coeffficientscoefficients (R) between peak(T/A) and T/Amax for all 4 muscles, normal or neurogenic, except a subgroup of biceps in patients aged <40y. Specifically, R were: (A) triceps normal 0.79 (Nc = 99), neurogenic 0.83 (Nc = 50) (B) brachioradialis normal 0.81 (Nc = 84), neurogenic 0.78 (Nc = 66) (C) extensor digitorum communis normal 0.72 (Nc = 92), neurogenic 0.73 (Nc = 61) (D) biceps (age > 40y) normal 0.77 (Nc = 77), neurogenic 0.67 (Nc = 62). We conclude that T/Amax has a strong linear association with peak(T/A) and, therefore, the former may be further investigated as a potentially useful quantitative diagnostic marker, especially in cases where the latter is not available.

Tibialis anterior surface EMG parameters change before force output in multiple sclerosis patients

Neuromuscular function has been studied in multiple sclerosis patients with differing levels of disability. Force during maximal voluntary ankle dorsiflexion and surface EMG in tibialis anterior for weakest and strongest legs in 31 patients was compared with 16 control subjects. In the most mildly affected patients strength of dorsiflexion for the strongest leg was not significantly different from that of controls, but integrated mean EMG and median frequency of the power spectrum were significantly lower. In all other patient groups, all parameters measured were different from control values. Results indicate an important change in neuromuscular parameters which precedes loss of the ability to recruit normal force levels. Such changes may imply that the muscles of multiple sclerosis patients are affected even before there is significant evidence of neural motor dysfunction.

Intraoperative recording of the bulbocavernosus reflex

: The bulbocavernosus reflex (BCR) is mediated by the sacral somatic afferent/efferent periphery as well as the sacral cord. Unfortunately, the reflex has suffered from a partly deserved reputation as difficult to implement. However, recent stratagems have improved the test's reliability. Multipulse stimulation (enhanced by double trains as required) and exacting recording technique can yield positive and remarkably reproducible results in patients of all ages and either sex. In this review, we document a 94% baseline BCR acquisition rate among 100 consecutive cases in one institution. Acceptance and routine use of the BCR is needed to help assure optimal post-operative low sacral function in intradural and extradural surgeries at the level of conus medullaris, cauda equina, sacral plexus, and the pudendal nerve. Case studies within this review illustrate the power of the BCR to predict patient outcome or, much more importantly, reverse incipient patient injury in real time.

Levator ani denervation and reinnervation 6 months after childbirth

OBJECTIVE

The objective of the study was to assess the prevalence of levator ani denervation and reinnervation 6 months after the first delivery.

STUDY DESIGN

Ninety-six primigravida women underwent quantitative electromyography of the levator ani during the third trimester and twice postpartum. A 95% confidence interval for normal function was created using interference pattern analysis. Fifty-seven who completed the study are presented in this secondary data analysis. Postpartum muscle sites outside the normal range were considered abnormal. Obstetric and demographic characteristics were assessed.

RESULTS

Of 57 subjects, 70% had no denervation. Of the 30% with denervation at 6 weeks, 35% recovered by 6 months. Obstetric or maternal characteristics were not predictive of denervation or reinnervation, except subjects with persistent denervation tended toward lower body mass index (BMI) independent of mode of delivery.

CONCLUSION

Nearly one-third of women have levator ani denervation after first delivery, but many recover by 6 months. Denervation is not clearly associated with mode of delivery, but higher maternal BMI may be protective.

Effects of changes in intracellular action potential on potentials recorded by single-fiber, macro, and belly-tendon electrodes

Some myopathies are accompanied by abnormal calcium homeostasis. Electromyography (EMG) in such patients shows signs of normal or myopathic EMG when detected by a single-fiber electrode and abnormally increased values in macro EMG. As calcium accumulation might be accompanied by changes in intracellular action potential (IAP) and muscle-fiber propagation velocity, we simulated the effects of such changes on motor unit potentials (MUPs) recorded by different kinds of electrodes. We found that: (1) the requirements for what potential can be accepted as a single-fiber action potential (SFAP) are too rigorous; (2) macro MUP amplitude can increase while SFAP amplitude can decrease when there is an increase in the spatial length of IAP spike; and (3) changes in the second phase of a belly-tendon-detected MUP or M wave could be used for noninvasive detection of increased IAP depolarizing (negative) after-potential.

Changes in intracellular action potential profile affect parameters used in turns/amplitude analysis

The influence of changes in the intracellular action potential (IAP) spatial profile on motor unit potentials (MUPs), number of turns per second (NTs), and mean turn amplitude were simulated and analyzed. We show why measurement of NTs was "the best indicator of neurogenic affection" and why the lower diagnostic yield of turns/amplitude analysis in myopathy could be due to changes in IAP shape caused by elevated free calcium concentration. The results explain the complications observed when interference electromyographic signals obtained during high levels of isometric contractions were analyzed. We show that, in contrast to earlier assumptions, the effect of increased IAP spike duration on NTs was stronger than that of a decrease in muscle fiber propagation velocity (MFPV). The decrease in the NTs could occur without a drop-out of MUs and/or a decrease in their firing rates, and without a change in MFPV and synchronous firing.

Enhancement of the Bulbocavernosus Reflex During Intraoperative Neurophysiological Monitoring through the Use of Double Train Stimulation: A Pilot Study

OBJECTIVE

Electrophysiological bulbocavernosus reflex (BCR) testing, during surgeries in which the constituent neural components are at risk, might supplement other low sacral (S2-4) stimulation/recording techniques. However, intraoperative BCR is not always reliably implemented. We proposed to analyze BCR signals in five surgical patients monitored with the novel application of double train stimulation (DTS) to determine if the potential could be enhanced.

METHODS

We prospectively planned a regime of DTS BCR with a series of intertrain delays in five monitored patients at risk for low sacral neural injury. Patients were maintained with propofol, opiate infusion, and low inhalant anesthesia without muscle relaxant. Cutaneous sensory nerves of the penis (or clitoris) were stimulated using two consecutive pulse trains (DTS). Intertrain delays were 75, 100, 125, 150, 175, 200, and 250 ms. For BCR recording, uncoated paired wires were inserted into the external anal sphincter (EAS) bilaterally. For each trial, waveform amplitude, duration, and turn count measures for the first (single train) and second (double train) response were recorded. Percent increase/decrease of the second train response compared to the first train response was calculated.

RESULTS

There was at least a 30% increase in measures of amplitude, turn count, and duration of the second train response in 22/28, 22/28, and 14/28 of the total trials respectively. There was an insufficient number of independent observations to determine statistical significance.

CONCLUSIONS

Intraoperative BCR is currently obtained with some difficulty using pulse train stimulation. Our preliminary evidence has identified BCR waveform enhancement using DTS and suggests that the reliability of intraoperative BCR acquisition may be further improved by the addition of this technique. Our data are insufficient to define the best intertrain interval.

The role of different EMG methods in evaluating myopathy

For the diagnosis of myopathy, EMG may have an important role along with blood tests, muscle biopsies and genetic testing. This review evaluates different EMG methods in the diagnosis of myopathy. These include manual analysis of individual motor unit potentials and multi-motor unit potential analysis sampled at weak effort. At high effort, turns-amplitude analyses such as the cloud analysis and the peak ratio analysis have a high diagnostic yield. The EMG can seldom be used to differentiate between different types of myopathy. In the channelopathies, myotonia, exercise test and cooling of the muscle are helpful. Macro-EMG, single-fibre EMG and muscle fibre conduction velocity analysis have a limited role in myopathy, but provide information about the changes seen. Analysis of the firing rate of motor units, power spectrum analysis, as well as multichannel surface EMG may have diagnostic potential in the future. EMG is of great importance in the diagnosing of patients with myopathy, preferably a needle electrode and quantitative analyses should be used. A combination of a method at weak effort as well as a method at stronger effort seems optimal.

Physiologically based simulation of clinical EMG signals

An algorithm that generates electromyographic (EMG) signals consistent with those acquired in a clinical setting is described. Signals are generated using a model constructed to closely resemble the physiology and morphology of skeletal muscle, combined with line source models of commonly used needle electrodes positioned in a way consistent with clinical studies. The validity of the simulation routines is demonstrated by comparing values of statistics calculated from simulated signals with those from clinical EMG studies of normal subjects. The simulated EMG signals may be used to explore the relationships between muscle structure and activation and clinically acquired EMG signals. The effects of motor unit (MU) morphology, activation, and neuromuscular junction activity on acquired signals can be analyzed at the fiber, MU and muscle level. Relationships between quantitative features of EMG signals and muscle structure and activation are discussed.

Protocol for clinical neurophysiologic examination of the pelvic floor

Clinical neurophysiologic examination of the pelvic floor is performed worldwide, but there is no consensus on the choice of tests, nor on technical details of individual methods. Standardized methods are, however, necessary to obtain their valid application in different laboratories for the purpose of collection of normative data, comparison of patient data and organization of multi-center studies. It is proposed that in patients with suspected "lower motor neuron" type lesions concentric needle electromyography (CNEMG) is the most informative test to detect pelvic floor denervation/reinnervation, and the external anal sphincter (EAS) muscle is the most appropriate muscle to be examined (either in isolation-when a selective lesion is suspected-or in addition to examination of other muscles). An algorithm consisting of standardized tests including a standardized approach to CNEMG examination of the EAS is presented. The proposed electrophysiologic assessment consists of a computer-assisted analysis of denervation and reinnervation features of the CNEMG signal, a qualitative assessment of reflex and voluntary activation of EAS motor units, and of electrical (or mechanical) elicitation of the bulbocavernosus reflex in those patients in whom manual anogenital stimulation failed to elicit a robust response in the EAS. The proposed protocol could serve as a basis for further studies on validity, sensitivity and specificity of electrophysiologic assessment in patients with different types of "lower motor neuron" involvement of pelvic floor muscles and sacral dysfunction.

EMG-interference pattern analysis

The EMG interference pattern, built up of single motor unit action potentials, may be analyzed subjectively, or objectively by computer aided, quantitative methods, like counting of zero-crossings, counting of spikes, amplitude measurements, integration of the area under the curve, decomposition techniques, power spectrum analysis and turn/amplitude analysis. Since the shape of the interference pattern of healthy muscles is dependent on age, sex, force, muscle, temperature, fatigue, fitness level, recording site and surrounding tissue, electrode type, sensitivity, filters, sampling frequency and threshold level, all methods of analyzing the IP have to be standardized. Quantitative methods of analyzing the EMG interference pattern may be used for monitoring botulinum toxin therapy of dystonia and spasticity, quantifying spontaneous activity, assessment of chronic muscle pain, neuro-urological and proctological function, and diagnosing neuromuscular disorders. For diagnostic purposes, the methods favored are those that use needle electrodes and do not require measurement or monitoring of muscle force. The most well-evaluated methods are those using turn/amplitude analysis, like the cloud methods and the peak-ratio analysis. Peak-ratio analysis has the advantage that reference limits are easy to obtain and that its utility is well established and confirmed by several investigations. Overall, automatic methods of EMG interference pattern analysis are powerful tools for diagnostic and non-diagnostic purposes.

Standardization of anal sphincter electromyography: normative data

OBJECTIVES

Electromyography (EMG) of the external anal sphincter (EAS) is important in the evaluation of conus/cauda lesions, the differential diagnosis of parkinsonism and anal incontinence. The aim of our study was to establish normative data in a sufficiently large group of healthy subjects, using a rigorously standardized examination technique.

METHODS

Sixty-four subjects (aged 19-83 years) without pelvic or neurological disorders were included. Motor unit potentials (MUPs)/interference pattern (IP) samples were obtained from the EAS using multi-MUP and turn/amplitude analyses, respectively. The effect of age, gender, parity, and constipation on MUP/IP parameters was studied. For MUP parameters the lower/upper limits for mean values, and 'outlier' limits, and for IP parameters normal 'clouds' were calculated.

RESULTS

From 112 muscles 15-30 MUPs were sampled. As no effect of evaluated factors on mean values could be demonstrated, common reference values were calculated. Lower/higher limits for mean values were: amplitude 148/661 microV, duration 3.2/7.8 ms, area 87/625 microVms, and number of phases 2. 3/3.7. 'Outlier' limits for individual MUPs were: amplitude 84/1315 microV, duration 1.6/13.8 ms, area 46/1222 microVms, number of phases 2/6. From 95 muscles 2706 IP samples were obtained.

CONCLUSIONS

The presented normative data should allow valid quantitative EMG of the EAS muscle in patients.

Quantitative electromyographic analysis of levator ani and external anal sphincter muscles of nulliparous women

OBJECTIVES

Our aims were to introduce a method of digital quantitative electromyography of the levator ani and external anal sphincter muscles and to establish reference values.

STUDY DESIGN

Fifteen nulliparous, symptom-free women underwent concentric needle electromyographic examination of the levator ani and external anal sphincter. We sampled the levator ani transvaginally at 4 sites and the external anal sphincter at 2 sites. The signal was filtered and amplified, and digital recordings were made at 3 levels of voluntary activation at each site. Analyses of motor unit action potentials and interference patterns were performed with the use of these taped signals. Normal ranges were generated and compared with those established for other striated muscles.

RESULTS

The mean age of the subjects was 28.7+/-7.5 years. A median of 24 motor unit action potentials was recorded in each levator ani, and a median of 6 was recorded in each external anal sphincter. Parameters of the levator ani action potentials were significantly greater than those of the external anal sphincter in amplitude (0.48 vs. 0.37 mV; P =.001), duration (10.40 vs. 8.27 ms; P =.002), number of turns per second (2. 80 vs. 2.28; P<.001), and area (0.65 vs. 0.36; P<.001). Parameters of the interference patterns were significantly greater in the levator ani than in the external anal sphincter in number of turns per second (241.6 vs. 183.9; P =.015), amplitude (302.7 vs. 225.3 microV; P<.0001), activity (95.6 vs 61.2; P =.004), envelope size (861.1 vs 567.6 microV; P<.0001), and number of small segments (105. 8 vs 81.4; P =.047). There were no significant differences between levator ani, external anal sphincter, and published parameters from the biceps muscle with regard to amplitude and duration of motor unit action potentials.

CONCLUSIONS

Electromyography of the levator ani and external anal sphincter is feasible and well tolerated. Our findings confirm that the levator ani muscle has larger, more readily recruited motor units than does the external anal sphincter. Ranges for important quantitative electromyographic parameters for these muscles are similar to those published for the biceps.

Anal sphincter electromyography after vaginal delivery: neuropathic insufficiency or normal wear and tear?

The study was performed to evaluate the potential role of vaginal delivery on innervation of the external anal sphincter (EAS) muscle. Forty-four women, 18 nulliparous and 26 of varying parity (1-4), without genitourinary prolapse, major urogynecological, anorectal, or neurological dysfunction were included. Participants' histories were evaluated by a questionnaire. Quantitative concentric needle electromyography (EMG) using multi-MUP analysis for sampling motor unit potentials (MUPs) in all volunteers, and "turn/amplitude" analysis for interference pattern (IP) analysis in 13 nulliparous and 23 parous women were applied. Pools of MUPs and IPs of parous and nulliparous women were formed and compared using the Mann-Whitney U test. Multiple linear regression analysis was used for evaluation of parity and obstetric variables. No difference between the groups was found in any MUP parameter, while a significant difference was found in two of five IP parameters. On multiple linear regression analysis, the number of deliveries was related to several MUP and IP parameters: the time elapsed since last delivery to MUP, and slight stress urinary incontinence to IP parameters. A group of parous women with (slight) stress incontinence had less "pathologic" MUP parameters, compared to those without. Vaginal delivery is indeed related to EAS muscle EMG abnormalities. However, these are minor and seem not to indicate loss of sphincter function. Our study casts some doubt on the commonly accepted preconception that significant damage to peripheral innervation of the EAS occurs even during uncomplicated deliveries.

On-line quantitative analysis of surface electromyography of the pelvic floor in patients with faecal incontinence

BACKGROUND

Needle electromyography (EMG) remains the 'gold standard' for the assessment of external anal sphincter innervation. It is, however, an invasive and poorly tolerated technique. In this study a quantitative form of surface electromyography was compared with needle EMG of the external anal sphincter.

METHODS

Invasive needle EMG to assess mean fibre density and neuromuscular jitter was compared directly with quantitative surface EMG in 37 patients with faecal incontinence and 12 age-matched controls.

RESULTS

There was a significant positive correlation between mean fibre density on needle EMG and maximum turns rate on surface EMG (rs = 0.48 (95 per cent confidence interval 0.28-0.76), P = 0.003). Furthermore, surface EMG was able to discriminate between patients with normal neuromuscular jitter and those with increased jitter, a measure of progressive denervation and reinnervation, on the basis of reduced rectified mean surface signal (P = 0.02, Fisher's exact test).

CONCLUSION

Quantitative surface EMG may potentially replace invasive needle EMG as the investigation of choice in the assessment of anal sphincter electrophysiology.

Possible mechanisms of muscle cramp from temporal and spatial surface EMG characteristics

In this study, the initiation and development of muscle cramp are investigated. For this, we used a 64-channel surface electromyogram (EMG) to study the triceps surae muscle during both cramp and maximal voluntary contraction (MVC) in four cramp-prone subjects and during cramp only in another four cramp-prone subjects. The results show that cramp presents itself as a contraction of a slowly moving fraction of muscle fibers, indicating that either the spatial arrangement of the motoneurons and muscle fibers is highly related or that cramp spreads at a level close to the muscle. Spectral analyses of the EMG and peak-triggered average potentials show the presence of extremely short potentials during cramp compared with during MVC. These results can also be interpreted in two ways. Either the motoneurons fire with enlarged synchronization during MVC compared with cramp, or smaller units than motor units are active, indicating that cramp is initiated close to or even at the muscle fiber level. Further research is needed to draw final conclusions.

Surface electromyographic evaluation of the asymptomatic human masseter muscle with turns and amplitude analysis

Electromyographic turns, or reversals of direction, per second (TS) and mean amplitude per turn (AT) are variables that have been widely used to assist and support an electrodiagnosis in neuromuscular disorders. The purpose of this study was to explore the feasibility of utilizing the TS and AT in conjunction with surface electrodes as a method for assessing masticatory muscle function. Ten normal subjects were instructed to exert brief isometric contractions at various levels, and the TS and AT were calculated from the surface electromyographic signals of the masseter muscle. Our results showed that the AT increased with contraction at all contraction levels, demonstrating a linear relationship, while the TS showed a nonlinear increase characterized by an initial steep rise followed by a plateau, which was simulated with a third polynomial function. It is considered that the TS and AT may provide valuable physiological information about the underlying mechanisms of recruitment and the firing of motor units.

The utility of interference pattern analysis

The interference pattern of the electrical activity of muscle can be quantified by amplitude measurements, different spike counting methods, and power spectrum analyses. Interference pattern analysis (IPA) methods are used to describe the degree of activation of different muscles, muscle fatigue, occupational work, muscles in chronic pain syndromes, disused muscle, and dystonic muscle treated with botulinum toxin. In patients with neuromuscular disorders, the turns/amplitude analysis is useful for diagnosis. High diagnostic yields can be obtained without force measurements, for example, by using the amplitude as an indicator of force (the peak ratio method) or plotting the amplitude against the turns (cloud analysis). The diagnostic possibilities of the power spectrum analysis and the motor unit firing rate obtained by decomposition techniques are still unclear.

Standardization of anal sphincter electromyography: uniformity of the muscle

The different parts of the external anal sphincter (EAS) are usually regarded as one muscle with common EMG characteristics. This assumption was addressed by comparing the number of continuously firing motor units (MUs) during relaxation, as well as the parameters of motor unit potentials (MUPs) and interference pattern (IP) in the subcutaneous and the deeper parts of EAS. MUPs and IPs were analyzed in 44 subjects (2008 MUPs and 3014 IPs) without uroneurological or proctological disorders, and the number of continuously active MUs in 34 of these subjects was recorded (221 positions). No significant difference was found in IP and most MUP parameters between the two parts of the EAS muscle, but the number of continuously firing MUs was lower in the deeper part. As far as MUP and IP characteristics are concerned, the whole EAS can be considered as one muscle, but some differences in patterns of activation of MUs may exist in different regions.

Surface EMG recorded by branched electrodes during sustained muscle activity

The purpose of the present investigation is to use surface interference EMG recorded by branched electrodes for assessment of muscle fatigue during sustained voluntary isometric contractions at different levels. Level-trigger averaging and turn/amplitude analysis have been applied. The conduction velocity (CV) of excitation was calculated from the time shift of the negative peaks of the averaged potentials (AvPs) derived from the EMG recorded by two electrodes placed along the muscle fibers. The recruitment of new motor units affects the negative amplitude (NA) of AvPs, the number of turns per second and the mean amplitude of turns in a different way depending on the level of sustained contractions. In contrast, the CV declined at all levels of sustained contractions and was the most appropriate parameter for the muscle fatigue assessment. There was a good correlation between CV decrease and torque reduction during sustained maximal efforts. The level-trigger averaging technique of the interference EMG recorded by surface branched electrodes is easy and non-invasive, thus being very convenient for routine application.

Muscle shortening induced by tenotomy does not reduce activity levels in rat soleus

1. A slow postural muscle was tenotomized to determine the role of muscle stretch on chronic recruitment patterns in freely moving animals. 2. Different amounts of muscle shortening were induced in the soleus muscles of ten rats by severing the tendon of insertion (n = 3), the whole Achilles' tendon (n = 4) or the origins and insertions (n = 3). 3. Bipolar wire electrodes were implanted on each muscle to record the electromyographic activity (EMG) under control and tenotomized conditions. The complex interference pattern was continuously analysed to determine the number and amplitude of peak potentials (called turns). The numbers of these 'turns' and their amplitudes were determined during 4 control and at least 5 experimental days. Sham-operated controls and groups matched according to the type of tenotomy were analysed for length changes and pathological changes 5 and 10 days post-tenotomy. 4. The total activity levels in all three tenotomy conditions were not significantly changed when compared with their own control levels. No differences in total activity level were found between the three tenotomized conditions. 5. The normal diurnal patterns of muscle recruitment were preserved during the tenotomized conditions, with the highest levels consistently occurring during the first 3 h of the dark cycle. 6. Tenotomy of the soleus, whether induced by distal (ST), distal and proximal (DT) or Achilles' tenotomy (AT) resulted in muscle shortening (9-26 %). No muscle pathology was found in the ST or AT groups. Degeneration was found in the DT group after 5 days, with further increases at 10 days. 7. These data suggest that the absence of stretch had no discernible influence on the aggregate activity levels in the slow postural soleus muscle. Whether tenotomy caused changes in recruitment within individual step cycles was not evaluated.

Motor unit size estimation of enlarged motor units with surface electromyography

Surface EMG is hardly used to estimate motor unit (MU) characteristics, while its non-invasiveness is less stressful for patients and allows multi-electrode recordings to investigate different sites of the muscle and MU. The present study compares motor unit potentials (MUPs) obtained with surface EMG and macro EMG during voluntary contraction of the biceps brachii muscle of patients with enlarged MUs caused by prior poliomyelitis. Averaged surface MUPs were obtained by means of needle EMG (SMUP1) and surface EMG (SMUP2) triggering. The MUPs area and peak amplitudes correlated well when comparing the macro MUP and SMUP1 of the same MUs. When MU populations of different patients were compared, the SMUP1s and SMUP2s were equally sensitive to pathology as macro MUPs. In this, the late non-propagating positive wave (only present in unipolar recordings) is more robust than the triphasic propagating wave. Therefore, surface EMG can be used for detecting enlarged MUs.

The role of electromyography in neurology

A review is given of the role of electromyography (EMG) for diagnosis, pathophysiological description and monitoring of patients with disorders of the peripheral nervous system. Various EMG methods are presented and their principal differences are discussed. The usefulness of these methods varies depending on the pathology to be studied. With modern quantitative methods for analysis, EMG has become more sensitive and accurate and is therefore an important part in the evaluation of the neurologic patient. EMG results are usually combined with findings from other neurophysiological investigations (neurography, evoked potentials), histochemistry, biochemistry and most importantly with the clinical signs to give as complete a picture of the condition as possible. The usefulness of EMG depends on a number of factors other than the quality of the investigation as such. These aspects are discussed briefly.

Novel measurement for automated interference pattern analysis of the diaphragm

The automated interference pattern analysis for limb muscles was modified to take into account the unique features of the needle EMG of the diaphragm. The modification was successful in recording more accurately the number of small and large segments and the activity levels with inspiratory effort. "Clouds" were generated in ten healthy subjects. The techniques may prove useful in electrophysiological investigations.

Neural network analysis of the EMG interference pattern

This paper investigates the performance of artificial neural networks for analysing and classifying EMG signals from healthy subjects and patients with myopathic and neuropathic disorders. EMG interference patterns (IP) were recorded under maximum voluntary contraction from the right biceps of a total of 50 subjects. Parameters were obtained from the signals using recognized quantification techniques including turns analysis, small segments analysis and frequency analysis. Supervised networks examined were an improved backpropagation network (IBPN), a radial basis network (RBN), and a learning vector quantization network (INQ). Supervised networks using different combinations of parameters from turns analysis and small segments analysis gave diagnostic yields of 60-80%. Combinations using frequency analysis parameters produced similar results. The performance of unsupervised Self-Organising Feature Maps (SOFM) was generally lower than that of the supervised networks. Including personal data (sex and age) did not improve the overall performance.

Sensitivity and specificity of needle electromyography: a prospective study comparing automated interference pattern analysis with single motor unit potential analysis

In this prospective study, automated interference pattern analysis (IPA, "Willison analysis", modified by Stålberg et al. 1983) was compared to the quantitative evaluation of mean motor unit potential duration (QMUP) in 239 muscles from consecutive, unselected patients. The sensitivity and specificity of both methods were calculated with respect to the clinically derived final neurological diagnosis, with histology available for 120 examinations. Whereas specificities were not different for the methods, the sensitivity for detection of abnormal vs. normal was 49% for QMUP and 74% for IPA (P < 0.001). The sensitivity for detection of myopathy or neuropathy was 46% or 38% for QMUP and 75% (P < 0.001) or 53% (P < 0.05) for IPA. Thus, in all instances, IPA had superior sensitivity with unchanged specificity as compared to QMUP. The results of a rapid and purely qualitative visual MUP assessment were statistically not different from QMUP. Although widely used, neither of these methods has been evaluated for its reliability in unselected patients with various grades of disease. Our results indicate that in a routine setting, the best diagnostic strategy might be the automated IPA, which can be quickly obtained in several muscles, followed by muscle biopsy in unclear cases.

Turns-amplitude analysis of the electromyographic recruitment pattern disregarding force measurement. I. Method and reference values in healthy subjects

We used turns-amplitude analysis to characterize the EMG recruitment pattern disregarding force measurement. The electrical muscle pattern of the brachial biceps (BB), abductor pollicis brevis (APB), medial vastus (MV), and anterior tibial (AT) muscles was analyzed during progressive increase in force from rest to maximum using the mean amplitude as an indicator of the force of the muscle. The following parameters were obtained on-line: the maximal ratio of turns to mean amplitude (peak-ratio, PR), the mean amplitude, and the number of time intervals (TI) between turns at PR and at near maximum force (NMF). The highest PR values were obtained in BB, the lowest in MV. Analysis of the distribution of the TI between turns at different degrees of voluntary contraction showed fewer spikes with short duration and small amplitude at high force compared with low force.

Turn and phase counts of individual motor unit potentials: correlation and reliability

Different turn algorithms are used for quantitative motor unit potential (MUP) analysis. To compare their retest reliability, 420 myopathic and neuropathic MUPs were recorded twice and the turn count of the first registration was correlated with that of the second. Reliability was best for the algorithm according to Willison as compared to the conventionally used algorithms based on amplitude criteria for 2 or 3 successive relative extrema. As demonstrated by discriminant analysis, an amplitude limit of 25 microV yielded more useful turn counts than a limit of 50 microV if myopathic MUPs had to be discriminated from normal MUPs. For this discrimination the turn count was superior to the phase count which did not further improve the discriminant model. This was different for the discrimination between normal and neuropathic MUPs. In this case, both parameters measured partly independent features of the MUP and had to be considered together.

AAEM minimonograph #36: basic concepts of electricity and electronics in clinical electromyography

Fundamental principles of electricity provide a basis for understanding the design and operation of electromyography equipment. An intuitive and quantitative explanation of charge, voltage, current, and impedance provides an introduction to the concepts of resistance, capacitance, and input impedance. These concepts form the basis for discussion of filters, amplifiers, electrodes, digital electronics, stimulators, and patient safety. The monograph assumes no specialized training in engineering or mathematics. The topics are discussed at an introductory level to provide understanding for readers with no electronics background and intuitive insight for more experienced readers.

Non-exercising muscle metabolism during exercise

Glycogen decrements have been observed in non-exercising muscles during exercise. We therefore investigated whether the degraded glycogen was retained within the muscle in the form of glycolytic intermediates, or whether it was effluxed from the non-exercising muscles. For these studies a suspension harness was used to unload the hindlimb muscles at rest and during exercise [McDermott et al. (1987) J Appl Physiol 63:1275-1283]. Concentrations of glycogen and glycolytic intermediates glucose 6-phosphate, fructose 6-phosphate, fructose 1,6-bisphosphate, glycerol 3-phosphate, and lactate) were measured in non-exercising and exercising muscles (soleus, plantaris, red and white gastrocnemius) during a 90-min exercise about 15 m/min, 8% grade). On-line electromyographic analysis showed that the contractile activity in the non-exercising muscles was markedly lower than in the exercising muscles. Similar decrements in muscle glycogen levels were observed in both the non-exercising and exercising muscles at the end of the 90-min, exercise bout (P less than 0.05), despite significantly different activity profiles. An increase in tissue lactate concentrations occurred in both non-exercising and exercising muscle (P less than 0.05), although only slight changes in the glycolytic intermediates occurred. The sum total of all the accumulated glycolytic intermediates and lactate (converted to glucosyl units) in the non-exercising muscles only accounted for a small fraction of the glycogen degraded (approximately 15%-28%). We conclude that the metabolism of glycogen is enhanced in non-exercising muscle, and that glycogen utilization is uncoupled from the energetic demands of the muscle. Furthermore, the glycogen mobilized in non-exercising muscle is not retained within the muscle in other metabolite pools.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of turns analysis and motor unit analysis in electromyography

We compared the results of turns analysis and motor unit analysis on 4056 electromyographic interference patterns (IPs) from normal subjects and patients with neuromuscular disorders. The motor unit analysis involved decomposing the IPs into their component motor unit action potentials (MUAPs) using automatic decomposition electromyography (ADEMG). We checked the accuracy of the decompositions by attempting to reconstruct some of the IPs from their identified MUAPs using computer simulations. The simulations revealed that ADEMG typically identified more than 60% (but not all) of the MUAPs in a given IP. Both turns and MUAP properties showed regular and related changes with force, age, muscle, and recording electrode type. The number of turns in each IP was highly correlated with the number of active MUAPs (r = 0.65), the mean MUAP firing rate (r = 0.72), the mean number of turns per MUAP (r = 0.34), and the product of these 3 properties (r = 0.83). The mean amplitude change per turn was highly correlated with the mean MUAP amplitude (r = 0.82), but also depended on the number of turns per MUAP. Due to the lack of a one-to-one relationship between the turns analysis properties and the MUAP properties, the turns analysis properties by themselves did not provide sufficient information to infer unambiguous physiological information about motor unit morphology or firing behavior.

Quantification of gaps in the EMG interference pattern in chronic hemiparesis

This study presents a quantification of the impersistence in the EMG interference pattern (IP) produced during maximal effort by patients with chronic hemiparesis. Monopolar needles were used to record from the flexor carpi radialis (FCR) and extensor carpi radialis longus (ECR) muscles of both the paretic and non-paretic sides of 19 patients with a history of unilateral CVA and 10 healthy control subjects during maximal voluntary isometric wrist flexion or extension. We found more gaps in the IP and fewer total seconds of EMG activity in paretic than in non-paretic or control forearm muscles. The number of gaps was similar in paretic FCR and ECR, but the reduced active time in paretic ECR indicates proportionally more gaps per second of EMG activity. This method provides quantitative measures of both the lapses (gaps in the IP during maximal effort and the inability to sustain EMG activity (total seconds) during long contractions. The latter measure is sufficiently sensitive to distinguish the greater impairment of a paretic wrist extensor than a paretic wrist flexor muscle, and both may prove to be valuable for future comparisons of the severity of paresis and the progress of recovery. These results represent the first quantitative confirmation of previous qualitative descriptions of impersistent recruitment.

Properties of motor unit action potentials recorded with concentric and monopolar needle electrodes: ADEMG analysis

We compared the configurational and firing properties of 7270 motor unit action potentials (MUAPs) recorded with either concentric (CNE) or monopolar (MNE) needle electrodes from the brachial biceps and anterior tibial muscles of 10 healthy young adults (mean age 27 +/- 4.5 years) using automatic decomposition electromyography (ADEMG). In both muscles, mean MUAP amplitude, rise rate, and number of turns were significantly greater when recorded with MNE (paired t-test, P less than 0.001 in each case). Similar findings were observed at all three tested levels of isometric contractile force: threshold, 10% of maximum voluntary contraction (MVC), and 30% MVC. In contrast, there was no significant difference between electrode types on measurements of mean MUAP duration or firing rate (P greater than 0.05 in each case). These findings indicate that it is acceptable to generalize normative data on MUAP duration and firing rate from one electrode type to another, but that measures of MUAP amplitude and complexity require independent normative databases.

AAEE minimonograph #29: automatic quantitative electromyography

The present status of different computerized methods of automatic quantitative electromyography are reviewed. Interference pattern methods-turns analysis, spectral analysis-are efficient, but the results usually cannot be directly related to the physiological properties of the motor units. Integration analysis does not currently have a major role in diagnostic electromyography. Traditional measurement of single motor unit action potentials during weak contraction can be facilitated and made more objective with computer assistance, but only the lowest-threshold motor units in the muscle are amenable to study. A new class of methodologies under development permit the decomposition of interference patterns into their constituent motor unit action potentials for measurement of configurational and behavioral properties. Patient data from these various methods can be statistically compared with normative data bases available on-line in computerized electromyographs. Both quantitative and quantitative electromyography have applications in the neuromuscular electrodiagnostic examination.

Afferent projections to human tibialis anterior motor units active at various levels of muscle contraction

The synaptic efficacy of muscle and cutaneous afferents on single tibialis anterior motoneurones in man was derived from changes in the firing probability of single, voluntarily activated, motor units in response to electrical stimulation of peripheral nerves or skin. The motor units were recorded with a Macro EMG electrode. The Macro motor unit potential (Macro MUP) recorded with this electrode reflects the electrical activity of all of the muscle fibres in a single motor unit. The amplitude of the Macro MUP is positively correlated with the recruitment threshold of the unit. Motor units with different Macro MUP amplitudes were examined at approximately the same level of voluntary contraction (less than 20% of maximum). The synaptic efficacy of muscle and cutaneous afferents was similar for units with small and with large Macro MUP amplitudes. Single motor units were examined at several different levels of muscle contraction. There was no consistent change in the facilitation from muscle afferents but there was less facilitation from cutaneous afferents during stronger contractions. This was not simply a consequence of the units faster firing rate. It is concluded that, with increasing voluntary drive to tibialis anterior motoneurones in man, there is a reduction in transmission in the pathways from cutaneous afferents to tibialis anterior motoneurones. There is no evidence that low and high threshold units (judging from their Macro MUP amplitudes) have different afferent connections.

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.