Generative Multiple-Instance Learning Models For Quantitative Electromyography

We present a comprehensive study of the use of generative modeling approaches for Multiple-Instance Learning (MIL) problems. In MIL a learner receives training instances grouped together into bags with labels for the bags only (which might not be correct for the comprised instances). Our work was motivated by the task of facilitating the diagnosis of neuromuscular disorders using sets of motor unit potential trains (MUPTs) detected within a muscle which can be cast as a MIL problem. Our approach leads to a state-of-the-art solution to the problem of muscle classification. By introducing and analyzing generative models for MIL in a general framework and examining a variety of model structures and components, our work also serves as a methodological guide to modelling MIL tasks. We evaluate our proposed methods both on MUPT datasets and on the MUSK1 dataset, one of the most widely used benchmarks for MIL.Comment: Appears in Proceedings of the Twenty-Ninth Conference on Uncertainty in Artificial Intelligence (UAI2013

Assessing motor deficits in compressive neuropathy using quantitative electromyography

<p>Abstract</p> <p>Background</p> <p>Studying the changes that occur in motor unit potential trains (MUPTs) may provide insight into the extent of motor unit loss and neural re-organization resulting from nerve compression injury. The purpose of this study was to determine the feasibility of using decomposition-based quantitative electromyography (DQEMG) to study the pathophysiological changes associated with compression neuropathy.</p> <p>Methods</p> <p>The model used to examine compression neuropathy was carpal tunnel syndrome (CTS) due to its high prevalence and ease of diagnosis. Surface and concentric needle electromyography data were acquired simultaneously from the abductor pollicis brevis muscle in six individuals with severe CTS, eight individuals with mild CTS and nine healthy control subjects. DQEMG was used to detect intramuscular MUPTs during constant-intensity contractions and to estimate parameters associated with the surface- and needle-detected motor unit potentials (SMUPs and MUPs, respectively). MUP morphology and stability, SMUP morphology and motor unit number estimates (MUNEs) were compared among the groups using Kruskal-Wallis tests.</p> <p>Results</p> <p>The severe CTS group had larger amplitude and longer duration MUPs and smaller MUNEs than the mild CTS and control groups, suggesting that the individuals with severe CTS had motor unit loss with subsequent collateral reinnervation, and that DQEMG using a constant-intensity protocol was sensitive to these changes. SMUP morphology and MUP complexity and stability did not significantly differ among the groups.</p> <p>Conclusions</p> <p>These results provide evidence that MUP amplitude parameters and MUNEs obtained using DQEMG, may be a valuable tool to investigate pathophysiological changes in muscles affected by compressive motor neuropathy to augment information obtained from nerve conduction studies. Although there were trends in many of these measures, in this study, MUP complexity and stability and SMUP parameters were, of limited value.</p

Near-Fiber Electromyography

ObjectiveDescribe and evaluate the concepts of near fiber electromyography (NFEMG), the features used, including near fiber motor unit potential (NFMUP) duration and dispersion, which relate to motor unit distal axonal branch and muscle fiber conduction time dispersion, and NFMUP segment jitter, a new measure of the temporal variability of neuromuscular junction transmission (NMJ), and axonal branch and muscle fibre conduction for the near fibres (i.e. NF jitter), and the methods for obtaining their values.MethodsTrains of high-pass filtered motor unit potentials (MUPs) (i.e. NFMUP trains) were extracted from needle-detected EMG signals to assess changes in motor unit (MU) morphology and electrophysiology caused by neuromuscular disorders or ageing. Evaluations using simulated needle-detected EMG data were completed and example human data are presented.ResultsNFEMG feature values can be used to detect axonal sprouting, conduction slowing and NMJ transmission delay as well as changes in MU fiber diameter variability, and NF jitter. These changes can be detected prior to alterations of MU size or numbers.ConclusionsThe evaluations clearly demonstrate and the example data support that NFMUP duration and dispersion reflect MU distal axonal branching, conduction slowing and NMJ transmission delay and/or MU fiber diameter variability and that NFMUP jiggle and segment jitter reflect NF jitter

Effects of Aging on Genioglossus Motor Units in Humans

The genioglossus is a major upper airway dilator muscle thought to be important in obstructive sleep apnea pathogenesis. Aging is a risk factor for obstructive sleep apnea although the mechanisms are unclear and the effects of aging on motor unit remodeled in the genioglossus remains unknown. To assess possible changes associated with aging we compared quantitative parameters related to motor unit potential morphology derived from EMG signals in a sample of older (n = 11; >55 years) versus younger (n = 29; <55 years) adults. All data were recorded during quiet breathing with the subjects awake. Diagnostic sleep studies (Apnea Hypopnea Index) confirmed the presence or absence of obstructive sleep apnea. Genioglossus EMG signals were analyzed offline by automated software (DQEMG), which estimated a MUP template from each extracted motor unit potential train (MUPT) for both the selective concentric needle and concentric needle macro (CNMACRO) recorded EMG signals. 2074 MUPTs from 40 subjects (mean±95% CI; older AHI 19.6±9.9 events/hr versus younger AHI 30.1±6.1 events/hr) were extracted. MUPs detected in older adults were 32% longer in duration (14.7±0.5 ms versus 11.1±0.2 ms; P = 0.05), with similar amplitudes (395.2±25.1 µV versus 394.6±13.7 µV). Amplitudes of CNMACRO MUPs detected in older adults were larger by 22% (62.7±6.5 µV versus 51.3±3.0 µV; P<0.05), with areas 24% larger (160.6±18.6 µV.ms versus 130.0±7.4 µV.ms; P<0.05) than those detected in younger adults. These results confirm that remodeled motor units are present in the genioglossus muscle of individuals above 55 years, which may have implications for OSA pathogenesis and aging related upper airway collapsibility

The relationship between ciliary neurotrophic factor (CNTF) genotype and motor unit physiology: preliminary studies

BACKGROUND: Ciliary neurotrophic factor (CNTF) is important for neuronal and muscle development, and genetic variation in the CNTF gene has been associated with muscle strength. The effect of CNTF on nerve development suggests that CNTF genotype may be associated with force production via its influence on motor unit size and firing patterns. The purpose of this study is to examine whether CNTF genotype differentially affects motor unit activation in the vastus medialis with increasing isometric force during knee extension. RESULTS: Sixty-nine healthy subjects were genotyped for the presence of the G and A (null) alleles in the CNTF gene (n = 57 G/G, 12 G/A). They were tested using a dynamometer during submaximal isometric knee extension contractions that were from 10–50% of their maximal strength. During the contractions, the vastus medialis was studied using surface and intramuscular electromyography with spiked triggered averaging to assess surface-detected motor unit potential (SMUP) area and mean firing rates (mFR) from identified motor units. CNTF genotyping was performed using standard PCR techniques from DNA obtained from leucocytes of whole blood samples. The CNTF G/A genotype was associated with smaller SMUP area motor units and lower mFR at higher force levels, and fewer but larger units at lower force levels than G/G homozygotes. The two groups used motor units with different size and activation characteristics with increasing force generation. While G/G subjects tended to utilize larger motor units with increasing force, G/A subjects showed relatively less increase in size by using relatively larger units at lower force levels. At higher force levels, G/A subjects were able to generate more force per motor unit size suggesting more efficient motor unit function with increasing muscle force. CONCLUSION: Differential motor unit responses were observed between CNTF genotypes at force levels utilized in daily activities

Relationship of anabolic hormones with motor unit characteristics in quadriceps muscle in healthy and frail ageing men

ContextAnabolic hormones are important factors in maintaining muscle mass for ageing men, but their role in overall motor unit structure and function is unclear.ObjectiveTo determine associations of anabolic and reproductive hormone levels with motor unit characteristics in quadriceps muscle in older healthy and frail men.DesignObservational cohort study of community dwelling men.ParticipantsHealthy and frail men > 65 years old.InterventionNone.Outcome measureQuantitative assessments of electromyography-derived motor unit potential size (MUP) and compound muscle action potential size (CMAP) of vastus lateralis muscle.ResultsWe studied 98 men (mean±SD: age 73±6 years; BMI 25.7±4.0 kg/m2; diabetes 11%) of whom 45% were prefrail and 18% frail. After adjusting for age, BMI and prevalent diabetes, higher total and free testosterone levels were significantly related to larger CMAP (total testosterone: β (95% CI): 0.3 (0.08, 0.53); free testosterone: 0.34 (0.13, 0.56)). Exploratory analysis showed the relationship between free testosterone and CMAP was stronger in frail rather than robust men. In univariate analyses, estradiol was associated with CMAP size (0.37 (0.16, 0.57)); and vitamin D was associated with MUP size (0.22 (0.01, 0.43)) but these relationships were no longer significant after adjusting for potential confounders.ConclusionOur data highlight the associations between androgen levels and the electrophysiological characteristics of older men, particularly in the frail. Clinical trials involving administration of androgens will help to elucidate the potential benefits of intervention on neuromuscular function and/or frailty status

Frailty phenotype and frailty index are associated with distinct neuromuscular electrophysiological characteristics in men

The purpose of this study was to determine whether neuromuscular electrophysiological characteristics that are known to underlie sarcopenia are also associated with the more complex frailty syndrome. Eighty‐six men [mean (SD) age, 74 (8) years] were classed as non‐frail (robust), prefrail or frail using criteria from the frailty phenotype (FP) and the frailty index (FI). The femoral nerve was stimulated maximally and the resulting compound muscle action potential amplitude (CMAP) measured over the vastus lateralis. Motor unit potential (MUP) size was assessed during voluntary contractions using intramuscular electromyography (iEMG). Logistic and negative binomial regression models determined relationships between FP and FI with CMAP and MUP sizes before and after adjustments for age and body mass index. Larger CMAP size was associated with a lower likelihood of frailty in fully adjusted models: a 1SD higher level in vastus lateralis CMAP size was associated with a 0.4 (95% confidence interval: 0.2, 0.6; P < 0.01) unit lower FI (40% of the FI range) and more than halving of the odds [odds ratio: 0.43 (95% confidence interval: 0.21, 0.90)] of having a frail/prefrail phenotype. Greater MUP size was also related to lower FI values using unadjusted and fully adjusted models. However, MUP size was not significantly related to FP in any model. Smaller MUPs and a smaller CMAP were significantly associated with a higher likelihood of frailty, independent of age and body mass index. These results relate neuromuscular electrophysiological characteristics to the complex frailty syndrome and identify motor unit remodelling as a possible contributing factor