Normative ranges by curve fitting to raw data.

This study proposes a technique for finding the frequency distributions (FDs) of the median motor distal latencies (MMDL) of healthy and of disease subjects by mathematically analyzing the combined frequency distribution (CFD) of all the subjects that were recorded in an EMG Lab, from the numbers themselves, without any reference to clinical data. The CFD is the algebraic summation of the healthy-group FD and the disease-group FD. Although it is impossible to visually detect these FDs within the CFD numerical values or graphic representation, the hypothesis is that it can be done analytically. Three analytical ways were tested and showed satisfactory results. Also, this study shows the statistics of the overlap between health and disease, i.e. the prediction value of each MMDL, statistics that are of utmost importance, and can not be generated in any other way.

Computing normative ranges without recruiting normal subjects.

Computing normative data by recruiting normal subjects is extremely difficult. However, many who are examined in a typical clinical neurophysiology lab are normal. In this study we show how to use this abundance of referred subjects to compute normative distal latency statistics from the values themselves. If all latencies are displayed on a frequency distribution, the very left side, the shorter latencies, belong to the left side of the Gaussian "bell" of normal subjects. By curve-fitting that side one can compute the coefficients of the latter. We started with an initial range of 2.0-3.6 ms and then recursively added data points until a "goodness-of-fit" criterion maximized. We computed these coefficients from 982 median motor distal latencies, showing highly significant fit (P < 0.00001): mean at 3.76 ms and SD of 0.45 ms. The data analyzed in this study are only an example of the technique. The results are unique in that they were derived mathematically, without using normal subjects.

Turn analysis of the EMG: the amplitude definition of a turn.

Traditionally and arbitrarily an EMG interference signal (EMGIP) "turn" is defined as any 100 microV signal amplitude change. There have not been planned studies challenging this definition. Here, EMGIPs, recorded by coaxial needle electrodes, in MVC, from biceps brachii muscles of 143 subjects, in three diagnostic groups (Normals, Neuropathics, Myopathics), were analyzed in search of the effects of different turn definition amplitude values (TDEF) on the EMGIP number of turns, average turn amplitude, their ratio, and on the cumulative turn amplitude. This study shows significant differences between the diagnostic-groups. It shows that TDEF has significant effect on the number of turns, the average turn amplitude, their ratio, the cumulative amplitude, and that certain TDEFs are significantly better than others in the diagnosis of neuromuscular diseases. Also, it shows that the number of turns and the turns to average amplitude ratio are better measurements than the average turn amplitude and than the cumulative turn amplitude in showing differences between the EMGIPs of the various diagnostic-groups. As such, some of the smaller TDEFs are significantly better diagnostically than the traditional 100 microV value. Also, it shows that better discrimination between the diagnostic-groups may be achieved by applying more than one TDEF value onto the same data. This study leaves the question of the best TDEF or best TDEF sets open for further research in similar and in different paradigms and technical settings.

An EMG index: Its values in health and disease and its changes with fatigue.

This study was designed to measure an EMG index which relates to the width of the motor unit innervation zone under the assumptions made in Lindstrom's model. This index was measured in healthy and in diseased muscles, intramuscularly, in fatigue inducing maximal voluntary contractions. The bicipital EMG interference patterns of 188 subjects in five diagnostic groups (32 healthy, 83 neuropathic, 28 myasthenic, 13 myotonic and 32 myopathic) were recorded with coaxial needle electrodes. From them, our index was computed repeatedly, in periods of 5.84 s each, to complete fatigue. The data display showed that our index decreased with fatigue. This decrement was found to be significant at P=0.00001 when all cases' data was combined. Separately, however, only the normals and the neuropathic groups reached significance at P<0.05. Measured by our index, the five groups divided into two significantly different clusters: (1) The myopathic/myasthenic cluster with large index values, and (2) the normal/neuropathic/myotonic cluster with smaller ones. Several explanations to these findings are entertained. Also, as significant group differences were found, it is safe to anticipate that this index may prove helpful, complementing other EMG indices, in the diagnosis of neuromuscular disorders. The suggested index and its decrement with fatigue deserve additional study.

Muscle fiber conduction velocity and mean power spectrum frequency in neuromuscular disorders and in fatigue.

This study investigated the relation of muscle fiber conduction velocity (MFCV) to difference power spectrum mean frequency (MF), their fatigue trends, and differences between their values and their fatigue trends in various neuromuscular disorders. Electromyographic interference pattern was recorded inside the biceps in continuous isometric maximal voluntary contractions. Each subject was encouraged to pull for as long as possible. Fatigue was calculated as percent of time to complete inability to sustain contraction. The MFCV was computed by cross-correlation. The MF was computed by differencing, windowing, FFT, squaring of coefficient, and repeat averaging. There were 33 healthy, 86 polyneuropathic, 28 myasthenic, 13 myotonic, and 32 myopathic patients. Both MFCV and MF changed significantly with fatigue--the MFCV linearly, while the MF in a markedly nonlinear fashion. Both were found to be insensitive to the end stages of muscle fatigue--the MFCV did not change its slope toward complete fatigue, and the MF did not change at all beyond the 40% fatigue point. A statistically sound fatigue regression equation was derived for each, and a nonlinear equation was found to best describe their relationship. Neither MFCV nor its fatigue changes were found to be significantly different across the neuromuscular disorders. The MF, however, was found to be significantly different in some neuromuscular disorders in both its average values and fatigue trends. This study showed, in contrast to the literature, a nonlinear relationship between MFCV and MF. It also shows that neither the MFCV nor the MF had reasonable diagnostic power on its own; however, the MF was very promising to serve as an adjunct to other variables.

Improved techniques for measuring muscle fiber conduction velocity.

Cross-correlation (CCT) and dip analysis (DAT) are accepted techniques for estimating muscle fiber conduction velocity (MFCV). In the DAT, the product of the power spectrum of the conducted EMG times a cosine function of the MFCV is added to and inseparable from the noise power spectrum. The inclusion of the noise power is the weakness of the DAT. We propose and evaluate 2 new techniques that directly estimate the cosine function and, hence, the MFCV, avoiding the noise power: (1) The power-modulating-component (PMC), which equals the real part of the cross-power-spectrum of the EMG signal divided by its magnitude; and (2) The power spectrum of the PMC (PMCP). We recorded intramuscular from 229 biceps in isometric maximum voluntary contraction. The EMG signals were analyzed by the 4 techniques, and the results were compared in pairwise design (sign-tests and t tests) for quality and bias. The PMC surpassed the DAT (P less than 0.00005); both the CCT and PMCP performed equally well and better than the DAT and the PMC (P less than 0.00005). Also, the new techniques were superior with simulated EMG. In many cases only the PMCP worked. We conclude that the new techniques are valuable in supplementing the others, and most likely will enhance clinical use of MFCV estimations.

Intramuscular EMG coherence in health and in neuromuscular disorders.

The electromyogram (EMG) interference pattern (EMGIP) is the summed activities of many single fiber action potentials (SFAPs) as they propagate past the recording electrodes, and reflects their temporal and spatial relationships and their propagation speed. Comparing EMGIPs from two locations along the same muscle fibers should give insight into changes that were introduced between these two locations. These changes are expected to correlate with normal and abnormal muscle physiology. In this study, the coherence function was used as the comparison tool. This study was designed to measure the coherence between two EMGIPs recorded intramuscularly by two concentric electrodes separated by 1 cm along the same muscle fibers. The intent was to find coherence values in-and differences among-healthy and diseased muscles. There were 191 subjects: 33 healthy, 85 neuropathic, 28 myasthenic, 13 myotonic, and 32 myopathic. The two main features of this coherence analysis were the significant differences in coherence values between some of the groups in the frequency range of 0 to 70 Hz, and the marked lack of coherence between the two recording electrode EMGIPs in the frequency range above 300 Hz in all of the groups. Also, statistical analysis based on coherence values indicated two significantly distinct clusters in the frequency range of 0 to 70 Hz: the myopathy/myasthenic cluster, with relatively high coherence values, and the normal/neuropathy/myotonic cluster, with relatively low coherence values. Coherence-based classification was correct in 67% of subjects. On theoretical grounds, it was expected that increased dispersion of muscle fiber conduction velocities in myopathy will translate into high-frequency coherence differences between the groups, but this was not found. Instead, significant differences were found in the low-frequency range. It is postulated that the latter resulted from changes in the muscle volume conductor differences in packing of the muscle fibers and differences in fibrous tissue that resulted in differences of impedance within the muscles. This study emphasizes the need for further research into the role and possible utilization of the coherence function in electromyography.

Innervation-zone width in disease and its changes with fatigue.

This study was designed to measure the average size of the motor unit functional innervation zone (FINZONE) in healthy and in diseased muscles, intramuscularly, in fatigue-inducing maximal voluntary contractions. The bicipital EMG interference patterns of 188 subjects (32 healthy, 83 neuropathic, 28 myasthenic, 13 myotonic, and 32 myopathic) were recorded with coaxial needle electrodes. From them, the FINZONE size criterion was computed, repeatedly, each 5.84 s to complete fatigue. The data display showed that the FINZONE size diminished with fatigue. Over all groups, this decrement was significant at p = 0.00001. Separately, only the normals and the neuropathic groups reached significance. Measured by the FINZONE size, the five groups divided into two significantly different clusters: (a) the {myopathic/myasthenic} cluster with large FINZONE sizes and (b) the {normal/neuropathic/myotonic} cluster with smaller ones. Several explanations for these findings were entertained. Also, as significant group differences were found, these results may prove helpful, complementing other variables, in the diagnosis of neuromuscular disorders. Both issues (FINZONE diagnostic value and FINZONE size decrement with fatigue) deserve additional study.

Muscle fiber conduction velocity: dip analysis versus cross correlation techniques.

Among the various techniques in use for computing Muscle Fiber Conduction Velocities (MFCV) the Cross Correlation (CCT) and the Dip Analysis (DAT) Techniques are the most similar to each other. The CCT has been applied to intramuscular and surface EMG recordings, while the DAT has been applied to surface recording only. On theoretical grounds the CCT carries higher signal to noise ratio than the DAT and therefore should be preferred over the latter. This study was designated to test and proved the above for intramuscular recording at maximal contractions with real data. In this study 240 subjects had their biceps EMG Interference Pattern recorded intramuscularly at maximal isometric contraction with two concentric needle electrodes separated one cm from one another along and parallel to the muscle fibers. The recording period lasted for 5.84 seconds. One hundred and sixty nine subjects (70%) showed distinct peaks in their cross correlograms, while only in 20 subjects (8%) were dips discernible by DAT. While most peaks in the CCT were high, clear and distinct most dips were shallow and blurred; also, there were only three cases where dips were detected on the DAT but no peaks were detected on the CCT while there were 152 cases where the CCT was superior to the DAT. This study verifies the superiority of the CCT over the DAT in this specific paradigm. Discussed are suggestions on how to improve the DAT by recording and displaying each lead power spectra separately prior to the differential amplifications of the EMG sinal from the two channels.

EMG interference pattern power spectrum analysis in neuro-muscular disorders.

One hundred sixty six subjects, who had clinically proven Neuromuscular (NM) diagnoses and 37 normal controls, had their biceps muscle EMGs, recorded in sustained isometric maximum voluntary contraction (MVC). The EMG signals were repeatedly transformed into power spectra (PS). The PS were then analysed by various statistical methods. The statistical analyses showed an overall significant difference in power between the sexes but only in the Dysschwannian Neuropathy group and no differences due to age; a very highly significant fatigue trend that manifests, to a different extent, in all frequency bands; the groups were significantly different from one another in both total power and in band-specific power, and to differ in their responses to fatigue. These analyses showed that based on PS alone discriminant analysis can separate the cases into only two significantly different groups: normal controls could not be separated from neuropathies, but both were significantly different from Myasthenia Gravis and myopathies. The statistical analysis highlighted as important the use of separate PS frequency bands and the use of a fatigue paradigm for separating the various NM disorders--showing Group-by-Fatigue; Group-by-Band and Group-by-Band-by-Fatigue interactions to be highly significant. All the above mentioned significant features, though, resulted in a low predictive (diagnostic) value by discriminant analysis and even worse by clustering techniques.

Fatigue trends in and the diagnosis of myasthenia gravis by frequency analysis of EMG interference patterns.

Twenty patients with myasthenia gravis were studied. Needle interference patterns at maximal isometric contractions were recorded from the biceps brachii muscles. Each recording lasted for 30 seconds and induced some fatigue. The EMG signals were transformed into power spectra and were analyzed for differences between control and myasthenic fatigue trends and were tested for the power of the frequency variables to classify unknown subjects. Both groups showed a similar averaged spectra for the first 5 seconds. Thereafter, the controls manifested continuous increase in power, and a power peak frequency shift, toward low frequencies. The myasthenics showed an initial increase throughout the frequency ranges; however, later, there was a marked decrease in power and their peak frequency shifted toward the lower frequencies. These fatigue trends differed significantly from one another. Discriminant analysis correctly classified 83% of the subjects. This technique may be helpful in the diagnosis of myasthenia gravis.

A new technique for measuring muscle fiber conduction velocities in full interference patterns.

The motor unit potential shape, mainly its duration and frequency spectra, and the EMG IP crispiness and its frequency spectra are affected by the muscle fiber conduction velocities (MFCVs). Present techniques are somewhat deficient in that they are not adaptable to measure MFCVs continuously and intramuscularly in the presence of interference patterns, and to do so without interfering with the ongoing muscular activity. In this study a cross-correlation with averaging correlograms technique is presented. An EMG needle electrode, with two recording surfaces 1 cm apart, continuously record two channels of EMG activity which is analog-to-digital converted. Contiguous segments of the signals are cross-correlated, the evolved correlograms are averaged together, averaging-out the time-unlocked noise, and averaging-in a peak that represent the average time it takes the EMG signal to propagate from one recording surface to the other. From the distance between these two recording surfaces and the above calculated propagation time the MFCVs can be computed and monitored intramuscularly either in weak or in strong, in isometric or isotonic contractions. But for the fact that a needle is introduced, there is no interference with the muscle electrical activity. It is expected that this technique may add to EMG diagnosis of neuromuscular disorders, will be used to monitor muscular fatigue and applied in normalizing EMG spectra, conditioning them for a better use in diagnostic electromyography.

The effects of amantadine, rimantadine and levodopa on the frequency of fibrillation potentials in denervated muscle.

Right mid-thigh sciatic denervation was performed in 59 rats. Eleven days later they were assigned into 4 groups: a control group that was injected intraperitoneally with normal saline, and 3 test groups that were injected intraperitoneally with amantadine, rimantadine or levodopa (50 mg/kg each), for 3 consecutive days. On the fourteenth day, 2 h after the third injection, electromyography of the soleus-gastrocnemius muscles was performed under pentothal anesthesia. Fibrillation potentials were counted. The statistical analysis showed significant reduction of fibrillations secondary to levodopa and to amantadine injections. Rimantadine did not change the frequency of fibrillations. A stabilizing effect of levodopa and amantadine on the denervated plasmalemma is postulated.

Ethylene oxide-induced polyneuropathy. A clinical and electrophysiologic study.

Occupational exposure to ethylene oxide (ETO) was manifested as a subacute polyneuropathy, with bilateral footdrop and denervation potentials on electromyography as the principal abnormalities in three young adults whom we examined. To our knowledge, this is the second report of neurotoxic effects caused by long-term ETO exposure in humans and brings the number of patients described with symptomatic polyneuropathy to five.

A quantitative study of the electroencephalographic response to levodopa treatment in parkinsonian patients.

A quantitative EEG study was done in order to confirm previous impressions that there is a significant EEG response to levodopa in parkinsonian patients, and in order to trace the existence of dopaminergic mechanisms in the generation of the human EEG. EEGs of twenty-five parkinsonian patients were recorded both before and during levodopa treatment, two to four weeks apart, when levodopa doses reached maintenance levels of 3-5g/d. Derivations from F7-T3, F8-T4, T5-O1, and T6-O2 were recorded and digitally processed into power density spectra. These spectra were analyzed for levodopa effects in a full factorial repeated measures multiple analysis of variance (MANOVA). A significant effect of levodopa treatment on the EEG was found, and localized to the left occipital lobe. This effect manifested as an increase in power in all the EEG frequency bands. These findings are compatible with multiband synchronization of the EEG generating processes, attributable to dopaminergic mechanisms.