Denoising of HD-sEMG signals using canonical correlation analysis.

High-density surface electromyography (HD-sEMG) is a recent technique that overcomes the limitations of monopolar and bipolar sEMG recordings and enables the collection of physiological and topographical informations concerning muscle activation. However, HD-sEMG channels are usually contaminated by noise in an heterogeneous manner. The sources of noise are mainly power line interference (PLI), white Gaussian noise (WGN) and motion artifacts (MA). The spectral components of these disruptive signals overlap with the sEMG spectrum which makes classical filtering techniques non effective, especially during low contraction level recordings. In this study, we propose to denoise HD-sEMG recordings at 20 % of the maximum voluntary contraction by using a second-order blind source separation technique, named canonical component analysis (CCA). For this purpose, a specific and automatic canonical component selection, using noise ratio thresholding, and a channel selection procedure for the selective version (sCCA) are proposed. Results obtained from the application of the proposed methods (CCA and sCCA) on realistic simulated data demonstrated the ability of the proposed approach to retrieve the original HD-sEMG signals, by suppressing the PLI and WGN components, with high accuracy (for five different simulated noise dispersions using the same anatomy). Afterward, the proposed algorithms are employed to denoise experimental HD-sEMG signals from five healthy subjects during biceps brachii contractions following an isometric protocol. Obtained results showed that PLI and WGN components could be successfully removed, which enhances considerably the SNR of the channels with low SNR and thereby increases the mean SNR value among the grid. Moreover, the MA component is often isolated on specific estimated sources but requires additional signal processing for a total removal. In addition, comparative study with independent component analysis, CCA-wavelet and CCA-empirical mode decomposition (EMD) proved a higher efficiency of the presented method over existing denoising techniques and demonstrated pointless a second filtering stage for denoising HD-sEMG recordings at this contraction level.

Extraction of the brachialis muscle activity using HD-sEMG technique and canonical correlation analysis.

The Brachialis (BR) is placed under the Biceps Brachii (BB) deep in the upper arm. Therefore, the detection of the corresponding surface Electromyogram (sEMG) is a complex task. The BR is an important elbow flexor, but it is usually not considered in the sEMG based force estimation process. The aim of this study was to attempt to separate the two sEMG activities of the BR and the BB by using a High Density sEMG (HD-sEMG) grid placed at the upper arm and Canonical Component Analysis (CCA) technique. For this purpose, we recorded sEMG signals from seven subjects with two 8 × 4 electrode grids placed over BB and BR. Four isometric voluntary contraction levels were recorded (5, 10, 30 and 50 %MVC) for 90° elbow angle. Then using CCA and image processing tools the sources of each muscle activity were separated. Finally, the corresponding sEMG signals were reconstructed using the remaining canonical components in order to retrieve the activity of the BB and the BR muscles.

CXCL13 and CCL11 Serum Levels and Lymphoma and Disease Activity in Primary Sjögren's Syndrome.

OBJECTIVE: Non-Hodgkin's lymphoma (NHL) is a severe complication of primary Sjögren's syndrome (SS). Ectopic germinal centers (GCs) in the salivary glands are predictors of the occurrence of NHL. Given the association between CCL11 and CXCL13 and ectopic GCs, we assessed the link between these chemokines and NHL, as well as the association between these chemokines and disease activity, in patients with primary SS. METHODS: Serum levels of CCL11 and CXCL13 were evaluated by multiplex assay in 385 patients included in the Assessment of Systemic Signs and Evolution of Sjögren's Syndrome (ASSESS) cohort. The association between chemokine levels, B cell biomarkers, and patient subsets was assessed using Spearman's test for continuous data and the nonparametric Mann-Whitney U test for categorical data. Multivariate analyses were performed to identify parameters associated with lymphoma and disease activity. RESULTS: Seventeen patients had a history of lymphoma, and 5 of them had developed NHL during followup. The median serum levels of CCL11 and CXCL13 in the total cohort were 106.48 pg/ml (interquartile range 69.33-149.85) and 108.31 pg/ml (interquartile range 58.88-200.13), respectively. Patients with lymphoma had higher levels of CXCL13 than did patients without lymphoma (P = 0.006) and a trend toward a higher level of CCL11 (P = 0.056). Low C4 and high BAFF levels were associated with NHL on multivariate analysis (P = 0.01 and P = 0.0002, respectively). CCL11 and CXCL13 levels correlated positively with the rheumatoid factor titer, the κ-to-λ free light chain ratio, and the ß2 -microglubulin level. CXCL13 was the only parameter associated with disease activity on multivariate analysis. CONCLUSION: These findings demonstrate a link between CXCL13 and CCL11 and disease activity and lymphoma. This highlights the continuum between chronic B cell activation, disease activity, and lymphomagenesis in patients with primary SS.

Evaluation of muscle force classification using shape analysis of the sEMG probability density function: a simulation study.

In this work, we propose to classify, by simulation, the shape variability (or non-Gaussianity) of the surface electromyogram (sEMG) amplitude probability density function (PDF), according to contraction level, using high-order statistics (HOS) and a recent functional formalism, the core shape modeling (CSM). According to recent studies, based on simulated and/or experimental conditions, the sEMG PDF shape seems to be modified by many factors as: contraction level, fatigue state, muscle anatomy, used instrumentation, and also motor control parameters. For sensitivity evaluation against these several sources (physiological, instrumental, and neural control) of variability, a large-scale simulation (25 muscle anatomies, ten parameter configurations, three electrode arrangements) is performed, by using a recent sEMG-force model and parallel computing, to classify sEMG data from three contraction levels (20, 50, and 80% MVC). A shape clustering algorithm is then launched using five combinations of HOS parameters, the CSM method and compared to amplitude clustering with classical indicators [average rectified value (ARV) and root mean square (RMS)]. From the results screening, it appears that the CSM method obtains, using Laplacian electrode arrangement, the highest classification scores, after ARV and RMS approaches, and followed by one HOS combination. However, when some critical confounding parameters are changed, these scores decrease. These simulation results demonstrate that the shape screening of the sEMG amplitude PDF is a complex task which needs both efficient shape analysis methods and specific signal recording protocol to be properly used for tracking neural drive and muscle activation strategies with varying force contraction in complement to classical amplitude estimators.

Evaluation of HD-sEMG Probability Density Function deformations in ramp exercise.

The aim of the present study is to propose a subject-specific screening approach of High Density surface EMG (HD-sEMG) Probability Density Function (PDF) shape evolution in experimental conditions following a ramp exercise from 0% to 50% of the Maximum Voluntary Contraction (MVC) during 25 seconds of isometric contractions of the Biceps Brachii from six healthy subjects. This method uses High Order Statistics (HOS), namely the kurtosis and the skewness for PDF shape screening examined on selectively positioned Laplacian sEMG channels obtained on an 8×8 HD-sEMG grid. For each subject, the position of the Laplacian channels was chosen based on the level of muscle activation obtained from the Signal to Noise Ratio (SNR) matrix computed for the 64 sEMG signals of the grid in order to obtain independent Laplacian configurations localized in areas with high SNRs indicating high muscle activation. Afterwards, we used the Principal Component Analysis (PCA) to obtain the principal trend of the kurtosis and the skewness computed from the selected Laplacian signals according to force level variation. The obtained results show a globally common increasing HOS trend according to force increase from 0% to 50% MVC for all the subjects regardless of the anatomical, instrumental and physiological variability that usually strongly influences these trends.

Robust functional statistics applied to Probability Density Function shape screening of sEMG data.

Recent studies pointed out possible shape modifications of the Probability Density Function (PDF) of surface electromyographical (sEMG) data according to several contexts like fatigue and muscle force increase. Following this idea, criteria have been proposed to monitor these shape modifications mainly using High Order Statistics (HOS) parameters like skewness and kurtosis. In experimental conditions, these parameters are confronted with small sample size in the estimation process. This small sample size induces errors in the estimated HOS parameters restraining real-time and precise sEMG PDF shape monitoring. Recently, a functional formalism, the Core Shape Model (CSM), has been used to analyse shape modifications of PDF curves. In this work, taking inspiration from CSM method, robust functional statistics are proposed to emulate both skewness and kurtosis behaviors. These functional statistics combine both kernel density estimation and PDF shape distances to evaluate shape modifications even in presence of small sample size. Then, the proposed statistics are tested, using Monte Carlo simulations, on both normal and Log-normal PDFs that mimic observed sEMG PDF shape behavior during muscle contraction. According to the obtained results, the functional statistics seem to be more robust than HOS parameters to small sample size effect and more accurate in sEMG PDF shape screening applications.

Nonlinear estimation of coupling and directionality between signals: application to uterine EMG propagation.

Understanding the direction and quantity of information flowing in a complex system is a fundamental task in signal processing. Several measures have been proposed to detect the quantity of synchronization and the directionality between time series and in physiological data. In this paper we use two methods that are widely used in synchronization and directionality analysis: Nonlinear correlation coefficient (h(2)) and the general synchronization (H). The performances of both methods were tested on four dimensional coupled synthetic nonlinear Rössler models. They were then applied to a single real labor contraction uterine EMG burst with the aim of using them to detect synchronization and to plot the map of direction of information flow between the whole signal channels. The results on synthetic signal show a slight superiority of H over h(2). The results obtained on a single contraction are encouraging for the future use of these tools for resolving the open question of the directionality of uterine contractions and may provide a way of finding their source loci.

The use of a neural network system in the identification of motor unit characteristics from surface detected action potentials: a simulation study.

The surface detected motor unit action potential (MUAP) morphology depends on many physiological and anatomical characteristics of the contracting muscle that are not directly accessible to measurement. In this paper, a neural network based approach is proposed to estimate the motor unit (MU) parameters from a simulated single surface MUAP. We have developed an estimation system that is composed of the following stages: conduction velocity estimation, signal dimension reduction, MU parameters estimation, and number of MU fibres estimation. The parameter estimation stage employs four multilayer neural networks trained on simulated MUAPs corresponding to various ranges of MU parameters. In the estimation mode, this module produces four MU parameters sets. The selected set of the five muscle characteristics is that which minimises an error criterion on a signal reconstructed from the estimated parameters. The proposed system is tested with several simulated MUAPs signals with additive white noise in order to evaluate its performance. It is shown that the technique performs well when the signal to noise ratio is greater than 20 dB.

Renal hemodynamic and functional effect of PEEP ventilation in human renal transplantations.

Increased intrathoracic pressure with positive pressure breathing (PPB) induces renal hypoperfusion and excretion function impairment the mechanism of which may be partially related to reflex sympathetic nerve activation. The consequences of renal denervation on PPB-induced renal impairment are unknown. This study was conducted to evaluate the effects of increasing intrathoracic pressure with positive end-expiratory pressure (PEEP) on renal blood flow (RBF, pulsed Doppler implantable microprobes) and function in 12 kidney transplantation recipients during the immediate post-transplantation period. Three sets of measurements were performed during successively zero end-expiratory pressure (ZEEP), 15 cm H2O PEEP, and back to ZEEP. PEEP ventilation was associated with mean arterial pressure (MAP) and cardiac output (CO) decrease (-12%, p < 0.01; -26%, p < 0.01, respectively). RBF remained constant in the three protocol conditions. PEEP ventilation was associated with a decrease in urinary output (8.5 +/- 5.6 versus 12.9 +/- 8.6 ml/min; p < 0.01), urinary sodium concentration (115 +/- 14 versus 121 +/- 12 mmol/L; p < 0.01) sodium excretion rate (1 +/- 0.7 versus 1.6 +/- 1.1 mmol/min; p < 0.01), and creatinine clearance (17.1 +/- 10 versus 23.2 +/- 13.6 ml/min; p < 0.01). PEEP-induced urinary output decrease was correlated to renal perfusion pressure decrease (r = 0.7, p = 0.016). These results suggest that despite denervation and renal blood flow stability, renal handling of water and salt is perfusion pressure-dependent during PEEP in human renal allograft recipients.

Decreased mesenteric blood flow supplying retrosternal esophageal ileocoloplastic grafts during positive-pressure breathing.

Esophageal replacement after esophagogastric injury caused by ingestion of lye may require the interposition of a retrosternal ileocolic graft. In this new anatomic situation, the mesenteric circulation supplying the graft is subjected to the intrathoracic pressure surrounding the graft. Thus, mesenteric blood flow supplying the graft may be impaired when intrathoracic pressure is increased during mechanical ventilation. This study was designed to evaluate the effect of increasing intrathoracic pressure by application of a positive end-expiratory pressure on mesenteric blood flow supplying esophageal ileocolic grafts. Eight cases were studied in the immediate postoperative period. Miniaturized implantable Doppler microprobes were sutured to the single artery supplying the graft and connected to an 8 MHz pulsed Doppler flowmeter. Two sets of measurements were successively performed with zero end-expiratory pressure ventilation and after application of a 15 cm water positive end-expiratory pressure. Positive end-expiratory pressure induces mean arterial pressure (-12%); p < 0.05) and cardiac output (-17%; p < 0.05) decrease. Mesenteric blood flow also decreases (-38%; p < 0.05) as did the mesenteric blood flow/cardiac output ratio, suggesting a potential mesenteric vasoconstriction assessed by mesenteric vascular resistance increase and mesenteric diastolic blood flow velocity decrease. These results suggest that, in the particular anatomic situation of the graft, increased intrathoracic pressure induces mesenteric blood flow decrease in relation to systemic hemodynamic alterations associated with perivisceral pressure increase. This change may be deleterious to graft perfusion.

Successful treatment of vasospastic acute ischaemia with intra-arterial nicardipine.

Accidental intra-arterial injection of a colouring agent (Bonney's blue) in a 28-year-old male patient induced acute ischaemia of the lower limb, resistant to standard therapy. Its successful treatment was finally obtained by intra-arterial infusion of nicardipine.

Usefulness of perioperative pulsed Doppler flowmetry in predicting postoperative local ischemic complications after ileocolic esophagoplasty.

Regional ischemia may induce cervical anastomosis leakage or stenosis or graft necrosis after esophageal reconstruction by retrosternal interposition of an ileocolic graft. These complications may be related to systemic or local hemodynamic alterations. This study was designed to evaluate the relationship between immediate postoperative arterial blood supply to the graft, arterial patency monitored by angiography, and clinical outcome. Eight patients (mean age 30 +/- 4 years; standard deviation) were studied. Miniaturized Doppler implantable microprobes were sutured to the single artery supplying the graft and connected to an 8 MHz pulsed Doppler flowmeter. Systemic hemodynamic parameters and mesenteric hemodynamic data were collected 3 hours after the end of the surgical procedure. These data were compared with the angiogram of the right superior colic artery supplying the graft, systematically performed on the fifteenth postoperative day, and with the clinical course of follow-up for 3 months. Five patients (group 1) had excellent clinical and angiographic results. Mean mesenteric blood flow in these patients was 51 +/- 49 ml.min-1 (+/- standard deviation, ranging from 9 to 122). Three patients (group 2) had a poor clinical outcome. One had early complete graft necrosis and the two others had leakage of the cervical anastomosis with poor distal arterial vascularization of the graft on the angiogram. Mean mesenteric blood flow was nul in the first patient and, respectively, 24 and 28 ml.min-1 in the two others. Cardiac output and mean arterial pressure were in the same range for all patients. Phasic velocity shape analysis revealed that the three group 2 patients had an end-systolic or end-diastolic reverse flow pattern that was not observed in the five group 1 patients, which suggested a submaximal increase in downstream vascular resistance. This reverse flow pattern seems to be a good predictor of ischemia-related complications. We conclude that perioperative pulsed Doppler blood flow monitoring in an ileocolic graft may be useful for the diagnosis and prevention of ischemic complications.

Isoflurane, and not halothane, increases mesenteric blood flow supplying esophageal ileocoloplasty.

Regional ischemia may induce anastomotic leakage or stenosis after esophageal reconstruction using retrosternal interposition of an ileocolic graft. These complications may be related to systemic or local hemodynamic alterations. This study was designed to evaluate the influence of inhalational anesthetic agents on the intestinal circulation supplying these ileocolic grafts. Seven patients (age 30 +/- 5 yr, mean +/- standard deviation [SD]) were studied in the immediate postlaparotomy period. Miniaturized Doppler implantable microprobes were sutured to the single artery supplying the graft and connected to an 8-MHz pulsed Doppler flowmeter. Continuous fentanyl infusion (300 micrograms.h-1) was maintained throughout the study. Measurements were performed at the end of four 30-min periods, which were, successively: first control; isoflurane or halothane anesthesia; second control; and isoflurane or halothane anesthesia. Isoflurane and halothane were administered in cross sequence with end-tidal concentration of 0.8% and 0.5%, respectively, to induce equipotent anesthesia. Both anesthetics induced similar decreases in mean systemic arterial pressure (MAP), cardiac output (CO), and systemic vascular resistance. During isoflurane, mean mesenteric blood flow (MBFm) supplying the graft was increased (+38%; P less than 0.05), and the mesenteric vascular resistance index (MVRI; -44%; P less than 0.05) was decreased, leading to an increase in the MBFm/CO ratio (P less than 0.05). Halothane changed neither the MBFm nor the MBFm/CO ratio, despite a mild decrease in MVRI (-14%; P less than 0.05). Diastolic blood flow velocity increased significantly (2.3 +/- 0.9 vs. 0.8 +/- 0.3 cm.s-1, P less than 0.05) only with isoflurane, suggesting a local vasodilation not observed with halothane.(ABSTRACT TRUNCATED AT 250 WORDS)