Analysis of the electromyographic interference pattern

Understanding EMG PDF Changes With Motor Unit Potential Amplitudes, Firing Rates, and Noise Level Through EMG Filling Curve Analysis

EMG filling curve characterizes the EMG filling process and EMG probability density function (PDF) shape change for the entire force range of a muscle. We aim to understand the relation between the physiological and recording variables, and the resulting EMG filling curves. We thereby present an analytical and simulation study to explain how the filling curve patterns relate to specific changes in the motor unit potential (MUP) waveforms and motor unit (MU) firing rates, the two main factors affecting the EMG PDF, but also to recording conditions in terms of noise level. We compare the analytical results with simulated cases verifying a perfect agreement with the analytical model. Finally, we present a set of real EMG filling curves with distinct patterns to explain the information about MUP amplitudes, MU firing rates, and noise level that these patterns provide in the light of the analytical study. Our findings reflect that the filling factor increases when firing rate increases or when newly recruited motor unit have potentials of smaller or equal amplitude than the former ones. On the other hand, the filling factor decreases when newly recruited potentials are larger in amplitude than the previous potentials. Filling curves are shown to be consistent under changes of the MUP waveform, and stretched under MUP amplitude scaling. Our findings also show how additive noise affects the filling curve and can even impede to obtain reliable information from the EMG PDF statistics.

Tutorial. Surface electromyogram (sEMG) amplitude estimation: Best practices

This tutorial intends to provide insight, instructions and "best practices" for those who are novices-including clinicians, engineers and non-engineers-in extracting electromyogram (EMG) amplitude from the bipolar surface EMG (sEMG) signal of voluntary contractions. A brief discussion of sEMG amplitude extraction from high density sEMG (HDsEMG) arrays and feature extraction from electrically elicited contractions is also provided. This tutorial attempts to present its main concepts in a straightforward manner that is accessible to novices in the field not possessing a wide range of technical background (if any) in this area. Surface EMG amplitude, also referred to as the sEMG envelope [often implemented as root mean square (RMS) sEMG or average rectified value (ARV) sEMG], quantifies the voltage variation of the sEMG signal and is grossly related to the overall neural excitation of the muscle and to peripheral parameters. The tutorial briefly reviews the physiological origin of the voluntary sEMG signal and sEMG recording, including electrode configurations, sEMG signal transduction, electronic conditioning and conversion by an analog-to-digital converter. These topics have been covered in greater detail in prior tutorials in this series. In depth descriptions of state-of-the-art methods for computing sEMG amplitude are then provided, including guidance on signal pre-conditioning, absolute value vs. square-law detection, selection of appropriate sEMG amplitude smoothing filters and attenuation of measurement noise. The tutorial provides a detailed list of best practices for sEMG amplitude estimation.

A scoping review of current and emerging techniques for evaluation of peripheral nerve health, degeneration, and regeneration: part 1, neurophysiology

Peripheral neuroregeneration research and therapeutic options are expanding exponentially. With this expansion comes an increasing need to reliably evaluate and quantify nerve health. Valid and responsive measures that can serve as biomarkers of the nerve status are essential for both clinical and research purposes for diagnosis, longitudinal follow-up, and monitoring the impact of any intervention. Furthermore, such biomarkers can elucidate regeneration mechanisms and open new avenues for research. Without these measures, clinical decision-making falls short, and research becomes more costly, time-consuming, and sometimes infeasible. As a companion to Part 2, which is focused on non-invasive imaging, Part 1 of this two-part scoping review systematically identifies and critically examines many current and emerging neurophysiological techniques that have the potential to evaluate peripheral nerve health, particularly from the perspective of regenerative therapies and research.

Median nerve ultrasound cross sectional area and wrist-to-forearm ratio in relation to carpal tunnel syndrome related axonal damage and patient age

Objective

Primary objective was to retrospectively examine the effects of patient age and carpal tunnel syndrome (CTS) related axon loss on median nerve (MN) high resolution ultrasound (HRUS) in younger and older patients. HRUS parameters evaluated in this study were MN cross sectional area at the wrist (CSA) and wrist-to-forearm ratio (WFR).

Methods

The material comprised 467 wrists of 329 patients. The patients were categorized into younger (<65 years) and older (≥65 years) groups. Patients with moderate to extreme CTS were included in the study. Axon loss of the MN was assessed by needle EMG and graded by the interference pattern (IP) density. The association between axon loss and CSA and WFR was studied.

Results

The older patients had smaller mean CSA and WFR values compared to the younger patients. CSA correlated positively to the CTS severity only in the younger group. However, WFR correlated positively to CTS severity in both groups. In both age groups, CSA and WFR correlated positively with IP reduction.

Conclusions

Our study complemented recent findings on the effects of patient age on the CSA of the MN. However, although the MN CSA did not correlate with the CTS severity in older patients, the CSA increased in respect to the amount of axon loss. Also, as a new result, we presented the positive association of WFR with CTS severity among older patients.

Significance

Our study supports the recently speculated need for different MN CSA and WFR cut-off values for younger and older patients in assessing the severity of CTS. With older patients, WFR may be a more reliable parameter to assess the CTS severity than the CSA. CTS related axonal damage of the MN is associated to additional nerve enlargement at the carpal tunnel intel site.

Detecting motor unit abnormalities in amyotrophic lateral sclerosis using high-density surface EMG

OBJECTIVE

The purpose of this study was to detect specific motor unit (MU) abnormalities in people with amyotrophic lateral sclerosis (ALS) compared to controls using high-density surface electromyography (HD-SEMG).

METHODS

Sixteen people with ALS and 16 control subjects. The participants performed ramp up and sustained contractions at 30% of their maximal voluntary contraction. HD-SEMG signals were recorded in the vastus lateralis muscle and decomposed into individual MU firing behavior using a convolution blind source separation method.

RESULTS

In total, 339 MUs were detected (people with ALS; n = 93, control subjects; n = 246). People with ALS showed significantly higher mean firing rate, recruitment threshold, coefficient of variation of the MU firing rate, MU firing rate at recruitment, and motoneurons excitability than those of control subjects (p < 0.001). The number of MU, MU firing rate, recruitment threshold, and MU firing rate at recruitment were significantly correlated with disease severity (p < 0.001). Multivariable analysis revealed that an increased MU firing rate at recruitment was independently associated with ALS.

CONCLUSIONS

These results suggest increased excitability at recruitment, which is consistent with neurodegeneration results in a compensatory increase in MU activity.

SIGNIFICANCE

Abnormal MU firing behavior provides an important physiological index for understanding the pathophysiology of ALS.

Calculating Turns/Amplitude peak ratio of EMG interference pattern by using logistic curve fitting

The aim of the study was to test whether logistic curve fitting (LCF) of Turns = f(Amplitude) plots of single muscle contractions can provide a reliable alternative method for peak-ratio calculation. EMG signals from 74 biceps and 62 triceps contractions were analyzed by applying LCF to Turns = f(Amplitude) plots. Peak-ratio (peak-ratio2) could then be calculated as the point of the fitted line with the highest Turn/Amplitude value. LCF yielded R² values > 0.95 in the vast majority of contractions studied (68/74 biceps and 53/62 triceps). Peak-ratio2 values had a very strong linear relationship with the corresponding values calculated by the traditional method (peak-ratio1) in both normal and neurogenic conditions. Furthermore, ROC curve analysis showed that peak-ratio1 and peak-ratio2 had similar AUC values. Based on the LCF equation, peak-ratio = T2*(p - 1)/A0*p*(p - 1)^1/p. Therefore, peak-ratio is proportional to the maximum number of turns (T2), positively correlated to the rate of turns' increment at the midpoint of the curve (p) and negatively correlated to the mean amplitude at the midpoint of the curve (A0). A0 is the variable that best discriminates between normal and neurogenic conditions. We provide an alternative method for peak-ratio calculation and show the variables that influence this sensitive marker of neurogenic disease.

Clinical and neurophysiological characterization of muscular weakness in severe COVID-19

Objective

To report clinical and electroneuromyographic (ENMG) characteristics of patients affected by severe COVID-19 infection, evaluated for muscular weakness.

Materials and methods

ENMGs performed for evaluation of diffuse weakness in patients who could not be discharged from semi-intensive care COVID unit because of difficulties in ventilation weaning were reviewed. Patients with severe COVID-19 infection who had undergone endotracheal intubation and able to co-operate were considered. ENMG protocol was focused on neurophysiological items that excluded or confirmed critical illness polyneuropathy (CIP), myopathy (CIM), or polyneuromyopathy (CIPM). Standardized clinical evaluation was performed using Medical Research Council (MRC) sum score.

Results

Eight patients were included in the study. All presented known risk factors for intensive care unit-acquired weakness (ICU-AW), and none of them had history of underlying neuromuscular disorders. ENMG findings were normal in two patients, while only two patients had an altered MRC sum score (< 48). Neuromuscular involvement was diagnosed in 6/8 patients (75%): 2 had CIP, 1 had possible CIM, 1 had CIPM, while 1 patient, with clinically evident weakness but equivocal ENMG findings, was classified as ICU-AW. Finally, 1 patient was diagnosed with acute demyelinating neuropathy. Patients with neuromuscular involvement were those with longer intubation duration and higher levels of IL-6 at admission.

Conclusion

Neuromuscular complications are frequent in severe COVID-19 and cannot be excluded by MRC sum scores above 48. Standardized ENMG is helpful in guiding diagnosis when clinical evaluation is not reliable or possible. Elevated IL-6 at admission may be a predictor biomarker of ICU-AW in COVID-19.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10072-021-05110-8.

Increased resistance towards fatigability in patients with facioscapulohumeral muscular dystrophy

PURPOSE

In facioscapulohumeral muscular dystrophy (FSHD) fatigue is a major complaint. We aimed to investigate whether during isometric sustained elbow flexions, performance fatigability indexes differ in patients with FSHD with respect to healthy controls.

METHODS

Seventeen patients with FSHD and seventeen healthy controls performed two isometric flexions of the dominant biceps brachii at 20% of their maximal voluntary contraction (MVC) for 2 min and then at 60% MVC until exhaustion. Muscle weakness was characterized as a percentage of predicted values. Maximal voluntary strength, endurance time and performance fatigability indices (mean frequency of the power spectrum (MNF), muscle fiber conduction velocity (CV) and fractal dimension (FD)), extracted from the surface electromyogram signal (sEMG) were compared between the two groups.

RESULTS

In patients with FSHD, maximal voluntary strength was 68.7% of predicted value (p < 0.01). Compared to healthy controls, FSHD patients showed reduced MVC (p < 0.001; r = 0.62) and lower levels of performance fatigability, characterized by reduced rate of changes in MNF (p < 0.01; r = 0.56), CV (p < 0.05; 0.37) and FD (p < 0.001; r = 0.51) and increased endurance time (p < 0.001; r = 0.63), during the isometric contraction at 60% MVC.

CONCLUSION

A decreased reduction in the slopes of all the considered sEMG parameters during sustained isometric elbow flexions suggests that patients with FSHD experience lower levels of performance fatigability compared to healthy controls.

Developing normal number of small segments-activity clouds of the electromyography interference pattern

BACKGROUND

Number of small segments (NSS) and activity analysis is a mature method for electromyographic automatic interference pattern analysis (IPA), but there are few reports on the application of this technique. Our objective was to establish normal reference values of NSS-activity clouds.

METHODS

The NSS and activity data of the sternocleidomastoid, deltoid, biceps brachii (long head), extensor digitorum communis, abductor digiti minimi, vastus medialis, tibialis anterior, and gastrocnemius (lateral head) muscles were obtained from 34 men and 25 women, aged 15-80 years, using concentric needle electrodes. A linear regression of log(NSS) vs log(activity) was performed and the slope, intercept and standard deviation were calculated for each muscle. These variables were transformed back to the original parameters to yield clouds.

RESULTS

Normal NSS-activity clouds for the above eight muscles were obtained.

CONCLUSIONS

Normal reference values of NSS-activity may facilitate detection of early and mild neurogenic and myogenic abnormalities.

Quantitative Evaluation of Interference Patterns on Electromyography in Neuropathy

OBJECTIVE

The aim of this study was to develop a quantitative evaluation method of interference patterns on needle electromyography that is easy to apply in clinical use and to examine its usefulness. Diagnostic electrophysiological assessments are important for physiatrists, and correct diagnosis and assessment are essential for proper rehabilitation.

DESIGN

A total of 112 maximum interference patterns of upper extremity muscles suspected of being affected by neuropathy were quantitatively evaluated based on the parameters of integration values, mean amplitudes, the number of peaks, and activity. "Activity" was defined as the sum of the time during which myoelectric signals were recorded during 1 sec with maximum voluntary contraction, and it was expressed as a percentage. The relationships of the previous parameters with spontaneous pathological potentials and polyphasic motor unit potentials were examined.

RESULTS

The area under the curve of the receiver operating characteristic curve for the diagnosis of neuropathy was the highest using activity (0.917). The integral value and mean amplitude were useful for the diagnosis of cases with chronic neuropathy showing slightly decreased interference patterns.

CONCLUSIONS

The quantitative evaluation of the maximal contraction interference pattern in this study was useful for the diagnosis of neuropathy.

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.

The use of electromyography interference pattern analysis to determine muscle force of the deep digital flexor muscle in healthy and laminitic horses

BACKGROUND

In equine laminitis, the deep digital flexor muscle (DDFM) appears to have increased muscle force, but evidence-based confirmation is lacking.

OBJECTIVES

The purpose of this study was to test if the DDFM of laminitic equines has an increased muscle force detectable by needle electromyography interference pattern analysis (IPA).

ANIMALS AND METHODS

The control group included six Royal Dutch Sport horses, three Shetland ponies and one Welsh pony [10 healthy, sound adults weighing 411 ± 217 kg (mean ± SD) and aged 10 ± 5 years]. The laminitic group included three Royal Dutch Sport horses, one Friesian, one Haflinger, one Icelandic horse, one Welsh pony, one miniature Appaloosa and six Shetland ponies (14 adults, weight 310 ± 178 kg, aged 13 ± 6 years) with acute/chronic laminitis. The electromyography IPA measurements included firing rate, turns/second (T), amplitude/turn (M) and M/T ratio. Statistical analysis used a general linear model with outcomes transformed to geometric means.

RESULTS

The firing rate of the total laminitic group was higher than the total control group. This difference was smaller for the ponies compared to the horses; in the horses, the geometric mean difference of the laminitic group was 1.73 [geometric 95% confidence interval (CI) 1.29-2.32], and in the ponies this value was 1.09 (geometric 95% CI 0.82-1.45).

CONCLUSION AND CLINICAL RELEVANCE

In human medicine, an increased firing rate is characteristic of increased muscle force. Thus, the increased firing rate of the DDFM in the context of laminitis suggests an elevated muscle force. However, this seems to be only a partial effect as in this study, the unchanged turns/second and amplitude/turn failed to prove the recruitment of larger motor units with larger amplitude motor unit potentials in laminitic equids.

Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015

REASONS FOR PERFORMING STUDY

In cases of laminitis, an increased muscle force or contracture of the deep digital flexor muscle (DDFM) is suggested, but evidence-based research is lacking.

OBJECTIVES

To test if the DDFM of laminitic equines shows an increased muscle force detectable by needle-EMG including Interference Pattern Analysis (IPA).

STUDY DESIGN

Cross-sectional study.

METHODS

Three groups consisted of Group 0 (control): 6 Royal Dutch Sport horses, 3 Shetland ponies and one Welsh pony (healthy, sound adults, mean ± s.d. weight 411 ± 217 kg). Group 1: 3 Royal Dutch Sport horses, one Friesian, one Haflinger, one Icelandic horse, 2 Welsh ponies, one miniature Appaloosa and 6 Shetland ponies (adults, mean ± s.d. weight 310 ± 172 kg) suffering from acute or chronic laminitis. EMG measurements including firing frequency (F) and IPA parameters Turns/Second (T), Amplitude/Turn (M) and Ratio M/T (R) were performed. ANOVA was used to analyse data. P values of P<0.05 were considered significant.

RESULTS

Mean ± s.d. F of Group 0 and Group 1 was 53 ± 11 and 72 ± 21 Hz, mean ± s.d. T was 112 ± 57 and 106 ± 42, mean ± s.d. M was 284 ± 51 and 254 ± 38 μV and mean ± s.d. R was 0.39 ± 0.17 and 0.42 ± 0.16%, respectively. The firing frequency of Group 1 was significantly higher compared to Group 0 (P = 0.02), whereas other differences were not significant.

CONCLUSIONS

In human medicine, an increased firing frequency is a characteristic of increased muscle force [1,2]. Thus, the increased firing frequency of the DDFM in case of laminitis suggests an elevated muscle force. As all parameters show a high variance, a repeated study including a larger test group is advised. Ethical animal research: Data collection from controls was approved by the Animal Welfare Committee of Utrecht University, approval number 2008.III.07.061 and 2013.III.01.012. Clinical cases were privately owned and written owner consent was obtained.

SOURCE OF FUNDING

None. Competing interests: None declared.

Multi-Motor Unit Potential Analysis and Other Quantitative Techniques for Laryngeal Electromyogram

Reference values for motor unit potentials of laryngeal muscles, the thyroarytenoid (TA) and cricothyroid (CT) muscles, have been collected using multi-motor unit potential quantitative electromyogram analysis technique with concentric quantitative electromyogram-needle electrode type in 40 healthy volunteers. The method is well tolerated, easy to perform, and examination of one muscle takes usually around 5 minutes. The mean motor unit potential amplitude of both muscles was significantly larger in men than in women. The method can safely be used in clinical routine. Other quantitative electromyogram methods are also shortly reviewed.

Estimating the tendency of motor unit recruitment during steady-hold and rapid contractions using surface EMG and Turns-amplitude analysis

PURPOSE

The purpose of this study was to investigate changes in the interference pattern in surface electromyography (EMG), and its relationship with the tendency of motor unit (MU) recruitment during steady-hold and rapid muscle contractions.

METHODS

Fifteen healthy adults (eight females and seven males, 22.6 ± 1.5 years old) performed steady-hold and rapid isometric contractions of the bicep brachii, adductor pollicis, and tibialis anterior muscles at various force levels. Surface EMG recordings were analyzed using Turns-Amplitude Analysis (TAA).

RESULTS

During steady-hold contractions, the number of turns per second (T/s) increased exponentially with force during submaximal contractions, and plateaued after force levels of 66, 70 and 57 % MVC for the tibialis anterior, bicep brachii and adductor pollicis muscles, respectively. These force levels were proximate to the maximal recruitment threshold (MaxRT) reported previously. The slopes of the T/s-force relationships before the MaxRT were significantly greater than the slopes after the MaxRT for all three muscles tested. During rapid contraction, the slopes of the T/s-force relationships were significantly lower than the slopes of the steady-hold contraction at 20-40 % MVC in all three muscles, and for 40-60 % MVC in TA muscles.

CONCLUSIONS

Our results suggested that the changes in the number of turns in surface EMG with respect to muscle force can be used to estimate the force levels at which the majority of the MUs to be recruited, and completion of MU recruitment was observed at lower force levels during rapid muscle contraction.

Interventions for fatigue in peripheral neuropathy

BACKGROUND

Persistent feelings of fatigue (or subjective fatigue), which may be experienced in the absence of physiological factors, affect many people with peripheral neuropathy. A variety of interventions for subjective fatigue are available, but little is known about their efficacy or the likelihood of any adverse effects for people with peripheral neuropathy.

OBJECTIVES

To assess the effects of drugs and physical, psychological or behavioural interventions for fatigue in adults or children with peripheral neuropathy.

SEARCH METHODS

On 5 November 2013, we searched the Cochrane Neuromuscular Disease Group Specialized Register, CENTRAL, MEDLINE, EMBASE, CINAHL Plus, LILACS and AMED. We also searched reference lists of all studies identified for inclusion and relevant reviews, and contacted the authors of included studies and known experts in the field to identify additional published or unpublished data. We also searched trials registries for ongoing studies.

SELECTION CRITERIA

We considered for inclusion randomised controlled trials (RCTs) and quasi-RCTs comparing any form of intervention for fatigue management in adults with peripheral neuropathy with placebo, no intervention or an alternative form of intervention for fatigue. Interventions considered included drugs, pacing and grading of physical activity, general or specific exercise, compensatory strategies such as orthotics, relaxation, counselling, cognitive and educational strategies.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed risk of bias and extracted study data. We contacted study authors for additional information. We collected information on adverse events from the included trials.

MAIN RESULTS

The review includes three trials, which were all at low risk of bias, involving 530 people with peripheral neuropathy. The effects of amantadine from one randomised, double-blind, placebo-controlled, cross-over trial comparing amantadine with placebo for the treatment of fatigue in 80 people with Guillain-Barré syndrome (GBS) were uncertain for the proportion of people achieving a favourable outcome six weeks post-intervention (odds ratio (OR) 0.56 (95% confidence interval (CI) 0.22 to 1.35, N = 74, P = 0.16). We assessed the quality of this evidence as low. Two parallel-group randomised double-blind, placebo-controlled trials comparing the effects of two doses of ascorbic acid with placebo for reducing fatigue in adults with Charcot-Marie-Tooth disease type 1A (CMT1A) showed that the effects of ascorbic acid at either dose are probably small (standardised mean difference (SMD) -0.12 (95% CI -0.32 to 0.08, n = 404, P = 0.25)) for change in fatigue after 12 to 24 months (moderate quality evidence). Neither ascorbic acid study measured fatigue at four to 12 weeks, which was our primary outcome measure. No serious adverse events were reported with amantadine. Serious adverse events were reported in the trials of ascorbic acid. However,risk of serious adverse events was similar with ascorbic acid and placebo.

AUTHORS' CONCLUSIONS

One small imprecise study in people with GBS showed uncertain effects of amantadine on fatigue. In two studies in people with CMT1A there is moderate-quality evidence that ascorbic acid has little meaningful benefit on fatigue. Information about adverse effects was limited, although both treatments appear to be well tolerated and safe in these conditions.There was no evidence available from RCTs to evaluate the effect of other drugs or other interventions for fatigue in either GBS, CMT1A or other causes of peripheral neuropathy. The cost effectiveness of different interventions should also be considered in future randomised clinical trials.

[Electromyography (EMG) and neurography in patients with severe neuromuscular diseases]

BACKGROUND

Many neuromuscular diseases are potentially severe, and EMG and neurography are methods used in the assessment of these conditions.

METHOD

The article is based on the authors' knowledge and experience, with special emphasis on the use of these methods in the assessment of severe diseases affecting striated muscle and peripheral nerves. A PubMed search was performed with the cut-off fifteen years back in time, and in addition a discretionary selection was made of articles known to the authors.

RESULTS

EMG is the most valuable method for assessing myopathy, and neurography provides most information about neuropathy, but the methods are complementary. These examinations are the most sensitive for diagnosing some conditions (for example myasthaenia) A high level of expertise is necessary for diagnosing these conditions.

INTERPRETATION

EMG and neurography are important and often necessary means of assessing patients with severe neuromuscular disease.

On the relationship between features extracted from EMG and force for constant and dynamic protocols

The main objective of this study was to characterize the relationship between electromyography and force based on the results obtained from a developed analysis tool. The developed tool presents interesting features for the study of this relationship. Among them, it can be highlighted the possibility of simultaneous analysis of various features in the time domain (obtained from electromyographic signals), and the generation of graphics that allow the visualization of the relation between the selected features and the force signal. The tool also allows a feature evaluation based on different models (e.g., linear, quadratic and exponential) allowing a better understanding of the EMG-force relationship. In order to evaluate the developed tool and study the EMG-force correlation, electromyographic signals (EMG) and force measurements were collected from 15 subjects while executing eight different experimental protocols. The obtained results showed that statistical features (e.g., kurtosis and skewness) are less sensitive to dynamic force protocols; and also that features related to the amplitude of the signal are more appropriate to represent the relationship between EMG and force during the execution of constant force protocols. These results, besides having several practical applications, can be used as part of EMG signals simulators, developed for different applications, such as the evaluation of automatic systems used in the decomposition of EMG signals.

Concentric Needle Quantitative EMG of Pubovisceralis Muscle Group: Normative Data from Asymptomatic Nulliparous Women

OBJECTIVES: The muscles of the pelvic floor closest to the vaginal opening are subject to the greatest degree of stretch during vaginal childbirth. We aim to define normative quantitative EMG (QEMG) parameters for the pubovisceralis (PV) muscle in nulliparous women, and compare them to the external anal sphincter (EAS). METHODS: In 31 asymptomatic nulliparous women, concentric Needle EMG of the PV and the EAS was performed. Multi-motor unit action potential (Multi-MUAP) and interference pattern (IP) algorithms were utilized to obtain QEMG parameters. We used paired t-tests to compare PV and EAS parameters. RESULTS: The motor units for the PV were of greater duration (p < 0.002) and had more turns (p = 0.03) than the paired motor units in the EAS. The EAS demonstrated more turns/second (p = 0.02), greater activity (p = 0.01), and more short segments (p = 0.009) than the PV. CONCLUSIONS: The PV has longer and more complex motor units than the EAS. This knowledge continues to improve our ability to detect neuropathic changes in this vulnerable muscle area following childbirth or in women with pelvic floor dysfunction. In addition, the PV muscle group appears less responsive to requests for increased neuromuscular activity than the EAS. This needs to be further evaluated, as it may be associated with understanding which portion of the muscle functionally shortens to maintain the closure of the levator hiatus.

Fiber density of the motor units recruited at high and low force output

Motor units (MUs) are recruited according to the size principle. At low force output, macro-motor unit potentials (macro-MUPs) with small amplitude and area are recorded; MUs with large electrical size fire at high force output. Our objective was to elucidate whether this difference is caused by a higher fiber density (FD) of the MUs recruited at high force output. We measured the FD and respectively the amplitude and the area of the macro-MUPs via single-fiber macro electromyography (EMG) recorded at low and high force output in 48 healthy subjects. The macro-MUPs were significantly larger at high force output than at low force. The FD did not differ at the two force levels. Our findings suggest that the larger electrical size of the high recruitment threshold MUs is due not to a higher FD, but to a larger territory. FD is a robust EMG parameter, independent of the level of the force output.

Recruitment in retractor bulbi muscle during eyeblink conditioning: EMG analysis and common-drive model

To analyze properly the role of the cerebellum in classical conditioning of the eyeblink and nictitating membrane (NM) response, the control of conditioned response dynamics must be better understood. Previous studies have suggested that the control signal is linearly related to the CR as a result of recruitment within the accessory abducens motoneuron pool, which acts to linearize retractor bulbi muscle and NM response mechanics. Here we investigate possible recruitment mechanisms. Data came from simultaneous recordings of NM position and multiunit electromyographic (EMG) activity from the retractor bulbi muscle of rabbits during eyeblink conditioning, in which tone and periocular shock act as conditional and unconditional stimuli, respectively. Action potentials (spikes) were extracted and classified by amplitude. Firing rates of spikes with different amplitudes were analyzed with respect to NM response temporal profiles and total EMG spike firing rate. Four main regularities were revealed and quantified: 1) spike amplitude increased with response amplitude; 2) smaller spikes always appeared before larger spikes; 3) subsequent firing rates covaried for spikes of different amplitude, with smaller spikes always firing at higher rates than larger ones; and 4) firing-rate profiles were approximately Gaussian for all amplitudes. These regularities suggest that recruitment does take place in the retractor bulbi muscle during conditioned NM responses and that all motoneurons receive the same command signal (common-drive hypothesis). To test this hypothesis, a model of the motoneuron pool was constructed in which motoneurons had a range of intrinsic thresholds distributed exponentially, with threshold linearly related to EMG spike amplitude. Each neuron received the same input signal as required by the common-drive assumption. This simple model reproduced the main features of the data, suggesting that conditioned NM responses are controlled by a common-drive mechanism that enables simple commands to determine response topography in a linear fashion.

Dual simulated childbirth injuries result in slowed recovery of pudendal nerve and urethral function

AIMS

Pelvic floor muscle trauma and pudendal nerve injury have been implicated in stress urinary incontinence (SUI) development after childbirth. In this study, we investigated how combinations of these injuries affect recovery.

METHODS

Sixty-seven female Sprague-Dawley rats underwent vaginal distension (VD), pudendal nerve crush (PNC), PNC and VD (PNC + VD), pudendal nerve transection (PNT), or served as unmanipulated controls. Four days, 3 weeks, or 6 weeks after injury, we simultaneously recorded pudendal nerve motor branch potentials (PNMBP), external urethral sphincter electromyography (EUS EMG), and transurethral bladder pressure under urethane anesthesia. The presence of a guarding reflex (increased frequency and amplitude of PNMBP or EUS EMG activity) during leak point pressure (LPP) testing was determined.

RESULTS

Controls consistently demonstrated a guarding reflex. Four days after VD, EUS EMG activity was eliminated, but PNMBP activity reflected the guarding reflex; EUS EMG activity recovered after 3 weeks. Four days after PNC, both EUS EMG and PNMBP activity were eliminated, but demonstrated significant recovery at 3 weeks. Four days after PNC + VD both EUS EMG and nerve activity were eliminated, and little recovery was observed after 3 weeks with significant recovery of the guarding reflex 6 weeks after injury. Little recovery was observed at all time points after PNT. LPP results mirrored the reduction in EUS EMG activity.

CONCLUSION

Functional recovery occurs more slowly after PNC + VD than after either PNC or VD alone. Future work will be aimed at testing methods to facilitate neuroregeneration and recovery after this clinically relevant dual injury.

Quantitative measurements and analysis in electrodiagnostic studies: present and future

Electrodiagnostic studies (nerve conduction and needle electromyography) are powerful methods to study diseases of nerves and muscles. Conduction studies are performed to assess the continuity, anatomic course, excitability, number of axons and their synaptic connections, while needle electromyography examination is performed to assess the ‘electrical stability’ of the muscle fiber membrane, and the study of motor units (architecture, activation and number). We have reviewed the relationship between the quantitative measurements and the generators of the recorded potentials. Based on these relationships, the expected patterns of abnormalities for different pathologies are tabulated. This gives us a better appreciation of the sensitivity, specificity and usefulness of different tests when planning and conducting an electrodiagnostic examination. The limitations of current methods are indicated to suggest the need for future development.

Large motor units are selectively affected following a stroke

OBJECTIVE

Previous studies have revealed a loss of functioning motor units in stroke patients. However, it remained unclear whether the motor units are affected randomly or in some specific pattern. We assessed whether there is a selective loss of the large (high recruitment threshold) or the small (low recruitment threshold) motor units following a stroke.

METHODS

Forty-five stroke patients and 40 healthy controls participated in the study. Macro-EMG was recorded from the abductor digiti minimi muscle at two levels of force output (low and high). The median macro motor unit potential (macro-MUP) amplitude on the paretic side was compared with those on the unaffected side and in the controls.

RESULTS

In the control group and on the unaffected side, the macro-MUPs were significantly larger at the high force output than at the low one. However, on the paretic side the macro-MUPs at the high force output had the same amplitude as those recorded at the low force output. These changes correlated with the severity of the paresis.

CONCLUSIONS

Following a stroke, there is a selective functional loss of the large, high-threshold motor units. These changes are related to the severity of the symptoms.

SIGNIFICANCE

Our findings furnish further insight into the pathophysiology of the motor deficit following a stroke.

Quantitative anal sphincter electromyography in primiparous women with anal incontinence

OBJECTIVE

The purpose of this study was to determine whether evidence of denervation/reinnervation of the external anal sphincter is associated with anal incontinence symptoms immediately after delivery.

STUDY DESIGN

After a first vaginal delivery, 42 women completed an anal incontinence questionnaire. They also underwent concentric needle electromyography of the external anal sphincter. For each subject, motor unit action potential and interference pattern parameters were determined.

RESULTS

For the motor unit action potential, no difference was observed between patients with and without anal incontinence symptoms (t-test). For the interference pattern, the amplitude/turn was greater in subjects with fecal urgency (318 +/- 48 [SD] microV) and fecal incontinence (332 +/- 48 microV), compared with those without fecal urgency (282 +/- 38 microV) and fecal incontinence (286 +/- 41 microV; P = .02, t-test).

CONCLUSION

In this group of postpartum women with mild anal incontinence symptoms, interference pattern analysis shows evidence of denervation and subsequent reinnervation.

Determining the shape of the turns-amplitude cloud during anal sphincter quantitative EMG

We aimed to compare our normative data for quantitative interference pattern (IP) analysis of the anal sphincter to previously published data. In 28 nulliparous women, we performed IP analysis during quantitative concentric needle electromyography (QEMG) of the anal sphincter. At each sampling site, a 500-ms epoch was analyzed. The data were log transformed. Linear regression lines (with 95% confidence intervals) were calculated from the log transformed variables "turns-second" and "amplitude-turn." These confidence intervals were then transformed back into the original parameters to yield scatterplots with confidence curves. The mean turns-second were 203 (SD 174). The mean amplitude (mcv)-turn was 266 (SD 87). The regression coefficients for the log-transformed variables are constant = 1.5, slope = 0.3, and resultant cloud of raw data has a convex upper boundary. These appear slightly different than previously published reports, potentially influencing the determination of normal and abnormal studies.

Evidence from retractor bulbi EMG for linearized motor control of conditioned nictitating membrane responses

Classical conditioning of nictitating membrane (NM) responses in rabbits is a robust model learning system, and experimental evidence indicates that conditioned responses (CRs) are controlled by the cerebellum. It is unknown whether cerebellar control signals deal directly with the complex nonlinearities of the plant (blink-related muscles and peripheral tissues) or whether the plant is linearized to ensure a simple relation between cerebellar neuronal firing and CR profile. To study this question, the retractor bulbi muscle EMG was recorded with implanted electrodes during NM conditioning. Pooled activity in accessory abducens motoneurons was estimated from spike trains extracted from the EMG traces, and its temporal profile was found to have an approximately Gaussian shape with peak amplitude linearly related to CR amplitude. The relation between motoneuron activity and CR profiles was accurately fitted by a first-order linear filter, with each spike input producing an exponentially decaying impulse response with time constant of order 0.1 s. Application of this first-order plant model to CR data from other laboratories suggested that, in these cases also, motoneuron activity had a Gaussian profile, with time-of-peak close to unconditioned stimulus (US) onset and SD proportional to the interval between conditioned stimulus and US onsets. These results suggest that for conditioned NM responses the cerebellum is presented with a simplified "virtual" plant that is a linearized version of the underlying nonlinear biological system. Analysis of a detailed plant model suggests that one method for linearising the plant would be appropriate recruitment of motor units.

Experienced and physiological fatigue in neuromuscular disorders

OBJECTIVE

Fatigue has been described as a typical symptom of neurological diseases. It might be caused both by changes at the peripheral and at the central level. This study measured the level of experienced fatigue and physiological correlates of fatigue in three genetically defined neuromuscular disorders.

METHODS

Sixty-five facioscapulohumeral dystrophy (FSHD), 79 classical myotonic dystrophy (DM), 73 hereditary motor and sensory neuropathy type I (HMSN) patients and 24 age-matched healthy controls made a 2-min sustained maximal voluntary contraction of the biceps brachii muscle. Experienced fatigue at the current moment was assessed with the abbreviated fatigue questionnaire just before the physiological measurement. Peripheral fatigue was quantified by comparing the amplitudes of an initial and a final stimulated force response during rest. Muscle fibre conduction velocity was determined from a 5-channel surface EMG recording in order to show peripheral changes during the contraction. Central aspects of fatigue were measured using superimposed electrical endplate stimulation.

RESULTS

Patients showed an increased level of experienced fatigue. Total physiological and peripheral fatigue were smaller in patients compared to controls, and central fatigue was normal. The most interesting result of this study was the presence of a large central activation failure (CAF) in all groups of neuromuscular patients; they showed CAF values of 36-41% already directly at the start of sustained contraction, whereas the control group showed only 12%. CAF slightly correlated with the level of experienced fatigue just before the test.

CONCLUSIONS

The cause of the large CAF in patients is unclear. Reduced concentration, motivation or effort can lead to lower central activation. In neuromuscular patients especially fear of physical activity or fear to damage the muscle or nerve tissue may contribute. Besides, also physiological feedback mechanisms or changes at the motocortical level may be a cause of reduced central activation.

SIGNIFICANCE

For the clinician it is important to know that experienced fatigue is part of the clinical spectrum of neuromuscular patients. Besides, the weakness in these patients is aggravated by reduced central activation. Potentially, both problems could be subject of an intervention.

Singularity Characteristics of Needle EMG IP Signals

Clinical electromyography (EMG) interference pattern (IP) signals can reveal more diagnostic information than their constituents, the motor unit action potentials (MUAPs). Singularities and irregular structures typically characterize the mathematically defined content of information in signals. In this paper, a wavelet transform method is used to detect and quantify the singularity characteristics of EMG IP signals using the Lipschitz exponent (LE) and measures derived from it. The performance of the method is assessed in terms of its ability to discriminate healthy, myopathic and neuropathic subjects and how it compares with traditionally used Turns Analysis (TA) methods and a method recently developed by the authors, interscale wavelet maximum (ISWM). Highly significant intergroup differences were found using the LE method. Most of the singularity measures have a performance similar to that of ISWM and considerably better than that of TA. Some measures such as the ratio of the mean LE value to the number of singular points in the signal have considerably superior performance to both methods. These findings add weight to the view that wavelet analysis methods offer an effective way forward in the quantitative analysis of EMG IP signal to assist the clinician in the diagnosis of neuromuscular disorders.

[Current trends in the development of clinical electromyography]

<zakljucak> Kombinovana primena EMG tehnika uz pomoc kompjutera i standardizovanih softvera omogucava novi pristup u sagledavanju mikrofiziologije i mikropatologije MJ: od nivoa pojedinacnih misicnih vlakana (mikro EMG), preko njihove funkcije i anatomske strukture unutar jedne MJ (standardni EMG i skenirajuci EMG) do elektrofizioloskih karakteristika celokupne teritorije MJ u ispitivanom misicu (makro EMG) (slika 13). Navedene elektrofizioloske tehnike mogu da opisu fizioloski status MJ i pojedinacnih misicnih vlakana u vise detalja nego sto je to bilo moguce ranije koriscenjem samo standardne EMG. Ove tehnike pruzaju dragocenu pomoc ne samo u dijagnostici vec i u razumevanju patofizioloskih procesa koji se desavaju u NB.

Quantification of concentric-needle-induced insertional activity by turn/amplitude analysis

Quantification of needle-induced insertional activity (IA) by means of the turn/amplitude analysis (TAA) has not been attempted so far. IA was recorded from the right brachial biceps and right anterior tibial muscle of 29 healthy subjects, 17 woman, 12 men, aged 24-79 years and 51 patients with neuromuscular disorders (29 neuropathies and 22 myopathies), 24 woman, 27 men, aged 17-81 years. IA was analyzed with regard to IA duration (IAD), turns/second (T/S), amplitude/turn (A/T), T/S:IAD and A/T:IAD. IAD was not significantly different between healthy and diseased subjects in either of the two investigated muscles. On the contrary, T/S, A/T, T/S:IAD and A/T:IAD were significantly increased in the brachial biceps and anterior tibial muscle of patients with neuropathies. In myopathies T/S were increased in both muscles and the T/S:IAD in the anterior tibial muscle. Quantification of IA by TAA increases the sensitivity of conventional EMG from 38 to 69% in neuropathies and from 41 to 73% in myopathies. It is concluded that quantification of IA by TAA is of diagnostic support in the detection of neuromuscular disorders. The most useful parameter in this respect is the T/S, which, contrary to IAD, is increased in patients with neuropathies as well as patients with myopathies.

Quantitative electromyographic examination in myogenic disorders of 6 horses

Electromyographic needle examination (EMG), including the semiautomatic quantitative analysis of motor unit action potential (MUAP), is an important diagnostic tool for myopathy in humans. The diagnostic possibilities of this technique have not been fully explored in horses; however, recent studies have shown that MUAP analysis can be performed in conscious horses. To determine the diagnostic possibilities of EMG in horses, we compared the EMG results of the subclavian muscle, the triceps, and the lateral vastus muscle in 6 equine patients thought to have myogenic disorders with those in 7 normal control horses. The EMG results were compared with the results of the histopathologic examination of the lateral vastus muscle in patients and controls. Histopathologic examination showed muscle disease in 3 patients. In the patient group, several types of abnormal spontaneous activities were observed (mainly fibrillation potentials and positive sharp waves), and the MUAPs of the patient group had a markedly shorter duration and lower amplitude than those of the control group. In the subclavian muscle, triceps, and lateral vastus muscle of affected horses, the MUAP duration was 5.0 +/- 0.4 (mean +/- SD), 3.9 +/- 0.3, and 4.7 +/- 1.1 milliseconds, respectively. The MUAP amplitude was 217 +/- 55, 150 +/- 74, and 180 +/- 54 microV; the number of phases was 2.4 +/- 0.2, 2.5 +/- 0.3, and 2.3 +/- 0.1; and the number of turns was 2.6 +/- 0.2, 2.4 +/- 0.2, and 2.8 +/- 0.5, respectively. In conclusion, it appears that the EMG may be a more sensitive method than other techniques for examining muscle biopsies for diagnosis of early-stage myopathy in horses.

Quantitative motor unit action potential analysis of skeletal muscles in the Warmblood horse

Motor unit action potential (MUP) analysis in human medicine is a valuable and important diagnostic technique enabling discrimination between myogenic and neurogenic problems. This study establishes normative data in subclavian, triceps and lateral vastus muscles for clinical application of MUP analysis in the Warmblood horse, and examines whether muscle differences are present. Electromyographic (EMG) needle examination and MUP analysis were performed of the triceps, lateral vastus and subclavian muscles in 7 awake, nonsedated, Warmblood horses age 4-10 years. The amplitude, duration, number of phases and turns were calculated from the recorded superimposed MUPs together with intramuscular and rectal temperatures. No significant differences were found in duration of insertional activity between the 3 muscles. The mean +/- s.d. duration of the insertional activity was 526 +/- 1483 ms. The MUP amplitude of all 3 muscles differed significantly, with the highest amplitude (427 +/- 3.20 microV) in the triceps and the lowest (220 +/- 2.08 microV) in the subclavian muscle. The number of turns of the lateral vastus (3.0 +/- 1.22) was significantly higher than that of the triceps muscle (2.7 +/- 1.51). No differences were found in MUP duration (5.9-6.4 ms).

Interscale wavelet maximum-a fine to coarse algorithm for wavelet analysis of the EMG interference pattern

A method has been developed, interscale wavelet maximum (ISWM), for characterising the electromyogram (EMG) interference pattern to assist in the diagnosis of neuromuscular disease. EMG signals are decomposed with the redundant dyadic wavelet transform and wavelet maxima (WM) are found. Thresholding methods are applied to remove WM due to noise and background activity. An efficient fine-to-coarse algorithm identifies the WM tree structure for the motor unit action potential rising edges. The WM for each tree are summed at each scale; the largest value is the ISWM. Highly significant differences in ISWM values have been found between healthy, myopathic, and neuropathic subjects that could make the technique a useful diagnostic tool.

Quantitative analysis of motor unit action potentials in the subclavian muscle of healthy horses

OBJECTIVE

To evaluate the application of analysis of motor unit action potentials (MUAP) in horses and to obtain values of MUAP for the subclavian muscle of horses.

ANIMALS

10 healthy adult Dutch Warmblood horses.

PROCEDURE

Electromyographic examination of the subclavian muscle in conscious nonsedated horses was performed to evaluate insertional activity, spontaneous activity, MUAP variables, and recruitment patterns. Muscle and body temperatures were measured at the beginning and end of the procedure. Amplitude, duration, number of phases, and number of changes in direction (ie, turns) for all representative MUAP were analyzed to determine values for this muscle in this group of horses.

RESULTS

Mean +/- SD duration of insertional activity was 471.7 +/- 33.45 milliseconds. Mean MUAP amplitude in the examined horses was 379 RV (95% confidence interval [CI], 349 to 410 microV). Mean MUAP duration of the subclavian muscle was 727 milliseconds (95% CI, 6.84 to 7.71 milliseconds). Mean number of phases was 2.9, and mean number of turns was 3.0. Prevalence of polyphasic MUAP defined as MUAP with > 4 phases, was 77%. Number of MUAP that had > 5 turns was 2.4%. Satellite potentials were found in 1.0% of the MUAP CONCLUSIONS AND CLINICAL RELEVANCE: This study revealed that electromyography including MUAP analysis can be performed in horses, and values for the subclavian muscle in healthy adult horses can be obtained. Analysis of MUAP could be a valuable diagnostic tool for use in discriminating between myogenic and neurogenic problems in horses.

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.

Pelvic muscle electromyography of levator ani and external anal sphincter in nulliparous women and women with pelvic floor dysfunction

OBJECTIVE

The purpose of this study was to compare results of electromyographic assessment of muscular recruitment between nulliparous control subjects without pelvic floor dysfunction and parous subjects with genuine stress urinary incontinence and with pelvic organ prolapse. Interference pattern analysis is an electromyographic technique that reproducibly measures muscular recruitment by detecting both "turns" in the electromyographic signal produced by positive and negative peaks of the motor unit potentials and motor unit potential amplitude. Fewer turns can indicate loss of motor units or failure of central activation of contraction, whereas greater amplitude can indicate reinnervation after nerve damage.

STUDY DESIGN

We performed concentric needle electrode electromyographic examinations of the levator ani and external anal sphincter in 15 nulliparous control subjects and 20 parous subjects with abnormalities (n = 9 with genuine stress urinary incontinence, n = 11 with stage III or IV pelvic organ prolapse). We made digital recordings at multiple sites at rest and with moderate and maximal contraction. Interference pattern analysis yielded the number of turns per second and the mean signal amplitude (in microvolts) for each site at each contraction level. We compared individual patient data with data from the healthy population by means of cloud analysis. Mean values of number of turns per second and mean amplitude in each group were then compared with nonparametric methods and regression models.

RESULTS

Mean ages were 28.7 years (range, 20-49 years) for the control group, 54.3 years (range, 35-75 years) for subjects with genuine stress urinary incontinence, and 65 years (range, 41-77 years) for subjects with pelvic organ prolapse. Median clinical levator ani strengths were 9 (range, 5-9) in the control group, 5 (range, 2-7) in the genuine stress urinary incontinence group, and 5 (range, 2-8) in the pelvic organ prolapse group. Median external anal sphincter strengths were 9 (range, 7-9) in the control group, 5 (range, 3-9) in the genuine stress urinary incontinence group, and 8 (range, 4-9) in the pelvic organ prolapse group. The external anal sphincters of subjects with pelvic organ prolapse had the highest percentage of abnormal study results according to cloud analysis. Mean number of turns per second in levators was greater in control subjects than in subjects with abnormalities (P =.034). We found similar differences in number of turns per second for the external anal sphincter (P =.004). In contrast, we did not find differences between groups in mean amplitude in either the levator ani or the external anal sphincter. Comparison of patients with genuine stress urinary incontinence versus subjects with pelvic organ prolapse showed no significant difference in the number of turns per second in either muscle. Mean amplitude was greater in the pelvic organ prolapse group than in the genuine stress urinary incontinence group for both muscles (levator ani, P =.028; external anal sphincter, P =.048). Neither mean amplitude nor the number of turns per second could be predicted by clinically estimated levator ani strength, age, or fecal incontinence.

CONCLUSION

Compared with nulliparous control subjects, patients with genuine stress urinary incontinence and pelvic organ prolapse had changes in the levator ani and external anal sphincter consistent with either motor unit loss or failure of central activation, or both. Subjects with pelvic organ prolapse had findings consistent with greater recovery than was found in those with genuine stress urinary incontinence. Measures of recruitment by interference pattern analysis correlated better with clinical external anal sphincter strength than with levator ani strength and were independent of age.

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.