Search PubMed⌕ Search

Biomedical subjects

J Duchêne

Publications and source records attributed to J Duchêne.

16 recordsLinked to original sources
PubMed2001

Surface electromyography analysis in long-term recordings: application to head rest comfort in cars.

Analysis of long-term surface electromyographic (SEMG) signals has many applications in ergonomics when related to muscle fatigue. The present work proposes a set of processing methods reporting SEMG modifications during long-term driving tests in various situations (with or without head rest). A segmentation/classification algorithm allows signal splitting into homogeneous parts (postural activity and EMG bursts) and an efficient artefact suppression. Postural activity modifications are evaluated from time-varying amplitude probability density function (TAPDF) parameters. EMG burst analysis is achieved taking into account the relationships of these bursts with accelerometric events. This segmentation/classification procedure improves repeatability but does not significantly modify the overall results obtained before segmentation, as far as the analysis of head rest influence is concerned.

Algorithms↗
PubMed2000

Experimental study of suspension-feeding activity in the serpulid polychaete Ditrupa arietina (O.F. Müller).

As time spent feeding can be an index of the feeding intensity, we attempted to describe the filtering activity in the suspension-feeding polychaete Ditrupa arietina. This description was based on the detection of the opening of the gill-crown by an automated image analysis system. The common pattern of activity could be described as the succession of filtering events and resting periods of which the number and the mean duration differed greatly from one worm to another. Filtering activity in D. arietina was neither a continuous process nor even a process having a particular rhythm. Within a same batch of worms, total filtration durations could represent between 12.5 and 87.5% of the total experimental time. Despite a strong inter-individual variability, our results showed the existence of pronounced seasonal variations in the activity of the gill-crown. In May, worms spent less than 25% of time feeding compared to more than 50% during the rest of year. These temporal changes appeared to result from the physiological state of the worms (reproductive period and ageing) at the time of the experiment.

Journal Article↗
PubMed2000

A model of EMG generation.

Simulation models are unavoidable in experimental research when the point is to develop new processing algorithms to be applied on real signals in order to extract specific parameter values. Such algorithms have generally to be optimized by comparing true parameter values to those deduced from the algorithm. Only a simulation model can allow the user to access and control the actual process parameter values. This constraint is especially true when dealing with biomedical signals like surface electromyogram (SEMG). This work is an attempt to produce an efficient SEMG simulation model as a help for assessing algorithms related to SEMG features description. It takes into account the most important parameters which could influence these characteristics. This model includes all transformations from intracellular potential to surface recordings as well as a fast implementation of the extracellular potential computation. In addition, this model allows multiple graphically-programmable electrode-set configurations and SEMG simulation in both voluntary and elicited contractions.

Action Potentials↗
PubMed2000

Uterine EMG analysis: a dynamic approach for change detection and classification.

Toward the goal of detecting preterm birth by characterizing events in the uterine electromyogram (EMG), we propose a method of detection and classification of events in this signal. Uterine EMG is considered as a nonstationary signal and our approach consists of assuming piecewise stationarity and using a dynamic change detector with no a priori knowledge of the parameters of the hypotheses on the process state to be detected. The detection approach is based on the dynamic cumulative sum (DCS) of the local generalized likelihood ratios associated with a multiscale decomposition using wavelet transform. This combination of DCS and multiscale decomposition was shown to be very efficient for detection of both frequency and energy changes. An unsupervised classification based on the comparison between variance-covariance matrices computed from selected scales of the decomposition was implemented after detection. Finally a class labeling based on neural networks was developed. This algorithm of detection-classification-labeling gives satisfactory results on uterine EMG: in most cases more than 80% of the events are correctly detected and classified whatever the term of gestation.

Algorithms↗
PubMed1998

Variability of some SEMG parameter estimates with electrode location.

Muscular action potential conduction velocity (CV) and mean power frequency (MPF) are commonly used parameters to describe the surface electromyographic signal (SEMG). The discrepancies concerning the behavior and interpretation of these main parameters in the literature have motivated this work. Our objective was to evaluate within- and between-individual reproducibility, sensitivity and variation of CV and MPF depending on the electrode location with respect to various contraction modalities. The results present evidence for significant influence of electrode location on CV and MPF, not only in their initial values but also in their changes during fatiguing efforts. This influence appears to be subject-dependent. This variability seems to be essentially due to the relative displacements of myotendinous and neuromuscular junctions with respect to the electrode set. Moreover, this study shows that MPF can be seen as force-dependent under certain conditions and that the CV-MPF relationship is strongly influenced by methodological factors. In conclusion, it seems irrelevant to derive reliable SEMG parameter estimates without considering electrode location. There is a strong need for proper standardization based on anatomical and methological aspects before attempting any individual characterization. Finally, we suggest a procedure for assessment of measurement quality.

Action Potentials↗
PubMed1996

Reproducibility of kinetics of electromyogram spectrum parameters during dynamic exercise.

During incremental exercise on a cycle ergometer a study was made of the reproducibility of changes in electromyographic activity (EMG) of human quadriceps muscles. Seven subjects performed three periods of incremental exercise either every 2 weeks (G1: four subjects) or 6 weeks (G2: three subjects). Each test was normalized with respect to the maximal aerobic power (MAP) of the subject. It consisted of a quasilinear increase in mechanical power (from 20% to 100% MAP) during 8 min. For rectus femoris muscle activity, changes in total power spectrum (PEMG) and in mean power frequency (MPF) were fitted by a 3rd order polynomial function (named profile) and normalized with respect to the maximal value for PEMG and to the mean value for MPF. A curvilinear increase was found for PEMG. The MPF kinetics varied from one subject to another. These changes were either a continuous increase, or a continuous decrease, or an increase followed by a decrease. Only for G2, was MAP determined before each test in order to update the limits of the test. A good reproducibility of PEMG was shown by its mean magnitude [95.88%, (SD 3.92)] and by computing a mean correlation coefficient between profiles two by two [r2 = 0.948 (SD 0.028) n = 21]. Intraclass coefficient correlation (ICC) calculated for each subject indicated a high level of reproducibility for five of the seven subjects (ICC > 0.80). No clear effect of MAP updating on PEMG and MPF profile reproducibility was observed. Thus it is suggested that MPF kinetics may characterize a subject at a given moment while PEMG kinetics may illustrate a normal profile, and they may both characterize EMG changes for a population during incremental exercise.

Adult↗
PubMed1996

Uterine EMG spectral analysis and relationship to mechanical activity in pregnant monkeys.

The objective is to analyse internal and external recordings of uterine EMG in order to reveal common features and to assess the relationship between electrical activity and intra-uterine pressure modification. Three monkeys participated in the study, one as a reference and the others for data. EMGs are recorded simultaneously, internally by unipolar wire electrodes and externally by bipolar Ag/AgCl electrodes. Intra-uterine pressure is recorded as a mechanical index. Except for delay measurements, parameters are derived from spectral analysis and relationships between recordings are assessed by studying the coherence. Spectral analysis exhibits two basic activities in the analysed frequency band, and frequency limits are defined as relevant parameters for electrical activity description. Parameter values do not depend on the internal electrode location. Internal and external EMGs present a similar spectral shape, despite differences in electrode configuration and tissue filtering. It is deduced that external uterine EMG is a good image of the genuine uterine electrical activity. To some extent, it can be related to an average cellular electrical activity.

Animals↗
PubMed1996

Surface electromyography as a tool to study the head rest comfort in cars.

In this study, two methods were presented in order to evaluate objectively the comfort of head rests in cars using surface electromyography (SEMG). First, the Amplitude Probability Density Function (APDF) was computed. Extremely low level intensity activities were measured. No significant differences were observed on SEMG global activity between experiments with and without a head rest. Second, instead of computing one APDF, several APDF were calculated over time. Analyses focused on the rate of evolution of APDF parameters. This was a time varying APDF (TAPDF). This last method allowed a better diagnosis than the first one. For drivers, significant decreases in SEMG activity were observed when using a head rest. For passengers, a contradictory increase in SEMG activity was observed during experiments with a head rest. This observation was explained by the seat back angle chosen by passengers.

Arousal↗
PubMed1996

Processing visual evoked potentials based on matched filtering of single trial responses.

Physiological signals recorded after presentation of a stimulus can be considered as the sum of an evoked sensory response and uncorrelated noise corresponding to the spontaneous neural background activity. In case of low signal-to-noise ratio, the sensory signal is estimated by averaging a large number of single trial records sampled under the same experimental conditions. The averaging technique, however, is inappropriate for displaying trial-to-trial variations that may occur during a recording session. A method based on matched filtering was developed for processing single visual evoked potentials (VEPs). To illustrate the performance of this method, a set of VEPs for grating patches of 8 different contrasts (including 0) was evaluated. The VEPs were subjected to signal detection analysis by computing for each contrast similarity indices between the single trial records and the averaged response used as a template. The signals were analysed in terms of probability density distributions, expressing the goodness of fit between template and each single waveform.

Cluster Analysis↗
PubMed1993

MicroPACS: a PC-based small PACS implementation.

To make picture archiving and communication systems (PACS) a practical reality for small-scale structures, it appears necessary to build a network that integrates and optimises production management, analysis and storage of images, and to include the ability to communicate with other similar remote structures. To solve the various technical problems related to small-scale PACS implementation, MicroPACS, a local area network, was developed around PC-like microcomputers. Every necessary function is assessed and implemented, including a centralised data-base, a distributed image bank, different storage levels and a specific task for image exchanges. An additional protocol was also developed for remote consultation through ISDN. Standardisation of image encapsulation and a point-to-point link between remote sites ensure easy transfers between heterogeneous local networks or bases and integrity of local databases.

Computer Communication Networks↗
PubMed1993

Uterine electromyography: a critical review.

On the basis of a literature review, this work summarizes uterine animal and human electromyographic information obtained at cellular, myometrial, and abdominal levels during gestation and parturition. We show that both internal and external electromyograms occur in phase with intrauterine pressure increase and exhibit similar spectra, including a slow wave (0.01 < frequency < 0.03 Hz) probably because of mechanical artifacts and a fast wave whose frequency content can be subdivided into a low-frequency band always present in every contraction and a high-frequency band related to efficient parturition contractions. Application of classic spectral techniques to electromyogram envelopes has identified group propagation but not pacemaker areas. However, no time delay or classic propagation has been demonstrated by applying the same spectral techniques to the electromyogram itself, probably because of the nonlinearity and three-dimensional nature of the propagating process.

Animals↗
PubMed1993

Surface electromyogram during voluntary contraction: processing tools and relation to physiological events.

Surface electromyography (SEMG) has been used extensively in the last years in a variety of applications, including muscle function assessment, pathology identification, ergonomics, pattern analysis, or population characterization. Advanced processing methods, especially in the spectral domain, provide the research worker with more and more precise and user-friendly tools for signal characterization, analysis, and classification. The use of such sophisticated tools requires many assumptions on signal characteristics, and the wide variety of computing options related to each processing method makes it difficult to compare the results of different works when these options are omitted in the reports or improperly applied. This work first aims at taking stock of the various processing methods which have emerged in the last years around surface electromyography: signal acquisition, random feature extraction, time and spectral parameter determination, statistical tests application. The main methods are briefly explained and discussed, then variations between apparently equivalent methods are pointed out, necessary hypotheses are underlined, and the use of such methods in SEMG processing is shown with respect to the more recent works. A second section shows how authors deal with parameters extracted from SEMG in order to relate them to physiological modifications (force, fiber type, fiber environment).

Adult↗
PubMed1990

Electromyogram power spectrum during dynamic contractions at different intensities of exercise.

During dynamic contractions performed on a cycle ergometer, we studied the influence of motor unit (MU) recruitment on the electromyographic (EMG) spectral content by exerting mechanical power of different intensities, which was chosen to remain below the maximal aerobic power (VO2max). The spectral parameters: EMG total power (PEMG), mean (MPF) and median (MED) power frequencies, which are the most representative of the EMG spectral content, were calculated according to the EMG activity of the vastus medialis muscle (VM) and soleus muscle (SOL) of the right leg. For VM and SOL, PEMG increased linearly with exerted power demonstrating an enhancement of MU recruitment. Moreover these relationships were less scattered when exerted power was expressed as a percentage of VO2max. Changes in MPF and MED with varying exercise intensities were different from one subject to another. For a set of subjects, MPF and MED were found to be independent of exerted power. Although VM and SOL muscles are different in fibre type composition, similar results were obtained for both EMG activities. We have concluded that for dynamic contractions performed at different intensities below VO2max, the recruitment of the MU has a poor effect on the EMG spectral content whatever the predominant type of fibre.

Adult↗
PubMed1990

EMG spectral shift as an indicator of fatigability in an heterogeneous muscle group.

Changes in electromyogram (EMG) power spectra were investigated in the triceps surae muscles of two classes of individuals (untrained subjects and athletes) maintaining a plantarflexion torque of 80% of maximal voluntary contraction until exhaustion. A set of 23 parameters describing changes in the frequency content and power of EMG was defined. For most experiments, classical changes were found, indicating a shift of the EMG spectra towards lower frequencies and an increase in the total power of the signals. In 12% of the experiments, alternations in activity between synergistic muscles were found, leading to a large variability in the spectral parameters. After the expression of each experiment in terms of a reduced data matrix and matrix to vector transformations, three methods of discrimination were used to classify subjects with respect to changes in the EMG signal during sustained contraction: (1) evaluation of the most discriminating parameter, (2) principal components analysis, (3) transformation maximizing differences between classes. Method (3) was found to be preferable since it led to good separation of the two classes in a reference group of subjects and a satisfactory projection of each individual from a group of unknowns into the appropriate class. These results suggest using a method such as this for ergonomic or athletic training purposes rather than the usual method of monitoring the frequency shift of the EMG.

Adult↗