Propagation of spontaneous electrical activity in the ex vivo human uterus.

Contractions of the non-pregnant uterus play a key role in fertility. Yet, the electrophysiology underlying these contractions is poorly understood. In this paper, we investigate the presence of uterine electrical activity and characterize its propagation in unstimulated ex vivo human uteri. Multichannel electrohysterographic measurements were performed in five freshly resected human uteri starting immediately after hysterectomy. Using an electrode grid externally and an electrode array internally, measurements were performed up to 24 h after hysterectomy and compared with control. Up to 2 h after hysterectomy, we measured biopotentials in all included uteri. The median root mean squared (RMS) values of the external measurements ranged between 3.95 µV (interquartile range (IQR) 2.41-14.18 µV) and 39.4 µV (interquartile range (IQR) 10.84-105.64 µV) and were all significantly higher than control (median RMS of 1.69 µV, IQR 1.13-3.11 µV), consisting of chicken breast meat. The RMS values decreased significantly over time. After 24 h, the median RMS (1.27 µV, IQR 0.86-3.04 µV) was comparable with the control (1.69 µV, IQR 1.13-3.11 µV, p = 0.125). The internal measurements showed a comparable pattern over time, but overall lower amplitude. The measured biopotentials propagated over the uterine surface, following both a plane-wave as well as an erratic pattern. No clear pacemaker location nor a preferred propagation direction could be identified. These results show that ex vivo uteri can spontaneously generate propagating biopotentials and provide novel insight contributing to improving our understanding of the electrophysiology of the human non-pregnant uterus.

Assessment of uterine activity during IVF by quantitative ultrasound imaging: a pilot study.

RESEARCH QUESTION: Does uterine activity differ in patients who have undergone successful IVF treatment compared with patients who have undergone unsuccessful IVF treatment? DESIGN: Prospective study of 16 women who underwent fresh single embryo transfer. All patients underwent transvaginal ultrasound in three phases of the IVF treatment: ovarian stimulation 1 h before embryo transfer (ET1) and 5-7 days after embryo transfer (ET5-7). Uterine motion analysis was implemented by a dedicated speckle tracking algorithm; frequency- and amplitude-related features were extracted from the derived signals to characterize the uterine activity in relation to ongoing implantation (positive HCG after 6 weeks) and ongoing pregnancy at 11 weeks. RESULTS: Uterine activity in terms of frequency (ovarian stimulation ET1, P = 0.04; ovarian stimulation ET5-7, P = 0.002) and amplitude (ovarian stimulation ET1, P = 0.0003; ovarian stimulation ET5-7, P = 0.000008) is significantly higher in the ovarian stimulation phase compared with ET1 and ET5-7. Women with ongoing pregnancies showed significantly higher uterine contraction frequency compared with those with no ongoing pregnancies in all phases (ovarian stimulation, P = 0.006; ET1, P = 0.015; ET5-7, P = 0.007). Uterine contraction amplitude was significantly lower (P = 0.037) in women at ET5-7 in women with ongoing pregnancies. CONCLUSIONS: This study is a first step towards assessing uterine activity during IVF objectively and non-invasively. It is an essential step to understanding the previously suggested effect of contractions on IVF failure. Uterine activity after embryo transfer characterized by high frequency and low amplitude may favour embryo implantation. Research with larger patient cohorts is needed to build on current evidence and knowledge of uterine contractions during IVF.

Comparative Review of the Algorithms for Removal of Electrocardiographic Interference from Trunk Electromyography.

Surface electromyogram (EMG) is a noninvasive measure of muscle electrical activity and has been widely used in a variety of applications. When recorded from the trunk, surface EMG can be contaminated by the cardiac electrical activity, i.e., the electrocardiogram (ECG). ECG may distort the desired EMG signal, complicating the extraction of reliable information from the trunk EMG. Several methods are available for ECG removal from the trunk EMG, but a comparative assessment of the performance of these methods is lacking, limiting the possibility of selecting a suitable method for specific applications. The aim of the present study is therefore to review and compare the performance of different ECG removal methods from the trunk EMG. To this end, a synthetic dataset was generated by combining in vivo EMG signals recorded on the biceps brachii and healthy or dysrhythmia ECG data from the Physionet database with a predefined signal-to-noise ratio. Gating, high-pass filtering, template subtraction, wavelet transform, adaptive filtering, and blind source separation were implemented for ECG removal. A robust measure of Kurtosis, i.e., KR2 and two EMG features, the average rectified value (ARV), and mean frequency (MF), were then calculated from the processed EMG signals and compared with the EMG before mixing. Our results indicate template subtraction to produce the lowest root mean square error in both ARV and MF, providing useful insight for the selection of a suitable ECG removal method.

Uterine peristalsis and fertility: current knowledge and future perspectives: a review and meta-analysis.

Although uterine contractions in the non-pregnant uterus have been studied extensively, the knowledge gained has not been used in general fertility treatment work-up. In this review paper, we provide an overview of the current knowledge on uterine peristalsis (UP), based on the available literature. This literature shows that UP influences pregnancy chances in both natural and artificial cycles. Although the physiological background of these contractions is not completely clear, we know that several factors can be of influence, like uterine pathologies and hormones. Several options to alter pregnancy outcome by interfering with uterine contractions have been studied. Our meta-analysis on therapeutic options shows positive results of progesterone at time of embryo transfer in IVF cycles or prostaglandins at time of intrauterine insemination, although the quality of evidence is low. These therapies are probably most beneficial in selected groups of patients with abnormal contraction patterns. The introduction of an objective and user-friendly UP measuring tool suitable for use in daily practice would make it possible to identify and monitor these patients. We suggest that future research should focus on the physiology of initiation of UP and on the development of an effective standard measuring tool.

Eight-Week Vibration Training of the Elbow Flexors by Force Modulation: Effects on Dynamic and Isometric Strength.

Vibration exercise (VE) has been suggested as an effective method to improve strength and power capabilities. However, the underlying mechanisms in response to VE are still unclear. A pulley-like VE system, characterized by sinusoidal force applications has been developed and tested for proof of concept in a previous study. The aim of this study was to evaluate the effects of such force modulation on elbow flexors strength and compare it with conventional methods. Forty subjects were randomly divided into 4 groups of 10: the vibration group (VG), the no-vibration group (NVG), the dumbbell group (DG), and the control group (CG). Biceps curl exercises were used to train the elbow flexors 2 times a week for 8 weeks. Subjects in the VG were trained using a ramp-up baseline with superimposed 30 Hz sinusoidal vibration whereas the subjects in the NVG were trained using the same baseline but without vibration. Subjects in the DG were trained using dumbbells, and the subjects in the CG were not trained. The isometric break force (IBF) and 1 repetition maximum (1RM) of the subject's dominant arm were assessed before and after the 8-week training period. The VG achieved 1RM improvement (22.7%) larger than the NVG (10.8%) and comparable with the DG (22.3%). Differences in IBF gains following the training period among the training groups were found to be not significant. Our results support the inclusion of the proposed VE in strength training programs aimed at improving dynamic strength on the elbow flexors.

On the nature of the electromyographic signals recorded during vibration exercise.

PURPOSE: Surface electromyography (EMG) has been widely used to measure neuromuscular activity during vibration exercise (VE) to investigate the underlying mechanisms elicited by VE. However, the EMG spectrum recorded during VE shows sharp peaks at the vibration frequency whose interpretation remains controversial. Some authors considered those peaks as a result of motion artifacts, while others interpreted them as due to vibration-induced neuromuscular activity. The aim of the present study is to clarify the nature of those sharp peaks observed during VE. METHODS: Three independent EMG measurements were performed during VE: in vitro (IVT), in vivo at rest ([Formula: see text]), and in vivo during voluntary contraction ([Formula: see text]). The amplitudes of the EMG vibration frequency components ([Formula: see text]) were extracted for all measurements. The conduction velocity (CV) of the vibration frequency components and the full EMG spectrum were also estimated during voluntary contraction. RESULTS: Our spectrum analysis revealed small [Formula: see text] for IVT and [Formula: see text], accounting for only 3.3 and 7.6 % of that obtained from [Formula: see text]. Moreover, the CV estimation indicated the EMG vibration components to propagate along the muscle fiber with CV [Formula: see text] 6.5 m/s, comparable to the CV estimated using the full EMG spectrum (5.7 m/s). CONCLUSION: We may therefore conclude that the sharp spectral peaks observed during VE are mainly due to vibration-induced muscle activity rather than motion artifacts.

Study protocol: PoPE-Prediction of Preterm delivery by Electrohysterography.

BACKGROUND: Traditional methods used for prediction of preterm delivery are subjective and inaccurate. The Electrohysterogram (EHG) and in particular the estimation of the EHG conduction velocity, is a relatively new promising method for detecting imminent preterm delivery. To date the analysis of the conduction velocity has relied on visual inspection of the signals. As a next step towards the introduction of EHG analysis as a clinical tool, we propose an automated method for EHG conduction velocity estimation for both the speed and direction of single spike propagation. METHODS/DESIGN: The study design will be an observational cohort study. 100 pregnant women, gestational age between 23 + 5 and 34 weeks, admitted for threatening preterm labor or preterm prelabor rupture of membranes, will be included. The length of the cervical canal will be measured by transvaginal ultrasound. The EHG will be recorded using 4 electrodes in a fixed configuration. Contractions will be detected by analysis of the EHG and using an estimation of the intra uterine pressure. In the selected contractions, the delays between channels will be estimated by cross-correlation, and subsequently, the average EHG conduction velocity will be derived. Patients will be classified as labor group and non-labor group based on the time between measurement and delivery. The average conduction velocity and cervical length will be compared between the groups. The main study endpoints will be sensitivity, specificity, and area under the ROC curve for delivery within 1,2,4,7, and 14 days from the measurement. DISCUSSION: In this study, the diagnostic accuracy of EHG conduction velocity analysis will be evaluated for detecting preterm labor. Visual and automatic detection of contractions will be compared. Planar wave propagation will be assumed for the calculation of the CV vector. TRIAL REGISTRATION: Current Controlled Trials ISRCTN07603227.

Electrohysterographic evaluation of preterm contractions in a patient with a unicornuate uterus.

Women with Müllerian anomalies are at increased risk of preterm labor. The analysis of parameters derived by the electrohysterogram such as its conduction velocity are promising for preterm delivery prediction. However, an electrohysterogram has never been measured in Müllerian anomalies. A multiparous woman with a unicornuate uterus presented at 28 weeks of gestation with preterm contractions. Three electrohysterogram recordings were performed between 28 and 30 weeks of gestation, 4 weeks before delivery. The conduction velocity values were in line with previous literature and differed significantly (p < 0.001) showing an increase between the first and last two recordings. The parameters derived from the electrohysterogram such as conduction velocity and power density spectrum peak frequency are promising ones to follow the evolution of pregnancy towards labor, and to distinguish between productive and unproductive uterine contractions, in the case of a unicornuate uterus as well as one that is normally developed.

Towards improving uterine electrical activity modeling and electrohysterography: ultrasonic quantification of uterine movements during labor.

The electrohysterogram is a potential new tool for diagnosing preterm labor. Parameters from the electrohysterogram may be influenced by uterine movement. An observational study was performed quantifying uterine movement during labor as a step towards improving electrohysterogram analysis for predicting preterm labor. The uterine wall was continuously tracked by ultrasound imaging during first stage of labor while an accelerometer recorded external abdominal accelerations in six women. A cyclic cranial-caudal movement of the uterine wall, caused by maternal respiration, was observed. This is reported and quantified for the first time. Average frequency, amplitude, and peak speed were 0.27 ± 0.07 Hz, 0.68 ± 0.84 cm, and 1.04 ± 1.20 cm/s, respectively. The accelerometer signal correlated with uterine movement and therefore can possibly provide a reference for removing movement-induced artifacts. There is a need to model and measure the effect of uterine movement on the electrohysterogram parameters and make measurements more robust to movement artifacts.

Automatic Optimization of Multichannel Electrode Configurations for Robust Fetal Heart Rate Detection by Blind Source Separation.

OBJECTIVE: Fetal heart rate (fHR) evaluation is fundamental to guarantee timely medical intervention in case of pregnancy complications. Due to the limitations of traditional cardiotocography, multichannel electrophysiological recording was proposed as a viable alternative, which requires Blind Source Separation (BSS) techniques. Yet effective and reliable separation of the fetal ECG remains challenging due to multiple noise sources and the effects of varying fetal position. In this work, we demonstrate that the adopted electrode configuration plays a key role in the effectiveness of BSS and propose guidelines for optimal electrode positioning. Moreover, a model is proposed to automatically predict the most suited configuration for accurate BSS-based fHR estimation with a minimal number of leads, to facilitate practical implementation. METHODS: We compared fHR estimation accuracy with different electrode configurations on in-silico data, identifying the optimal configuration for a recent BSS method. Based on features extracted from raw signals, we proposed a support vector regression model to automatically identify the best electrode configuration in terms of fHR estimation accuracy and to dynamically adjust it to varying fetal presentation. Evaluation was performed on real and synthetic data. RESULTS: Guidelines for the optimal electrode configuration are proposed by using 4 leads. Prediction of configuration quality shows 80.9% accuracy; the optimal configurat- ion is recognized in 92.2% of the subjects. CONCLUSION: The proposed method successfully predicts the quality of the configurations, demonstrating the impact of the electrode configuration on the BSS performance. SIGNIFICANCE: The method holds potential for long-term fetal monitoring, by dynamically choosing the optimal configuration.

Speckle Tracking Echocardiography in Hypertensive Pregnancy Disorders: A Systematic Review.

IMPORTANCE: Hypertensive pregnancy disorders (HPDs) are associated with an increased risk of long-term cardiovascular disease. Speckle tracking echocardiography (STE) might be useful in the early detection of preclinical cardiac changes in women with HPDs. OBJECTIVE: The aim of this study was to study whether STE is a suitable method to detect differences in cardiac function in pregnant women with HPD compared with normotensive pregnant women or between women with a history of a pregnancy complicated by HPD compared with women with a history of an uncomplicated pregnancy. EVIDENCE ACQUISITION: The databases Medline, EMBASE, and Central were systematically searched for studies comparing cardiac function measured with STE in pregnant women with HPD or women with a history of HPD and women with a history of normotensive pregnancies. RESULTS: The search identified 16 studies, including 870 women with a history of HPD and 693 normotensive controls. Most studies during pregnancy (n = 12/13) found a decreased LV-GLS (left ventricular global longitudinal strain) in HPD compared with normotensive pregnant controls. LV-GRS (left ventricular global radial strain) and LV-GLCS (left ventricular global circumferential strain) are decreased in women with early-onset and severe preeclampsia. Women with a history of early-onset preeclampsia show lasting myocardial changes, with significantly decreased LV-GLS, LV-GLCS, and LV-GRS. CONCLUSIONS AND RELEVANCE: LV-GLS is significantly decreased in pregnant women with HPD compared with normotensive pregnant women. Other deformation values show a significant decrease in women with severe or early-onset preeclampsia, with lasting myocardial changes after early-onset preeclampsia.

Inter-electrode delay estimators for electrohysterographic propagation analysis.

Premature birth is a major cause of mortality and permanent dysfunctions. Several parameters derived from single channel electrohysterographic (EHG) signals have been considered to determine contractions leading to preterm delivery. The results are promising, but improvements are needed. As effective uterine contractions result from a proper action potential propagation, in this paper we focus on the propagation properties of EHG signals, which can be predictive of preterm delivery. Two standard delay estimators, namely maximization of the cross-correlation function and spectral matching, are adapted and implemented for the assessment of inter-electrode delays of propagating EHG signals. The accuracy of the considered standard estimators might be hampered by a poor inter-channel correlation. An improved dedicated approach is therefore proposed. By simultaneous adaptive estimation of the volume conductor transfer function and the delay, a dedicated method is conceived for improving the inter-channel signal similarity during delay calculation. Furthermore, it provides delay estimates without resolution limits and it is suitable for low sampling rates, which are appropriate for EHG recording. The three estimators were evaluated on EHG signals recorded on seven women. The dedicated approach provided more accurate estimates due to a 22% improvement of the initial average inter-channel correlation.

Dedicated Ultrasound Speckle Tracking for Quantitative Analysis of Uterine Motion Outside Pregnancy.

Fertility problems are nowadays being paralleled by important advances in assisted reproductive technologies. Yet the success rate of these technologies remains low. There is evidence that fertilization outcome is affected by uterine motion, but solutions for quantitative analysis of uterine motion are lacking. This work proposes a dedicated method for uterine-motion quantification by B-mode transvaginal ultrasound. Motion analysis is implemented by speckle tracking based on block matching after speckle-size regularization. Sum of absolute differences is the adopted matching metrics. Prior to the analysis, dedicated singular value decomposition (SVD) filtering is implemented to enhance the uterine motion over noise, clutter, and uncorrelated motion induced by neighboring organs and probe movements. SVD and block matching are first optimized by a dedicated ex vivo setup. Robustness to noise and speckle decorrelation is improved by median filtering of the tracking coordinates from surrounding blocks. Speckle tracking is further accelerated by a diamond search. The method feasibility was tested in vivo with a longitudinal study on nine women, aimed at discriminating between four selected phases of the menstrual cycle known to show different uterine behavior. Each woman was scanned in each phase for 4 min; four sites on the uterine fundus were tracked over time to extract strain and distance signals along the longitudinal and transversal directions of the uterus. Several features were extracted from these signals. Among these features, median frequency and contraction frequency showed significant differences between active and quiet phases. These promising results motivate toward an extended validation in the context of fertilization procedures.

Machine learning for classification of uterine activity outside pregnancy.

The objective of this study was to investigate the use of classification methods by a machine-learning approach for discriminating the uterine activity during the four phases of the menstrual cycle. Four different classifiers, including support vector machine (SVM), K-nearest neighbors (KNN), Gaussian mixture model (GMM) and naïve Bayes are here proposed. A set of amplitude- and frequency-features were extracted from signals measured by two different quantitative and noninvasive methods, such as electrohysterography and ultrasound speckle tracking. The proposed classifiers were trained using all possible feature combinations. The method was applied on a database (24 measurements) collected in different phases of the menstrual cycle, comprising uterine active and quiescent phases. The SVM classifier showed the best performance for discrimination between the different menstrual phases. The classification accuracy, sensitivity, and specificity were 90%, 79%, 93%, respectively. Similar methods can in the future contribute to the diagnosis of infertility or other common uterine diseases such as endometriosis.

Estimation of internal uterine pressure by joint amplitude and frequency analysis of electrohysterographic signals.

Monitoring the uterine contraction provides important prognostic information during pregnancy and parturition. The existing methods employed in clinical practice impose a compromise between reliability and invasiveness. A promising technique for uterine contraction monitoring is electrohysterography (EHG). The EHG signal measures the electrical activity which triggers the contraction of the uterine muscle. In this paper, a non-invasive method for intrauterine pressure (IUP) estimation by EHG signal analysis is proposed. The EHG signal is regarded as a non-stationary signal whose frequency and amplitude characteristics are related to the IUP. After acquisition in a multi-channel configuration, the EHG signal is therefore analyzed in the time-frequency domain. A first estimation of the IUP is then derived by calculation of the unnormalized first statistical moment of the frequency spectrum. The estimation accuracy is finally increased by identification of a second-order polynomial model. The proposed method is compared to root mean squared analysis and optimal linear filtering and validated by simultaneous measurement of the IUP on nine women during labor. The results suggest that the proposed EHG signal analysis provides an accurate estimate of the IUP.

Feasibility of Transabdominal Electrohysterography for Analysis of Uterine Activity in Nonpregnant Women.

PURPOSE: Uterine activity plays a key role in reproduction, and altered patterns of uterine contractility have been associated with important physiopathological conditions, such as subfertility, dysmenorrhea, and endometriosis. However, there is currently no method to objectively quantify uterine contractility outside pregnancy without interfering with the spontaneous contraction pattern. Transabdominal electrohysterography has great potential as a clinical tool to characterize noninvasively uterine activity, but results of this technique in nonpregnant women are poorly documented. The purpose of this study is to investigate the feasibility of transabdominal electrohysterography in nonpregnant women. METHODS: Longitudinal measurements were performed on 22 healthy women in 4 representative phases of the menstrual cycle. Twelve electrohysterogram-based indicators previously validated in pregnancy have been estimated and compared in the 4 phases of the cycle. Using the Tukey honest significance test, significant differences were defined for P values below .05. RESULTS: Half of the selected electrohysterogram-based indicators showed significant differences between menses and at least 1 of the other 3 phases, that is the luteal phase. CONCLUSION: Our results suggest transabdominal electrohysterography to be feasible for analysis of uterine activity in nonpregnant women. Due to the lack of a golden standard, this feasibility study is indirectly validated based on physiological observations. However, these promising results motivate further research aiming at evaluating electrohysterography as a method to improve understanding and management of dysfunctions (possibly) related to altered uterine contractility, such as infertility, endometriosis, and dysmenorrhea.

Dedicated Entropy Measures for Early Assessment of Pregnancy Progression From Single-Channel Electrohysterography.

OBJECTIVE: Preterm birth is a large-scale clinical problem involving over 10% of infants. Diagnostic means for timely risk assessment are lacking and the underlying physiological mechanisms unclear. To improve the evaluation of pregnancy before term, we introduce dedicated entropy measures derived from a single-channel electrohysterogram (EHG). METHODS: The estimation of approximate entropy (ApEn) and sample entropy (SampEn) is adjusted to monitor variations in the regularity of single-channel EHG recordings, reflecting myoelectrical changes due to pregnancy progression. In particular, modifications in the tolerance metrics are introduced for improving robustness to EHG amplitude fluctuations. An extensive database of 58 EHG recordings with 4 monopolar channels in women presenting with preterm contractions was manually annotated and used for validation. The methods were tested for their ability to recognize the onset of labor and the risk of preterm birth. Comparison with the best single-channel methods according to the literature was performed. RESULTS: The reference methods were outperformed. SampEn and ApEn produced the best prediction of delivery, although only one channel showed a significant difference () between labor and nonlabor. The modified ApEn produced the best prediction of preterm delivery, showing statistical significance () in three channels. These results were also confirmed by the area under the receiver operating characteristic curve and fivefold cross validation. CONCLUSION: The use of dedicated entropy estimators improves the diagnostic value of EHG analysis earlier in pregnancy. SIGNIFICANCE: Our results suggest that changes in the EHG might manifest early in pregnancy, providing relevant prognostic opportunities for pregnancy monitoring by a practical single-channel solution.

Clinical Use of Electrohysterography During Term Labor: A Systematic Review on Diagnostic Value, Advantages, and Limitations.

IMPORTANCE: Real-time electrohysterography (EHG)-based technologies have recently become available for uterine monitoring during term labor. Therefore, obstetricians need to be familiar with the diagnostic value, advantages, and limitations of using EHG. OBJECTIVE: The aims of this study were to determine the diagnostic value of EHG in comparison to (1) the intrauterine pressure catheter (IUPC), (2) the external tocodynamometer (TOCO), and (3) in case of maternal obesity; (4) to evaluate EHG from users' and patients' perspectives; and (5) to assess whether EHG can predict labor outcome. EVIDENCE ACQUISITION: A systematic review was performed in the MEDLINE, EMBASE, and Cochrane library in October 2017 resulting in 209 eligible records, of which 20 were included. RESULTS: A high sensitivity for contraction detection was achieved by EHG (range, 86.0%-98.0%), which was significantly better than TOCO (range, 46.0%-73.6%). Electrohysterography also enhanced external monitoring in case of maternal obesity. The contraction frequency detected by EHG was on average 0.3 to 0.9 per 10 minutes higher compared with IUPC, which resulted in a positive predictive value of 78.7% to 92.0%. When comparing EHG tocograms with IUPC traces, an underestimation of the amplitude existed despite that patient-specific EHG amplitudes have been mitigated by amplitude normalization. Obstetricians evaluated EHG tocograms as better interpretable and more adequate than TOCO. Finally, potential EHG parameters that could predict a vaginal delivery were a predominant fundal direction and a lower peak frequency. CONCLUSIONS AND RELEVANCE: Electrohysterography enhances external uterine monitoring of both nonobese and obese women. Obstetricians consider EHG as better interpretable; however, they need to be aware of the higher contraction frequency detected by EHG and of the amplitude mismatch with intrauterine pressure measurements.

Does vibration superimposed on low-level isometric contraction alter motor unit recruitment strategy?

OBJECTIVE: Beneficial effects, including improved muscle strength and power performance, have been observed during vibration exercise (VE) and partially ascribed to a specific reflex mechanism referred to as Tonic vibration reflex (TVR). TVR involves motor unit (MU) activation synchronized and un-synchronized with the vibration cycle; this suggests VE to alter the temporal MU recruitment strategy. However, the effects of VE on MU recruitment remain poorly understood. This study aims to elucidate the influence of VE on MU recruitment indirectly, by investigating the effects of low-intensity VE on muscle activation. APPROACH: Twenty volunteers performed isometric contractions on the biceps brachii of the right arm at a baseline (low) force equal to 30% of the maximum voluntary contraction without vibration (control) and with vibration at 20, 30, 40, and 55 Hz. Three vibration amplitudes were employed at 12.5%, 25%, and 50% of the baseline. Mean muscle-fiber conduction velocity (mCV), mean frequency (MF), and root mean square (RMS) value were estimated from surface electromyography as indicators of the alteration in MU recruitment strategies. MAIN RESULTS: The mCV estimates during VE were significantly (p < 0.05) higher compared to the control condition. Furthermore, six VE conditions produced significantly larger RMS values compared to control condition. The estimated MF did not show any consistent trend. SIGNIFICANCE: These results suggest that vibration superimposed on low-level isometric contraction alters the MU recruitment strategy, activating larger and faster MUs.

A robust fetal ECG detection method for abdominal recordings.

In this paper, we propose a new method for FECG detection in abdominal recordings. The method consists of a sequential analysis approach, in which the a priori information about the interference signals is used for the detection of the FECG. Our method is evaluated on a set of 20 abdominal recordings from pregnant women with different gestational ages. Its performance in terms of fetal heart rate (FHR) detection success is compared with that of independent component analysis (ICA). The results show that our sequential estimation method outperforms ICA with a FHR detection rate of 85% versus 60% of ICA. The superior performance of our method is especially evident in recordings with a low signal-to-noise ratio (SNR). This indicates that our method is more robust than ICA for FECG detection.