Evaluation of Swallowing Related Muscle Activity by Means of Concentric Ring Electrodes.

Surface electromyography (sEMG) can be helpful for evaluating swallowing related muscle activity. Conventional recordings with disc electrodes suffer from significant crosstalk from adjacent muscles and electrode-to-muscle fiber orientation problems, while concentric ring electrodes (CREs) offer enhanced spatial selectivity and axial isotropy. The aim of this work was to evaluate CRE performance in sEMG recordings of the swallowing muscles. Bipolar recordings were taken from 21 healthy young volunteers when swallowing saliva, water and yogurt, first with a conventional disc and then with a CRE. The signals were characterized by the root-mean-square amplitude, signal-to-noise ratio, myopulse, zero-crossings, median frequency, bandwidth and bilateral muscle cross-correlations. The results showed that CREs have advantages in the sEMG analysis of swallowing muscles, including enhanced spatial selectivity and the associated reduction in crosstalk, the ability to pick up a wider range of EMG frequency components and easier electrode placement thanks to its radial symmetry. However, technical changes are recommended in the future to ensure that the lower CRE signal amplitude does not significantly affect its quality. CREs show great potential for improving the clinical monitoring and evaluation of swallowing muscle activity. Future work on pathological subjects will assess the possible advantages of CREs in dysphagia monitoring and diagnosis.

Electrohysterogram for ANN-Based Prediction of Imminent Labor in Women with Threatened Preterm Labor Undergoing Tocolytic Therapy.

Threatened preterm labor (TPL) is the most common cause of hospitalization in the second half of pregnancy and entails high costs for health systems. Currently, no reliable labor proximity prediction techniques are available for clinical use. Regular checks by uterine electrohysterogram (EHG) for predicting preterm labor have been widely studied. The aim of the present study was to assess the feasibility of predicting labor with a 7- and 14-day time horizon in TPL women, who may be under tocolytic treatment, using EHG and/or obstetric data. Based on 140 EHG recordings, artificial neural networks were used to develop prediction models. Non-linear EHG parameters were found to be more reliable than linear for differentiating labor in under and over 7/14 days. Using EHG and obstetric data, the <7- and <14-day labor prediction models achieved an AUC in the test group of 87.1 ± 4.3% and 76.2 ± 5.8%, respectively. These results suggest that EHG can be reliable for predicting imminent labor in TPL women, regardless of the tocolytic therapy stage. This paves the way for the development of diagnostic tools to help obstetricians make better decisions on treatments, hospital stays and admitting TPL women, and can therefore reduce costs and improve maternal and fetal wellbeing.

Electrohysterography in the diagnosis of preterm birth: a review.

Preterm birth (PTB) is one of the most common and serious complications in pregnancy. About 15 million preterm neonates are born every year, with ratios of 10-15% of total births. In industrialized countries, preterm delivery is responsible for 70% of mortality and 75% of morbidity in the neonatal period. Diagnostic means for its timely risk assessment are lacking and the underlying physiological mechanisms are unclear. Surface recording of the uterine myoelectrical activity (electrohysterogram, EHG) has emerged as a better uterine dynamics monitoring technique than traditional surface pressure recordings and provides information on the condition of uterine muscle in different obstetrical scenarios with emphasis on predicting preterm deliveries. OBJECTIVE: A comprehensive review of the literature was performed on studies related to the use of the electrohysterogram in the PTB context. APPROACH: This review presents and discusses the results according to the different types of parameter (temporal and spectral, non-linear and bivariate) used for EHG characterization. MAIN RESULTS: Electrohysterogram analysis reveals that the uterine electrophysiological changes that precede spontaneous preterm labor are associated with contractions of more intensity, higher frequency content, faster and more organized propagated activity and stronger coupling of different uterine areas. Temporal, spectral, non-linear and bivariate EHG analyses therefore provide useful and complementary information. Classificatory techniques of different types and varying complexity have been developed to diagnose PTB. The information derived from these different types of EHG parameters, either individually or in combination, is able to provide more accurate predictions of PTB than current clinical methods. However, in order to extend EHG to clinical applications, the recording set-up should be simplified, be less intrusive and more robust-and signal analysis should be automated without requiring much supervision and yield physiologically interpretable results. SIGNIFICANCE: This review provides a general background to PTB and describes how EHG can be used to better understand its underlying physiological mechanisms and improve its prediction. The findings will help future research workers to decide the most appropriate EHG features to be used in their analyses and facilitate future clinical EHG applications in order to improve PTB prediction.

Identifying physical activity type in manual wheelchair users with spinal cord injury by means of accelerometers.

STUDY DESIGN: This was a cross-sectional study. OBJECTIVES: The main objective of this study was to develop and test classification algorithms based on machine learning using accelerometers to identify the activity type performed by manual wheelchair users with spinal cord injury (SCI). SETTING: The study was conducted in the Physical Therapy department and the Physical Education and Sports department of the University of Valencia. METHODS: A total of 20 volunteers were asked to perform 10 physical activities, lying down, body transfers, moving items, mopping, working on a computer, watching TV, arm-ergometer exercises, passive propulsion, slow propulsion and fast propulsion, while fitted with four accelerometers placed on both wrists, chest and waist. The activities were grouped into five categories: sedentary, locomotion, housework, body transfers and moderate physical activity. Different machine learning algorithms were used to develop individual and group activity classifiers from the acceleration data for different combinations of number and position of the accelerometers. RESULTS: We found that although the accuracy of the classifiers for individual activities was moderate (55-72%), with higher values for a greater number of accelerometers, grouped activities were correctly classified in a high percentage of cases (83.2-93.6%). CONCLUSIONS: With only two accelerometers and the quadratic discriminant analysis algorithm we achieved a reasonably accurate group activity recognition system (>90%). Such a system with the minimum of intervention would be a valuable tool for studying physical activity in individuals with SCI.

Non-invasive electrohysterogram recording using flexible concentric ring electrode.

Non-invasive electrohysterogram (EHG) recording could provide valuable information about uterine dynamics. Bipolar EHG has usually been performed using monopolar disposable electrodes. Recently concentric ring electrodes have been used for EHG recordings so as to acquire more localized electrical activity which may be helpful for deducing uterine contraction efficiency. Nevertheless concentric ring electrodes have commonly been implemented in rigid substrates. Therefore they do not adapt to the body surface curvature which may cause discomfort for patients and a poor contact between electrode and skin. The aim of this paper is to examine the feasibility of picking up EHG signals (BC-EHG) using a new flexible tripolar concentric ring (TCR) electrode placed on the abdominal surface, and to compare it with the conventional bipolar recordings. For this purpose, a total of 7 recording sessions were carried out in 7 pregnant women. Each recording implied simultaneous acquisition of one bipolar EHG signal and of two bipolar concentric EHG (BC-EHG) signals using the flexible TCR electrode. Then a set of temporal and spectral parameters was computed from both bipolar EHG and BC-EHG bursts. Experimental results show no noticeable difference in duration and in dominant frequency in Fast Wave High frequency range. Nonetheless, the low frequency content (0.1-0.2 Hz) of BC-EHG records is smaller than that of bipolar record. These results suggest that the new flexible TCR electrode permits to pick up uterine electrical activity and may provide additional information for deducing uterine efficiency.

Enhancement of non-invasive recording of electroenterogram by means of a flexible array of concentric ring electrodes.

Monitoring intestinal myoelectrical activity by electroenterogram (EEnG) would be of great clinical interest for diagnosing gastrointestinal pathologies and disorders. However, surface EEnG recordings are of very low amplitude and can be severely affected by baseline drifts and respiratory and electrocardiographic (ECG) interference. In this work, a flexible array of concentric ring electrodes was developed and tested to determine whether it can provide surface EEnG signals of better quality than bipolar recordings from conventional disc electrodes. With this aim, sixteen healthy subjects in a fasting state (>8 h) underwent recording. The capability of detecting intestinal pacemaker activity (slow wave) and the influence of physiological interferences were studied. The signals obtained from the concentric ring electrodes proved to be more robust to ECG and respiratory interference than those from conventional disc electrodes. The results also show that intestinal EEnG components such as the slow wave can be more easily identified by the proposed system based on a flexible array of concentric ring electrodes. The developed active electrode array could be a very valuable tool for non-invasive diagnosis of disease states such as ischemia and motility disorders of the small bowel which are known to alter the normal enteric slow wave activity.

Identification of intestinal pacemaker frequency through time-frequency ridge analysis of surface EEnG.

The non-invasive monitoring of the frequency of intestinal pacemaker activity (slow wave, SW) has an important diagnostic value. However the presence of noise, physiological interferences and spurious peaks of the spectral estimators can yield to misidentification of SW frequency when using conventional dominant frequency detection method. In this paper, two methods of ridge extraction from the time-frequency distribution of human surface electroenterogram (EEnG) are proposed for the identification and tracking of SW frequency in 13 recording sessions of 120 minutes in 13 healthy volunteers. The minimum average distance method, that includes of information of previous and subsequent windows of analysis, yields the best results in terms of providing ridges that are longer, with less interruptions and with more stable frequency values which better suit the ubiquity and rhythmicity characteristics of the intestinal SW. This technique permits to reduce misinterpretations of intestinal SW frequency which can be of great importance in diagnostic applications of EEnG.

Prediction of labor using non-invasive Laplacian EHG recordings.

Non-invasive electrohysterogram (EHG) recordings could be used as an alternative technique for monitoring uterine dynamics. Bipolar recordings of EHG have proven to provide valuable information to predict labor. Recently it has been stated that uterine EHG bursts could also be identified in Laplacian recordings on abdominal surface. Taking into account that Laplacian potential technique permits to acquire more localized electrical activity than conventional recordings; these recordings could also be helpful for deducing uterine contraction efficiency. The aim of this paper is to examine the feasibility of Laplacian potential EHG recording for labor prediction and to compare it with monopolar recordings. To this purpose, a total of 42 EHG recordings were acquired from women of similar gestational age: 29 antepartum patients, and 13 patients in labor. Then linear and non-linear classifiers have been implemented using EHG burst parameters as input features. Experimental results show significant differences in temporal and spectral parameters in both monopolar and Laplacian potential recordings between the two groups. In addition, support vector machine based classifier achieved an accuracy of 93% for labor prediction for monopolar recordings, 92% for bipolar recordings and 91% for Laplacian potential.

Comparison of non-invasive electrohysterographic recording techniques for monitoring uterine dynamics.

Non-invasive recording of uterine myoelectric activity (electrohysterogram, EHG) could provide an alternative to monitoring uterine dynamics by systems based on tocodynamometers (TOCO). Laplacian recording of bioelectric signals has been shown to give better spatial resolution and less interference than mono- and bipolar surface recordings. The aim of this work was to study the signal quality obtained from monopolar, bipolar and Laplacian techniques in EHG recordings, as well as to assess their ability to detect uterine contractions. Twenty-two recording sessions were carried out on singleton pregnant women during the active phase of labour. In each session the following simultaneous recordings were obtained: internal uterine pressure (IUP), external tension of abdominal wall (TOCO) and EHG signals (5 monopolar and 4 bipolar recordings, 1 discrete approximation to the Laplacian of the potential and 2 estimates of the Laplacian from two active annular electrodes). The results obtained show that EHG is able to detect a higher number of uterine contractions than TOCO. Laplacian recordings give improved signal quality over monopolar and bipolar techniques, reduce maternal cardiac interference and improve the signal-to-noise ratio. The optimal position for recording EHG was found to be the uterine median axis and the lower centre-right umbilical zone.

Combined method for fetal electrocardiogram extraction from noninvasive abdominal recordings.

Abdominal electrocardiogram (AECG) recording is a non-invasive method to assess fetal well-being during both pregnancy and delivery. However, AECG recording is contaminated by a series of physiological interferences which make difficult the extraction of morphological and temporal parameters of fetal ECG from the raw signals. In this work, it is proposed a combined method to extract the fetal ECG from AECG recording by removing the interferences on a cascade structure using a priori information about the signals nature. In this work, a total of 54 multichannel AECG recordings taken from 21 to 40 weeks of gestation were enrolled. Experimental results show that the proposed method outperforms conventional independent component analysis, and provides fetal heart rate detection in 80% of the cases. In addition it also permits to obtain fetal ECG morphology from AECG recordings.

Recording of electrohysterogram laplacian potential.

Preterm birth is the main cause of the neonatal morbidity. Noninvasive recording of uterine myoelectrical activity (electrohysterogram, EHG) could be an alternative to the monitoring of uterine dynamics which are currently based on tocodynamometers (TOCO). The analysis of uterine electromyogram characteristics could help the early diagnosis of preterm birth. Laplacian recordings of other bioelectrical signals have proved to enhance spatial selectivity and to reduce interferences in comparison to monopolar and bipolar surface recordings. The main objective of this paper is to check the feasibility of the noninvasive recording of uterine myoelectrical activity by means of laplacian techniques. Four bipolar EHG signals, discrete laplacian obtained from five monopolar electrodes and the signals picked up by two active concentric-ringed-electrodes were recorded on 5 women with spontaneous or induced labor. Intrauterine pressure (IUP) and TOCO were also simultaneously recorded. To evaluate the uterine contraction detectability of the different noninvasive methods in comparison to IUP the contractions consistency index (CCI) was calculated. Results show that TOCO is less consistent (83%) than most EHG bipolar recording channels (91%, 83%, 87%, and 76%) to detect the uterine contractions identified in IUP. Moreover laplacian EHG signals picked up by ringed-electrodes proved to be as consistent (91%) as the best bipolar recordings in addition to significantly reduce ECG interference.

Classifier of intestinal contractile activity degree based on internal electroenterogram recording.

The study of the intestinal interdigestive motor migratory complex (IMMC) is relevant in gastroenterology because most of the gastrointestinal pathologies are reflected in anomalies of the IMMC. The aim of this work is to develop an automatic classifier to discriminate among the different intestinal contractile activity degrees (quiescence, irregular, and maximum contractile activity) that compound the IMMC from the internal recordings of electroenterogram. Spectral and statistical parameters estimated from the internal electroenterogram have been used as features to the classifiers based on Linear Discriminant Analysis (LDA) and linear Support Vector Machines (SVM). The accuracy obtained by the SVM classifier is slightly higher than that of the LDA classifier. An accuracy of around 91% was obtained for the binary SVM classifier (quiescence vs maximum activity) and around 74% for the multiclass one. The use of additional features, and non-linear SVM classifiers could yield better classification accuracy values. Nevertheless, preliminary results suggest that SVM classifiers could be a very helpful tool for automatic classification of intestinal contractile activity degrees and for the identification of the IMMC which could be used for diagnosing anomalies in the intestinal motor function.

Enhancement of laplacian EEnG from humans by means of an EMD-based method.

Non-invasive recordings of intestinal myoelectrical activity (Electroenterogram, EEnG) are affected by very-low-frequency (VLF) interferences, respiration, ECG and movement artifacts. In order to identify the intestinal pacemaker activity (slow wave), VLF interferences and respiration should be removed from abdominal surface recordings. In this paper a method based on empirical mode decomposition is proposed to identify and cancel such interferences and to enhance external recordings of human EEnG. The study was carried out on 10 recording sessions in which it was acquired 3 surface EEnG signals by means of active laplacian electrodes, together with respiratory and ECG signals. The application of the proposed method permits to increase the signal-to-interference ratio of EEnG signals from - 7.9 ± 3.3 dB to 6.1 ± 2.7 dB. In addition, the method helps to identify the intestinal pacemaker activity from surface EEnG recordings: the dominant frequency of processed signals is 8.6 ± 1.7 cpm which fits the frequency of the intestinal slow wave in the jejunum, whereas the dominant frequency of original signals was 1.6 ± 1.1 cpm which is associated to VLF interferences.

Combined method for reduction of high frequency interferences in surface electroenterogram (EEnG).

Surface electroenterogram (EEnG) recording is a novel technique for monitoring intestinal motility non-invasively. However, surface EEnG recordings are contaminated by cardiac activity, the respiratory artefact, movement artefacts and other types of interference. The goal of this work is to remove electrocardiogram (ECG) interference and movement artefacts from surface EEnG by means of a combined method of empirical mode decomposition and independent component analysis. For this purpose, 11 recording sessions were conducted on animal models. In order to quantify the effectiveness of the proposed method, several parameters were calculated from each session: signal-to-ECG interference ratio (S/I), energy over 2 Hz (EF2) which quantifies the intestinal motility index of external EEnG recording and the variation of EF2. The proposed method removes both ECG interference and movement artefacts from surface EEnG, obtaining a significantly higher S/I ratio and considerably reducing the non-physiological variation of EF2. Furthermore, after applying the combined method, the correlation coefficient between internal recording EF2 and surface recording EF2 rises significantly. The proposed method could therefore be a useful tool to reduce high frequency interference in EEnG recording and to provide more robust non-invasive intestinal motility indexes.

The detection of intestinal spike activity on surface electroenterograms.

Myoelectrical recording could provide an alternative technique for assessing intestinal motility, which is a topic of great interest in gastroenterology since many gastrointestinal disorders are associated with intestinal dysmotility. The pacemaker activity (slow wave, SW) of the electroenterogram (EEnG) has been detected in abdominal surface recordings, although the activity related to bowel contractions (spike bursts, SB) has to date only been detected in experimental models with artificially favored electrical conductivity. The aim of the present work was to assess the possibility of detecting SB activity in abdominal surface recordings under physiological conditions. For this purpose, 11 recording sessions of simultaneous internal and external myolectrical signals were conducted on conscious dogs. Signal analysis was carried out in the spectral domain. The results show that in periods of intestinal contractile activity, high-frequency components of EEnG signals can be detected on the abdominal surface in addition to SW activity. The energy between 2 and 20 Hz of the surface myoelectrical recording presented good correlation with the internal intestinal motility index (0.64 +/- 0.10 for channel 1 and 0.57 +/- 0.11 for channel 2). This suggests that SB activity can also be detected in canine surface EEnG recording.

Characterization of the sensitivity of a TCB laplacian sensor for surface EEnG recordings.

The improvement of the quality of electroenterogram (EEnG) recordings on abdominal surface could lead to a non-invasive technique to diagnose intestinal motility dysfunctions. In this context, the use of coaxial active electrodes, which permit to record the laplacian potential, can help to achieve such signal enhancement. In this paper, we present a methodology to obtain the maps of sensitivity of this kind of electrodes to pick up the activity of electric dipoles of different orientations. The proposed methodology employs mathematical models, as well as experimental studies (phantoms) to check the theoretical results. The mathematical model of the electrode, and of the human abdomen is developed by means of ANSYS. A simplified physical model is formed by real ring electrodes, a methacrylate tank of size 50 x 50 x 50 cm filled with a saltwater mixture of 2.5 g/l concentration, and moving electric dipoles made by wires of 0.3 mm in diameter. Sensitivity of the sensor is obtained for different depths and different axial distances of vertical and horizontal dipoles. Preliminary results of tripolar ring electrodes in bipolar configuration (TCB) are shown. The obtained results prove the agreement between mathematical and experimental results. The validated model will allow us to study the behavior of laplacian ring electrodes of different dimensions and materials to record the EEnG activity and to analyze the influence of the abdominal layers.

Enhancement of the non-invasive electroenterogram to identify intestinal pacemaker activity.

Surface recording of electroenterogram (EEnG) is a non-invasive method for monitoring intestinal myoelectrical activity. However, surface EEnG is seriously affected by a variety of interferences: cardiac activity, respiration, very low frequency components and movement artefacts. The aim of this study is to eliminate respiratory interference and very low frequency components from external EEnG recording by means of empirical mode decomposition (EMD), so as to obtain more robust indicators of intestinal pacemaker activity from the external EEnG signal. For this purpose, 11 recording sessions were performed in an animal model under fasting conditions and in each individual session the myoelectrical signal was recorded simultaneously in the intestinal serosa and the external abdominal surface in physiological states. Various parameters have been proposed for evaluating the efficacy of the method in reducing interferences: the signal-to-interference ratio (S/I ratio), attenuation of the target and interference signals, the normal slow wave percentage and the stability of the dominant frequency (DF) of the signal. The results show that the S/I ratio of the processed signals is significantly greater than the original values (9.66 +/- 4.44 dB versus 1.23 +/- 5.13 dB), while the target signal was barely attenuated (-0.63 +/- 1.02 dB). The application of the EMD method also increased the percentage of the normal slow wave to 100% in each individual session and enabled the stability of the DF of the external signal to be increased considerably. Furthermore, the variation coefficient of the DF derived from the external processed signals is comparable to the coefficient obtained using internal recordings. Therefore, the EMD method could be a very useful tool to improve the quality of external EEnG recording in the low frequency range and therefore to obtain more robust indicators of the intestinal pacemaker activity from non-invasive EEnG recordings.

Quantification of combined method for interferences reduction in multichannel surface electroenterogram.

Surface electroenterogram (EEnG) is a non-invasive method for monitoring the intestinal motility. However, surface EEnG signals are contaminated by strong physiological interferences. The main interferences which affect high-frequency components of surface EEnG are cardiac activity and movement artifacts. The aim of this work is to quantify the effectiveness of a combined method based on empirical mode decomposition and independent component analysis to remove these interferences from multichannel surface EEnG. In order to do so, several parameters were calculated from five recording sessions: Signal-to-ECG interference ratio (S/I) and variation of energy over 2 Hz (EF2). The results show that the S/I of processed signals was significantly higher than that of original signals, moreover the improvement of the S/I ratio is due to the attenuation of energy associated to interference. The proposed method also allows cancelling movement artifacts from surface EEnG, reducing considerably the non-physiological variation of EF2. Furthermore after the application of the combined method, correlation coefficient between EF2 of internal recording with EF2 of surface recording is greatly higher. Therefore, the proposed method could be helpful to reduce high-frequency interferences in EEnG recording and to provide more robust non-invasive intestinal motility indicators.

Combined method for artifact reduction in surface electroenterogram.

Surface electroenterogram (EEnG) is a non-invasive method for monitoring the intestinal motility. However, surface EEnG recordings are contaminated by movement artifact, cardiac activity, respiratory artifact and other interferences. The aim of this work is to remove movement artifacts by means of a combined method of empirical mode decomposition (EMD) and independent component analysis (ICA). Four recording sessions were conducted on canine model. Surface signals from 4 different channels are decomposed using EMD. Resulting intrinsic mode functions are the inputs of ICA analysis which permits to separate and identify the activities of different origin. Signal components associated to movement artifacts are removed and the original signals are reconstructed by means of an inverse procedure. The results show that the proposed method allows extracting and cancelling movement artifacts from surface EEnG, avoiding the presence of irregular peaks in external intestinal motility indexes. Therefore, the proposed method could be useful to reduce artifacts in EEnG recording and to provide more robust non-invasive intestinal motility indicators.

Empirical mode decomposition: a method to reduce low frequency interferences from surface electroenterogram.

The surface electroenterogram (EEnG) is a non-invasive method of studying myoelectrical bowel activity. However, surface EEnG recordings are contaminated by cardiac activity, respiratory and motion artifacts, and other sources of interference. The aim of this work is to remove the respiration artifact and the very low frequency components from surface EEnG by means of empirical mode decomposition (EMD). Eleven recording sessions were carried out on canine model. Several parameters were calculated before and after the application of the method: signal-to-interference ratio (S/I ratio) and the attenuation level of the signal and of interference. The results show that the S/I ratio was significantly higher after the application of the method (3.68+/-5.54 dB vs. 10.45+/-3.65 dB), the attenuation level of signal and of interference is -0.49+/-0.80 dB versus -7.26+/-5.42 dB, respectively. Therefore, EMD could be a useful aid in identifying the intestinal slow wave and in removing interferences from EEnG recordings.