Fetal ECG Extraction from Abdominal Signals: A Review on Suppression of Fundamental Power Line Interference Component and Its Harmonics
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paper_title: STAN, a clinical audit: the outcome of 2 years of regular use in the city of Varberg, Sweden

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OBJECTIVE ::: To monitor and analyze (audit) the introduction of the STAN methodology in a district hospital. ::: ::: ::: DESIGN ::: Retrospective study covering the total population of deliveries at term during 2004 and 2005. ::: ::: ::: MATERIAL AND METHODS ::: 1,875 out of 3,193 term pregnancies (59%) were monitored using the STAN fetal heart monitor (Neoventa Medical, Moelndal, Sweden) and the associated clinical guidelines. Cord metabolic acidosis, neonatal outcome, and rates of operative deliveries for fetal distress were recorded. ::: ::: ::: RESULTS ::: The overall cesarean section rate was significantly reduced in the STAN group. Emergency (crash) cesarean sections were significantly reduced from 1.51% to 0.27% in the cardiotocography- and STAN-monitored groups, respectively (OR 0.18, 95% CI 0.07-0.49). When cesarean section was performed only because of non-reassuring cardiotocography, cord acid base was significantly higher, 7.26 versus 7.19 (p<0.01), as compared to when STAN guidelines were followed. Total population rates for operative deliveries for fetal distress and cesarean section rates were 6.7% and 3.5% respectively. The corresponding metabolic acidosis rate was 0.5%. ::: ::: ::: CONCLUSION ::: High STAN usage in a busy labor ward setting provided an outcome equaling that noted previously in a larger academic unit, demonstrating the safe implementation of the STAN methodology in a nonacademic unit.
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paper_title: ST-segment analysis of the fetal electrocardiogram improves fetal heart rate tracing interpretation and clinical decision making.

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INTRODUCTION ::: Since its introduction into clinical use, the efficacy of electronic fetal heart rate (FHR) monitoring (EFM) has been questionable. This has been due partly to the marked variation in interpretation of the FHR pattern and subsequent decisions for obstetric intervention, (e.g., the need for prompt delivery). Current application of EFM is limited to the assessment of FHR patterns and uterine contractions. Recent development of higher-order FHR analysis has yielded monitoring systems that can add automated fetal electrocardiographic ST segment analysis to the standard FHR and uterine contraction information. Our goal was to evaluate the effect of adding ST segment analysis to standard FHR information on observer agreement for clinical decision making. ::: ::: ::: METHODS ::: Seven practitioners who were trained and experienced in combined FHR and ST monitoring reviewed 51 fetal monitor tracings, ranging from 2 to 4 h in length. Reviews were conducted in two sessions and at different times. The first session presented only the FHR and uterine contraction information, following which the participants determined the time at which intervention (decision for operative vaginal or Cesarean section delivery) was indicated. In the second session, the participants were provided with a randomized sequence of the same tracings with the addition of ST segment information, as produced by the STAN monitor system (Neoventa Medical, Gothenburg, Sweden). Observer agreement was based on the proportion of participants who agreed on the need for an intervention, and the per cent agreement on the timing of the intervention within 20 min before or after the median time of intervention. ::: ::: ::: RESULTS ::: Of the 51 cases included in this study there were ten fetuses with umbilical artery (UA) pH between 7.05 and 7.14, and nine with UA pH of < 7.05. Observer agreement increased significantly for required intervention when the ST segment information was available for tracing analysis as compared with review of the standard tracing alone (0.96 vs. 0.80, p < 0.05) and the timing of intervention (0.92 vs. 0.66, respectively, p < 0.05). Similarly, correct identification for needed interventions on fetuses with abnormal outcomes increased from 86 to 93% while unneeded interventions on normal fetuses decreased from 43 to 6%. ::: ::: ::: CONCLUSION ::: The addition of ST analysis to standard FHR monitoring improves observer consistency in both the decision for and timing of obstetric interventions. The incorporation of ST segment data with the standard FHR tracing may reduce the number of unneeded obstetric interventions when fetal compromise is absent.
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paper_title: Suppressing harmonic powerline interference using multiple-notch filtering methods with improved transient behavior

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Abstract In signal processing it is often required to have multiple-notch filters which simultaneously possess a very selective magnitude response and a transient response of short duration. Multiple-notch filters are usually used to remove the powerline hum and its harmonics. It is known, that sharper notches are obtained by either using more coefficients in FIR filters, or by placing the pole closer to the unit circle in IIR filters. However, increasing the filter selectivity also increases the duration of the transient process in the filter after the action of the excitation. This paper presents and compares two methods for suppressing the transient response in multiple-notch filters. As an example, these methods have been used to eliminate the powerline noise from the ECG signal. Both filtering techniques are characterized by improved transient behavior compared to the traditional multiple-notch filters. In the first part of the paper a concept of digital IIR multiple-notch filters whose pole radius changes with time is proposed. Owing to a temporary change in the value of the pole radius, the transient can be considerably reduced. In the second part of this review the technique which uses the vector projection to find better initial values for time-invariant multiple-notch filter is presented. Simulations verifying the effectiveness of the proposed IIR multiple-notch filter with time-varying pole radius and the filter with non-zero initial conditions are presented and compared to the performance of the traditional time-invariant filter using an ECG signal with unwanted fixed-frequency harmonic interferences as a study case.
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paper_title: Fetal electrocardiogram (ECG) for fetal monitoring during labour

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BACKGROUND ::: Hypoxaemia during labour can alter the shape of the fetal electrocardiogram (ECG) waveform, notably the relation of the PR to RR intervals, and elevation or depression of the ST segment. Technical systems have therefore been developed to monitor the fetal ECG during labour as an adjunct to continuous electronic fetal heart rate monitoring with the aim of improving fetal outcome and minimising unnecessary obstetric interference. ::: ::: ::: OBJECTIVES ::: To compare the effects of analysis of fetal ECG waveforms during labour with alternative methods of fetal monitoring. ::: ::: ::: SEARCH METHODS ::: The Cochrane Pregnancy and Childbirth Group's Trials Register (latest search 12 February 2013). ::: ::: ::: SELECTION CRITERIA ::: Randomised trials comparing fetal ECG waveform analysis with alternative methods of fetal monitoring during labour. ::: ::: ::: DATA COLLECTION AND ANALYSIS ::: Trial quality assessment and data extraction were performed by one review author, without blinding. ::: ::: ::: MAIN RESULTS ::: Six trials (16,295 women) were included: five trials of ST waveform analysis (15,338 women) and one trial of PR interval analysis (957 women). In comparison to continuous electronic fetal heart rate monitoring alone, the use of adjunctive ST waveform analysis made no significant difference to primary outcomes: births by caesarean section (risk ratio (RR) 0.99, 95% confidence interval (CI) 0.91 to 1.08), the number of babies with severe metabolic acidosis at birth (cord arterial pH less than 7.05 and base deficit greater than 12 mmol/L) (RR 0.78, 95% CI 0.44 to 1.37, data from 14,574 babies), or babies with neonatal encephalopathy (RR 0.54, 95% CI 0.24 to 1.25). There were, however, on average fewer fetal scalp samples taken during labour (RR 0.61, 95% CI 0.41 to 0.91) although the findings were heterogeneous; there were fewer operative vaginal deliveries (RR 0.89, 95% CI 0.81 to 0.98) and admissions to special care unit (RR 0.89, 95% CI 0.81 to 0.99); there was no statistically significant difference in the number of babies with low Apgar scores at five minutes or babies requiring neonatal intubation. There was little evidence that monitoring by PR interval analysis conveyed any benefit. ::: ::: ::: AUTHORS' CONCLUSIONS ::: These findings provide some modest support for the use of fetal ST waveform analysis when a decision has been made to undertake continuous electronic fetal heart rate monitoring during labour. However, the advantages need to be considered along with the disadvantages of needing to use an internal scalp electrode, after membrane rupture, for ECG waveform recordings.
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paper_title: Empirical mode decomposition based ECG enhancement and QRS detection

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In this paper an Empirical Mode Decomposition (EMD) based ECG signal enhancement and QRS detection algorithm is proposed. Being a non-invasive measurement, ECG is prone to various high and low frequency noises causing baseline wander and power line interference, which act as a source of error in QRS and other feature extraction. EMD is a fully adaptive signal decomposition technique that generates Intrinsic Mode Functions (IMF) as decomposition output. Here, first baseline wander is corrected by selective reconstruction based slope minimization technique from IMFs and then high frequency noise is removed by eliminating a noisy set of lower order IMFs with a statistical peak correction as high frequency noise elimination is accompanied by peak deformation of sharp characteristic waves. Then a set of IMFs are selected that represents QRS region and a nonlinear transformation is done for QRS enhancement. This improves detection accuracy, which is represented in the result section. Thus in this method a single fold processing of each signal is required unlike other conventional techniques.
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paper_title: ECG Signal Denoising Using Wavelet Thresholding Techniques in Human Stress Assessment

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In recent years, Electrocardiogram (ECG) plays an imperative role in heart disease diagnostics, Human Computer Interface (HCI), stress and emotional states assessment, etc. In general, ECG signals affected by noises such as baseline wandering, power line interference, electromagnetic interference, and high frequency noises during data acquisition. In order to retain the ECG signal morphology, several researches have adopted using different preprocessing methods. In this work, the stroop color word test based mental stress inducement have done and ECG signals are acquired from 10 female subjects in the age range of 20 years to 25 years. We have considered the Discrete Wavelet Transform (DWT) based wavelet denoising have incorporated using different thresholding techniques to remove three major sources of noises from the acquired ECG signals namely, power line interference, baseline wandering, and high frequency noises. Three wavelet functions ("db4", "coif5" and "sym7") and four different thresholding methods are used to denoise the noise in ECG signals. The experimental result shows the significant reduction of above considered noises and it retains the ECG signal morphology effectively. Four different performance measures were considered to select the appropriate wavelet function and thresholding rule for efficient noise removal methods such as, Signal to Interference Ratio (SIR), noise power, Percentage Root Mean Square Difference (PRD) and finally periodogramof Power Spectral Density (PSD). The experimental result shows the "coif5" wavelet andrigrsurethresholding rule is optimal for unknown Signal to Noise Ratio (SNR) in the real time ECG signals.
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paper_title: Adaptive noise cancelling: Principles and applications

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This paper describes the concept of adaptive noise cancelling, an alternative method of estimating signals corrupted by additive noise or interference. The method uses a "primary" input containing the corrupted signal and a "reference" input containing noise correlated in some unknown way with the primary noise. The reference input is adaptively filtered and subtracted from the primary input to obtain the signal estimate. Adaptive filtering before subtraction allows the treatment of inputs that are deterministic or stochastic, stationary or time variable. Wiener solutions are developed to describe asymptotic adaptive performance and output signal-to-noise ratio for stationary stochastic inputs, including single and multiple reference inputs. These solutions show that when the reference input is free of signal and certain other conditions are met noise in the primary input can be essentiany eliminated without signal distortion. It is further shown that in treating periodic interference the adaptive noise canceller acts as a notch filter with narrow bandwidth, infinite null, and the capability of tracking the exact frequency of the interference; in this case the canceller behaves as a linear, time-invariant system, with the adaptive filter converging on a dynamic rather than a static solution. Experimental results are presented that illustrate the usefulness of the adaptive noise cancelling technique in a variety of practical applications. These applications include the cancelling of various forms of periodic interference in electrocardiography, the cancelling of periodic interference in speech signals, and the cancelling of broad-band interference in the side-lobes of an antenna array. In further experiments it is shown that a sine wave and Gaussian noise can be separated by using a reference input that is a delayed version of the primary input. Suggested applications include the elimination of tape hum or turntable rumble during the playback of recorded broad-band signals and the automatic detection of very-low-level periodic signals masked by broad-band noise.
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paper_title: Peripartum and intrapartum assessment of the fetus

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Abstract Intrapartum fetal surveillance is mandatory in every labour. Although structured intermittent auscultation is useful in low-risk labour, continuous electronic fetal heart rate monitoring (CEFM) is the main method used in medium- and high-risk clinical situations. Fetal heart rate patterns are a surrogate marker of the acid–base status of the fetus. However, widespread use of CEFM during the past 30 years has not resulted in a significant decrease in the incidence of cerebral palsy or neonatal encephalopathy. This is due to a combination of factors. Very few cases of cerebral palsy arise from known causes and beyond that an even smaller number are related to intrapartum asphyxia. CEFM is technically easy to introduce but interpretation is subjective and difficult to reproduce and standardize. Lack of uniformity in the interpretation of cardiotocograph (CTG) traces is well recognized. Training of staff and the use of computerized analysis can improve reliability in interpretation. Systematic clinical approaches to CTG interpretation are described in this article. In most cases, CEFM should be used as a screening test with the addition of fetal scalp blood sampling to confirm fetal acid–base balance. This will reduce the increased rates of operative intervention associated with CEFM. Recent research has focussed on analysis of the ST segment of the fetal ECG as an adjunct to CEFM. It is useful clinically and is associated with improved obstetric and neonatal outcomes. Fetal oxygen saturation monitoring with pulse oximetry techniques may also be useful in the clinical setting.
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paper_title: Fetal electrocardiotocography in labor and neonatal outcome: An observational study in 1889 patients in the French center of Edouard Herriot, Lyon

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Background. The STAN methodology has been shown to reduce both operative delivery for fetal distress and the cord artery metabolic acidosis rate.Objective. The objective of this study was to monitor delivery modes and perinatal outcomes following the introduction of the STAN methodology and the evolution of its use at our institution.Methods. Two periods were characterized: June 2000–June 2002 (period 1) and July 2002–April 2005 (period 2). Parity, mode of labor and delivery, ST events, and neonatal outcome (Apgar score and pH of the umbilical cord artery and vein), cases of metabolic acidosis and operative delivery for fetal distress were studied.Results. One thousand eight hundred and eighty-nine women were included in the study. The rate of use of STAN increased from 13.5% to 16% over these two time periods. The rate of metabolic acidosis was low: 0.28% and 0.45%, respectively. No cases of neonatal encephalopathy or of perinatal death were diagnosed. There was a decrease in the rate of operative delive...
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paper_title: On the design of multi notch filters

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A methodology for designing FIR multi notch filters (NFs) derived from second-order prototype IIR NFs is suggested. Rejection bandwidth for the designed filter can be controlled by suitable choice of ‘r’, the pole radius of the IIR prototype NFs. The suggested multi NF can also be adapted to eliminate second-, third- and fourth-order harmonics of periodic noise besides the fundamental noise frequency component. A special case when two notch frequencies ω1 and ω2 are such that [(cosω1)(cosω2) = − 1/2] has also been discussed. The IIR multi NF design for this special case results in reduction of the number of multipliers without affecting the response of the desired NF. For the aforereferred condition, the required coefficients of impulse response of FIR multi notch filter get reduced to almost half in number resulting in reduced computations. The number of zero coefficients further reduces with increase in ‘r’ value. In addition, the frequency response becomes better, with reduced ripples in the pass bands, when ‘r’ is increased and length ‘L’ of the FIR NF is chosen appropriately. Copyright © 2010 John Wiley & Sons, Ltd.
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paper_title: Changes in the ST-interval segment of the fetal electrocardiogram in relation to acid-base status at birth

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Objective To assess the occurrence of ST-interval segment changes of the fetal electrocardiogram (ECG) and cardiotocographic (CTG) abnormalities preceding acidaemia at birth. Design Case-control study. Setting University hospital labour ward. Sample Newborns with severe cord artery metabolic acidaemia (pH /= 10 mmol/l; n= 24), moderate metabolic acidaemia (pH 7.00-7.09 and lactate >/= 10; n= 48), acidaemia (pH 7.00-7.09; n= 52), pre-acidaemia (pH 7.10-7.19; n= 265), and controls (pH >/= 7.20; n= 117). Methods Monitoring traces were assessed blinded to outcome. Main outcome measures CTG and ST changes. Results Any ST event occurred significantly more often among cases with severe (79%) and moderate (75%) metabolic acidaemia than among controls (50%). The difference was restricted to baseline T/QRS rises and to the second stage of labour, during which any event only occurred significantly more often among cases with severe metabolic acidaemia (62%) than among controls (38%). ST events coincided with abnormal CTG patterns in 67, 44, 40, and 28% of cases with severe and moderate metabolic acidaemia, acidaemia, and pre-acidaemia, respectively, and in 12% of controls. ST events with intermediary CTG were similarly frequent in the case groups (0-6%) as in the controls (4%). The ST guidelines stated intervention in 96, 62, 73, and 49% of case groups and 23% of controls. Conclusions Only two of three cases with severe and less than half of cases with moderate metabolic acidaemia were preceded by ST events coinciding with CTG abnormalities. It is therefore important to intervene for long-lasting, rapidly deteriorating or marked (preterminal) CTG abnormalities, also in the absence of ST events. (Less)
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paper_title: Harmonic adaptive noise canceler for electrocardiography with no power-line reference

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Electrocardiograms (ECGs) are of great importance as they provide plenty of information for the cardiologists. Power-line interference is a major source of distortion for ECGs. Notch filters have been proposed to reduce this kind of interference but they cannot track frequency variations and cannot reduce the power-line harmonic distortion. Adaptive canceling techniques have been proposed to track the frequency variations and reduce the harmonic distortion, yet they are dependent on sampling an external power-line reference, increasing the system complexity. In this paper we propose a modified adaptive canceler that can reduce the harmonic power-line interference without the need to sample an external power-line reference. We show that the performance of our canceler is comparable to the idealistic adaptive canceler that is dependent on sampling an external power-line signal.
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paper_title: A comparison of intrapartum automated fetal electrocardiography and conventional cardiotocography-a randomised controlled study

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OBJECTIVE ::: To examine whether intrapartum monitoring by means of automatic ST analysis (STAN) of fetal electrocardiography could reduce the rate of neonatal acidemia and the rate of operative intervention during labour, compared with monitoring by means of cardiotocography (CTG). ::: ::: ::: DESIGN ::: Randomised controlled trial. ::: ::: ::: SETTING ::: Labour ward in tertiary-level university hospital. ::: ::: ::: SAMPLE ::: A total of 1483 women in active labour with singleton term fetus in cephalic presentation. ::: ::: ::: METHODS ::: Women were randomly assigned to be monitored either by STAN or by CTG. Fetal blood sampling (FBS) was optional in both groups. ::: ::: ::: MAIN OUTCOME MEASURES ::: Neonatal acidemia (umbilical artery pH <7.10), neonatal metabolic acidosis (umbilical artery pH <7.05 and base excess <-12 mmol/l) and operative interventions: caesarean section rate, vacuum outlet (VO) rate and FBS rate. ::: ::: ::: RESULTS ::: There were no statistically significant differences between the STAN group and CTG group in the incidence of neonatal acidemia (5.8 versus 4.7%) or metabolic acidosis (1.7 versus 0.7%). The caesarean section rate (6.4 versus 4.7%) and the VO rate (9.5 versus 10.7%) were also similar in the STAN and CTG groups. The incidence of FBS was lower (P < 0.001) in the STAN group (7.0%) than in the CTG group (15.6%). ::: ::: ::: CONCLUSIONS ::: Intrapartum fetal monitoring by means of automatic STAN did not improve the neonatal outcome or decrease the caesarean section rate. However, the need for FBS during labour was lower in the STAN group.
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paper_title: Removal of power-line interference from the ECG: a review of the subtraction procedure

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BackgroundModern biomedical amplifiers have a very high common mode rejection ratio. Nevertheless, recordings are often contaminated by residual power-line interference. Traditional analogue and digital filters are known to suppress ECG components near to the power-line frequency. Different types of digital notch filters are widely used despite their inherent contradiction: tolerable signal distortion needs a narrow frequency band, which leads to ineffective filtering in cases of larger frequency deviation of the interference. Adaptive filtering introduces unacceptable transient response time, especially after steep and large QRS complexes. Other available techniques such as Fourier transform do not work in real time. The subtraction procedure is found to cope better with this problem.MethodThe subtraction procedure was developed some two decades ago, and almost totally eliminates power-line interference from the ECG signal. This procedure does not affect the signal frequency components around the interfering frequency. Digital filtering is applied on linear segments of the signal to remove the interference components. These interference components are stored and further subtracted from the signal wherever non-linear segments are encountered.ResultsModifications of the subtraction procedure have been used in thousands of ECG instruments and computer-aided systems. Other work has extended this procedure to almost all possible cases of sampling rate and interference frequency variation. Improved structure of the on-line procedure has worked successfully regardless of the multiplicity between the sampling rate and the interference frequency. Such flexibility is due to the use of specific filter modules.ConclusionThe subtraction procedure has largely proved advantageous over other methods for power-line interference cancellation in ECG signals.
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paper_title: Cardiotocography only versus cardiotocography plus ST analysis of fetal electrocardiogram for intrapartum fetal monitoring: a Swedish randomised controlled trial

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BACKGROUND ::: Previous studies indicate that analysis of the ST waveform of the fetal electrocardiogram provides information on the fetal response to hypoxia. We did a multicentre randomised controlled trial to test the hypothesis that intrapartum monitoring with cardiotocography combined with automatic ST-waveform analysis results in an improved perinatal outcome compared with cardiotocography alone. ::: ::: ::: METHODS ::: At three Swedish labour wards, 4966 women with term fetuses in the cephalic presentation entered the trial during labour after a clinical decision had been made to apply a fetal scalp electrode for internal cardiotocography. They were randomly assigned monitoring with cardiotocography plus ST analysis (CTG+ST group) or cardiotocography only (CTG group). The main outcome measure was rate of umbilical-artery metabolic acidosis (pH <7.05 and base deficit >12 mmol/L). Secondary outcomes included operative delivery for fetal distress. Results were first analysed according to intention to treat, and secondly after exclusion of cases with severe malformations or with inadequate monitoring. ::: ::: ::: FINDINGS ::: The CTG+ST group showed significantly lower rates of umbilical-artery metabolic acidosis than the cardiotocography group (15 of 2159 [0.7%] vs 31 of 2079 [2%], relative risk 0.47 [95% CI 0.25-0.86], p=0.02) and of operative delivery for fetal distress (193 of 2519 [8%] vs 227 of 2447 [9%], 0.83 [0.69-0.99], p=0.047) when all cases were included according to intention to treat. The differences were more pronounced after exclusion of 291 in the CTG+ST group and 283 in the CTG group with malformations or inadequate recording. ::: ::: ::: INTERPRETATION ::: Intrapartum monitoring with cardiotocography combined with automatic ST-waveform analysis increases the ability of obstetricians to identify fetal hypoxia and to intervene more appropriately, resulting in an improved perinatal outcome.
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paper_title: Highly narrow rejection bandwidth finite impulse response notch filters for communication

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Design of finite impulse response (FIR) notch filters (NFs) with highly narrow rejection bandwidth (RBW) is suggested. RBW is the distance between 3 dB points on the response. Reduction in the RBW is achieved progressively in three stages. In the first stage, an FIR NF is designed from a second order infinite impulse response (IIR) prototype filter. For a given length L of the NF, the authors choose maximum permissible value of ` r ' (the pole length of IIR prototype filter) to achieve very narrow RBW of the FIR filter. In the next stage, by using an amplitude change function (ACF): H ( z )(2 - H ( z )), the designed filter is sharpened. Consequently, the RBW of the resulting NF is reduced to almost half of the earlier value. This reduction of bandwidth makes the resulting NF of length 2 L . In the next stage, RBW can be further reduced by the repeated sharpening of the filter by the same ACF.
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paper_title: Harmonics estimation in emerging power system: Key issues and challenges

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Abstract The world wide increasing applications of nonlinear loads, mostly consisting of power electronics devices, have made the power quality problems a vital issue than ever before. An efficient control and mitigation of power quality parameters are highly dependent on their accurate and timely detection. Harmonics are not only one of the prime culprits that deteriorate power quality of the supply system but it also affects accurate estimation and effective control of power quality problems. In this paper, several methods of power system harmonics estimation are critically reviewed and classified based on the type of analysis tool and applications. Various estimation techniques are discussed in brief; comparison of available approaches are examined and presented. The key issues and challenges in harmonics estimations are highlighted. A vast collection of papers, books and standards are listed in the reference list, which is useful to the researchers, engineers and policy-makers in the area of power quality.
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paper_title: ECG signal denoising by wavelet transform thresholding

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In recent years, ECG signal plays an important role in the primary diagnosis, prognosis and survival analysis of heart diseases. In this paper a new approach based on the threshold value of ECG signal determination is proposed using Wavelet Transform coefficients. Electrocardiography has had a profound influence on the practice of medicine. The electrocardiogram signal contains an important amount of information that can be exploited in different manners. The ECG signal allows for the analysis of anatomic and physiologic aspects of the whole cardiac muscle. Different ECG signals are used to verify the proposed method using MATLAB software. Method presented in this paper is compared with the Donoho's method for signal denoising meanwhile better results are obtained for ECG signals by the proposed algorithm.
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paper_title: A modified adaptive noise canceler for electrocardiography with no power-line reference

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Power-line interference can severely distort electrocardiographs (ECGs). Several techniques have been proposed to eliminate the power-line interference without affecting the ECGs. One of the well-established techniques is the Adaptive Noise Canceler (ANC). In this paper we propose an improvement to the ANC by eliminating the need to sample an external power-line reference. The proposed method is shown to be comparable in performance to the ANC. It is therefore possible to implement the proposed canceler in software without the need to change the acquisition hardware system as was previously needed by the ANC.
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paper_title: PCA and ICA processing methods for removal of artifacts and noise in electrocardiograms: A survey and comparison

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Electrocardiogram (ECG) signals are affected by various kinds of noise and artifacts that may hide important information of interest. Wavelet transform (WT) technique is used to identify the characteristic points of the electrocardiogram (ECG) signal with fairly good accuracy, even in the presence of severe high frequency and low frequency noise. Independent component analysis (ICA) is a new technique suitable for separating independent components from ECG complex signals, whereas principal component analysis (PCA) is used to reduce dimensionality and for feature extraction of the ECG data prior to or at times after performing ICA in special circumstances. In this analysis, PCA is analyzed from three points of view, variance maximization, the singular value decomposition and ECG data compression. The sensitivity of the different ECG components with respect to the ECG data dimensions has been studied using PCA screen plots. The validity and performance of the approaches used are confirmed through computer simulations on common standards for electrocardiography (CSE) base ECG data. Standard or instantaneous ICA, which is the most commonly, accepted ICA technique is first compared with PCA technique and then with constrained ICA, which enables the estimation of only one component close to a particular reference ECG signal. The ICA method can also be extended for QRS detection and reference signal generation, using constrained ICA and as well for multichannel ECG separation after removing noise and artifacts, further favoring segment classification. The results were obtained using Matlab environment. Using composite WT based PCA-ICA methods helps for redundant data reduction as well for better feature extraction. The efficacy of the combined PCA-ICA algorithm lies on the fact that the location of the R-peaks is accurately determined, and none of the peaks are ignored or missed, as Quadratic Spline wavelet is also used.
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paper_title: Efficient block-wise independent component analysis with optimal learning rate

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Abstract Independent component analysis (ICA) is a potential solution for blind source separation (BSS) problems and has proven to be effective in many practical applications. One major drawback for ICA algorithms is its heavy computation load which is especially deteriorated in long-term signals. To solve this problem, the block-wise approach is proposed to improve the computational efficiency in this study. As ambiguities of variances and order of the separated components exist for ICA algorithms, signal reconstruction is an issue for block-wise approach. In this study, correlation coefficients (CC) of the short-term Fourier transform (STFT) among those acquired from the neighboring blocks are adopted for order permutation and phase correction of the separated signals. The weights of the separated signals are then normalized by the maximum amplitude of the corresponding one in previous block to avoid the variance ambiguity. Two robust ICA algorithms based on iterative matrix inversion approach, one with fixed nonlinear functions whereas another one with flexibly selected nonlinear functions, are implemented in both batch and block-wise processing for performance evaluation. Linearly mixed biopotential signals (ECG and EMG) and 60-Hz sinusoid are incorporated for the experiments. The results reveal that the proposed block-wise approach can attain the desired requirements in a more efficient way without loss of the separation performance. The proposed approach may be a potential tool for which the computational efficiency is an important issue.
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paper_title: Comparison of Doppler ultrasound and direct electrocardiography acquisition techniques for quantification of fetal heart rate variability

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A method for comparison of two acquisition techniques that are applied in clinical practice to provide information on fetal condition is presented. The aim of this work was to evaluate the commonly used Doppler ultrasound technique for monitoring of mechanical activity of fetal heart. Accuracy of beat-to-beat interval determination together with its influence on indices describing the fetal heart rate (FHR) variability calculated automatically using computer-aided fetal monitoring system were examined. We considered the direct fetal electrocardiography as a reference technique because it ensures the highest possible accuracy of heart interval measurement, and additionally all the definitions of popular time domain parameters quantifying FHR variability formerly have been created using the fetal electrocardiogram. We evaluated the reliability of various so called short-term and long-term variability indices, when they are calculated automatically using the signal obtained via the Doppler US from a fetal monitor. The results proved that evaluation of the acquisition technique influence on fetal well-being assessment cannot be accomplished basing on direct measurements of heartbeats only. The more relevant is the estimation of accuracy of the variability indices, since analysis of their changes can significantly increase predictability of fetal distress
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paper_title: Monitoring the fetal heart non-invasively: a review of methods

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Doppler ultrasound, ultrasound M-mode analysis, fetal electrocardiography, and fetal magnetocardiography are methods by which the fetal heart can be monitored non-invasively. In this paper, they are evaluated and compared. Customarily, it is solely the fetal heart rate, which is monitored using the Doppler ultrasound technique since it is both simple to use and cheap. However, this method inherently produces an averaged heart rate and therefore cannot give the beat-to-beat variability. Fetal electrocardiography has similar advantages, but in addition offers the potential for monitoring beat-to-beat variability and performing electrocardiogram morphological analysis. Its disadvantage is that its reliability is only 60%, although it is the only technique that offers truly long-term ambulatory monitoring. Ultrasound M-mode analysis allows a estimation of atrial and ventricular coordination, as well as an estimation of PR intervals. Bradycardias, supraventricular tachycardias, extra systoles are readily diagnosed using this method although timing will be inaccurate. Fetal magnetocardiograms can be detected reliably and used for accurate beat-to-beat measurements and morphological analysis. Consequently, they can be used for the classification of arrhythmias and the diagnosis of a long QT syndrome and some congenital heart diseases.
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paper_title: Effect of availability of fetal ECG monitoring on operative deliveries

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Objective. The objective of our study was to test the hypothesis that the availability and selective use of STAN® in conjunction with cardiotocography for intrapartum monitoring, lowers the incidence of operative deliveries for fetal distress. Design. Observational study. Setting. Delivery suite of the National University Hospital, Singapore. Methods. The data regarding intrapartum cesarean sections and instrumental vaginal deliveries for presumed fetal distress and the condition of the neonate at birth (Apgar scores at one and five minutes and admission to neonatal intensive care unit (NICU) were collected over two consecutive three-year periods. In the first triennium, only external cardiotocography was used for intrapartum fetal surveillance and in the second triennium STAN® monitoring was available for use in the delivery suite. Results. With the availability and selective use of STAN® monitoring, there was a significant decrease in the number of instrumental deliveries for fetal distress (from 66 out...
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paper_title: Digital $Q$-Varying Notch IIR Filter With Transient Suppression

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In many measurement applications, it is required to have notch filters that simultaneously possess a very selective magnitude response (high quality factor Q) and a transient response of short duration. However, increasing the quality factor also increases the duration of the transient process in the filter after the action of the excitation. This paper presents a new concept of digital IIR notch filters, whose quality factor changes with time. Owing to a temporary change in the value of the quality factor, the transient can considerably be reduced. Simulations verifying the effectiveness of the proposed Q-varying IIR notch filter are presented and compared with the performance of the traditional Q-constant filter using ECG signals with unwanted sinusoidal interference as a study case.
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paper_title: An Improved Adaptive Power Line Interference Canceller for Electrocardiography

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Power line interference may severely corrupt a biomedical recording. Notch filters and adaptive cancellers have been suggested to suppress this interference. We propose an improved adaptive canceller for the reduction of the fundamental power line interference component and harmonics in electrocardiogram (ECG) recordings. The method tracks the amplitude, phase, and frequency of all the interference components for power line frequency deviations up to about 4 Hz. A comparison is made between the performance of our method, former adaptive cancellers, and a narrow and a wide notch filter in suppressing the fundamental power line interference component. For this purpose a real ECG signal is corrupted by an artificial power line interference signal. The cleaned signal after applying all methods is compared with the original ECG signal. Our improved adaptive canceller shows a signal-to-power-line-interference ratio for the fundamental component up to 30 dB higher than that produced by the other methods. Moreover, our method is also effective for the suppression of the harmonics of the power line interference
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paper_title: Plymouth randomized trial of cardiotocogram only versus ST waveform plus cardiotocogram for intrapartum monitoring in 2400 cases.

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OBJECTIVE ::: The physiology of changes in the ST waveform of the fetal electrocardiogram has been elucidated in extensive animal and human observational studies. A combination of heart rate and ST waveform analysis might improve the predictive value of intrapartum monitoring. Our purpose was to compare operative intervention and neonatal outcome in labors monitored by the conventional cardiotocogram with those monitored by ST waveform plus the cardiotocogram. ::: ::: ::: STUDY DESIGN ::: A prospective, randomized clinical trial was performed on 2434 high-risk labors in a district general hospital in Plymouth, England. Statistical analysis was performed by Student t test and chi 2 analysis. ::: ::: ::: RESULTS ::: There was a 46% reduction (p < 0.001, odds ratio 1.85 [1.35-2.66]) in operative deliveries for "fetal distress" and a trend to less metabolic acidosis (p = 0.09, odds ratio 0.38 [0.13-1.07]) and fewer low 5-minute Apgar scores (p = 0.12, odds ratio 0.62 [0.35-1.08]) in the ST waveform plus cardiotocogram arm. ::: ::: ::: CONCLUSIONS ::: ST waveform analysis discriminates cardiotocogram changes in labor, and the protocol for interpretation is safe. Further randomized studies are warranted.
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paper_title: A French randomized controlled trial of ST-segment analysis in a population with abnormal cardiotocograms during labor.

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OBJECTIVE ::: The purpose of this study was to assess whether knowledge of ST-segment analysis was associated with a reduction in operative deliveries for nonreassuring fetal status (NRFS) or with a need for at least 1 scalp pH during labor. ::: ::: ::: STUDY DESIGN ::: Seven hundred ninety-nine women at term with abnormal cardiotocography or meconium-stained amniotic fluid (7%) were assigned randomly to the intervention group (cardiotocography + STAN) or the control group (cardiotocography) in 2 university hospitals in Strasbourg, France. Scalp pH testing was optional in both groups. Abnormal neonatal outcome was pH <7.05 or umbilical cord blood artery base deficit of >12 or a 5-min Apgar score of <7 or neonatal intensive care unit admission or convulsions or neonatal death. Study power was 80% for the detection of a prespecified reduction from 50%-40% in operative delivery for NRFS. ::: ::: ::: RESULTS ::: The operative delivery (cesarean or instrumental) rate for NRFS did not differ between the 2 groups: 33.6% (134/399) in the cardiotocography + STAN analysis group vs 37% (148/400) in the cardiotocography group (relative risk, 0.91; 95% CI, 0.75-1.10). The rate of operative delivery for dystocia was also similar in both groups. The percentage of women whose fetus had at least 1 scalp pH measurement during labor was substantially lower in the group with ST-segment analysis: 27% compared with 62% (relative risk, 0.44; 95% CI, 0.36-0.52). Neonatal outcomes did not differ significantly between groups. ::: ::: ::: CONCLUSION ::: In a population with abnormal cardiotocography in labor, cardiotocography combined with ST-segment analysis was not associated with a reduction in operative deliveries for NRFS. The proportion of infants without scalp pH sampling during labor increased substantially, however.
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paper_title: Clinical outcomes of high-risk labours monitored using fetal electrocardiography.

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Objectives: The aim of the study was to review clinical and laboratory outcomes of a cohort of fetuses monitored during high-risk labours, simultaneously by fetal electrocardiography (FECG) and routine cardiotocography (CTG). Materials and Methods: Eighty-three parturients from the Department of Obstetrics and Gynecology of Medical University were included in the clinical study. Inclusive criteria to the study group were: (i) singleton pregnancy at term (between 37 and 42 weeks’ gestation), (ii) longitudinal fetal lying, (iii) more than 2500 g of estimated fetal weight, (iv) meconium-stained liquor, and (v) induction of labour due to fetal indications. Fetal outcome parameters analysed included Apgar scores at 1st, 5th and 10th minute after birth, cord artery acid-base assessment and lactate concentrations analysis. FECG was performed during labour, until the neonate was born, with the use of single spiral scalp electrode connected to the STAN S21 heart monitor. Immediately after delivery, arterial cord blood gas and venous cord blood lactate’s concentrations were analysed. Results: The sensitivity (100%), specifi city (97%), negative predictive value (NPV) (100%) and positive predictive value (33%) were higher for FECG than for CTG. Moreover, several signifi cant correlations between episodic/baseline T/QRS ratio rises and cord artery acid-base as well as lactate concentrations were demonstrated. Conclusions: Correlations between episodic/baseline T/QRS ratio rises and fetal outcome parameters indicate that observed changes in FECG refl ect neonatal metabolic lactate acidosis. The high sensitivity, specifi city and especially very high NPV are proof that FECG serves as a reliable method for electronic fetal monitoring during high-risk labours. Ann Acad Med Singapore 2010;39:27-32
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paper_title: A frequency domain Hampel filter for blind rejection of sinusoidal interference from electromyograms

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A frequency domain filtering method is presented for the removal of power-line and other sinusoidal interference from electromyograms. The presence of such interference results in spikes in the complex-valued fast Fourier transform which can be considered to be outliers. The filter uses the outlier-robust Hampel identifier to detect spikes and replaces them with the median value of local values. The performance of the filter was tested using a set of simulated electromyograms and on experimental data. It was shown that the filter is more effective at rejecting interference than multiple notch filtering and spectral interpolation. The main advantages of using this method are that the frequencies at which the interference occurs need not be known a priori and that signals are not distorted in the absence of interference. In the case of single-frequency interference added to simulated and experimental data, errors in root-mean-squared amplitude and median frequency of <5% are reported.
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paper_title: Least-Mean-Square algorithm based adaptive filters for removing power line interference from ECG signal

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The 50 Hz power line is one of the main sources of interference in ECG signal measurement, and it distorts the original ECG signal while recording. Recently, adaptive filtering has become one of the effective and popular methods for the processing and analysis of the ECG signal. In this study, we have used adaptive filters to remove the power line interference from the ECG signal. We have used different adaptive filter algorithms, such as, Least-Mean-Square (LMS), Block LMS (BLMS), Delay LMS (DLMS), Adjoint LMS, Filtered-X (XLMS), Normalized LMS (NLMS) and Fast Fourier Transform BLMS (FFT BLMS). We have used the Signal Processing Toolbox of the mentioned algorithms built in MATLAB®. It reveals that among all the adaptive filters, the adaptive NLMS filter removes the 50 Hz power line interference more effectively.
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paper_title: Ensemble empirical mode decomposition based feature enhancement of cardio signals

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Abstract This paper presents an application of ensemble empirical mode decomposition method for enhancement of specific biological signal features. The application for two types of cardiological signals is presented in this article. Detection of fiducial points is a routine task for analyzing these signals. In a clinical situation, cardiological signals are usually corrupted by artifacts and finding exact time instances of various fiducial points is a challenge. Filtering approach for signal to noise ratio enhancing is traditionally and widely used in clinical practice. Methods, based on filtering, however, have serious limitations when it is necessary to find compromise between noise suppression and preservation of signal features. The proposed method uses ensemble empirical mode decomposition in order to suppress noise or enhance specific waves in the signal. Performance of the method was estimated by using clinical electrocardiogram and impedance cardiogram signals with synthetic baseline-wander, power-line and added Gaussian noise. In electrocardiogram application, an average estimation error of QRS complex length was 2.06–4.47%, the smallest in comparison to the reference methods. In impedance cardiogram application, the proposed method provided the highest cross-correlation coefficient between original and de-noised signal in comparison to reference methods. When the signal to noise ratio of the input signal was −12 dB, the method provided signal to error ratio of 33 dB in this case. The proposed method is adaptive to template and signal itself and thus could be applied to other non-stationary biological signals.
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paper_title: Linear and nonlinear parameters for the analysisof fetal heart rate signal from cardiotocographic recordings

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Antepartum fetal monitoring based on the classical cardiotocography (CTG) is a noninvasive and simple tool for checking fetal status. Its introduction in the clinical routine limited the occurrence of fetal problems leading to a reduction of the precocious child mortality. Nevertheless, very poor indications on fetal pathologies can be inferred from the even automatic CTG analysis methods, which are actually employed. The feeling is that fetal heart rate (FHR) signals and uterine contractions carry much more information on fetal state than is usually extracted by classical analysis methods. In particular, FHR signal contains indications about the neural development of the fetus. However, the methods actually adopted for judging a CTG trace as "abnormal" give weak predictive indications about fetal dangers. We propose a new methodological approach for the CTG monitoring, based on a multiparametric FHR analysis, which includes spectral parameters from autoregressive models and nonlinear algorithms (approximate entropy). This preliminary study considers 14 normal fetuses, eight cases of gestational (maternal) diabetes, and 13 intrauterine growth retarded fetuses. A comparison with the traditional time domain analysis is also included. This paper shows that the proposed new parameters are able to separate normal from pathological fetuses. Results constitute the first step for realizing a new clinical classification system for the early diagnosis of most common fetal pathologies.
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paper_title: Harmonic-free line-commutated ac/dc rectifiers

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In this paper both a method and apparatus are applied to different configurations of line-commutated ac/dc rectifiers to reduce the distortion of currents flowing from the ac supply. The load may be either inductive or capacitive. The technology involves an accurate shaping of the dc current by using two self-commutated switches. This dc-current shaping is reflected back into the shaping of the ac input currents, which become pure sine waves. Thyristor-based rectifying operation is possible with a simple control circuit, which is able to deal with both rapid load variations and failures in the self-commutated switches. Furthermore, the overlap conduction of bridge thyristors is eliminated completely. Experimental verification is provided from a 400-V 30-kVA 50-Hz laboratory prototype.
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paper_title: Mitigation method of 3rd-harmonic voltage for a three-phase four-wire distribution system based on a series active filter for the neutral conductor

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This paper proposes a series active filter for mitigation of the 3rd-harmonic voltage in a three-phase four-wire power distribution system in a building. The active filter which consists of a single-phase inverter can suppress the harmonic voltage of the system. The active filter is characterized by acting not only as a capacitor but also as a resistor for the 3rd-harmonic components. A Hilbert transformer is applied to the controller of the active filter in order to realize the accurate 3rd-harmonic detection on a single-phase active filter. Measurement results of harmonic distortion of source voltage in a building are also shown in this paper. It is clarified in a simulation and experiment that the active filter can suppress the 3rd-harmonic voltage without increasing neutral conductor current.
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paper_title: Reduced prevalence of metabolic acidosis at birth: an analysis of established STAN usage in the total population of deliveries in a Swedish district hospital

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OBJECTIVE: The purpose of this study was to investigate quality-of-care improvements after the introduction of ST waveform analysis as an adjunct to standard cardiotocography (CTG). STUDY DESIGN: This was a prospective clinical study that was conducted over 7 years. Four yearly cohorts of 12,832 term pregnancies were part of a detailed analysis. Cord blood metabolic acidosis and neonatal outcome were main outcome measures. RESULTS: The STAN (S31 Fetal Heart Monitor; Neoventa Medical AB, Molndal, Sweden) usage rate increased from 26 to 69%. The cord metabolic acidosis rate was reduced from 0.72 to 0.06%. This 91.7% improvement was associated with a significant reduction in the number of cases with a prolonged response time, calculated as the time from CTG + ST indications to intervene until delivery and an ability of the staff to identify and act on preterminal and unstable fetal heart rate patterns at the onset of a recording. CONCLUSION: Our data indicate a paradigm shift in the outcome of delivery related to a high rate of CTG + ST usage and the application of structured CTG analysis.
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paper_title: STAN in clinical practice--the outcome of 2 years of regular use in the city of Gothenburg.

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OBJECTIVE ::: The purpose of this study was to monitor the introduction of the STAN-methodology (Noventa Medical, Moelndal, Sweden). ::: ::: ::: STUDY DESIGN ::: This was a prospective observational study covering the total population of deliveries at term during 2 years. Four thousand eight hundred and thirty out of 14,687 term pregnancies were monitored using the STAN S 21 fetal heart monitor and the associated clinical guidelines. Cord artery metabolic acidosis, neonatal outcome, and rates of operative deliveries for fetal distress were assessed. ::: ::: ::: RESULTS ::: The annual rate of STAN usage increased from 28.1% to 37.7% and was associated with a significant reduction in metabolic acidosis rate in the total population from 0.76% to 0.44% (P < .05). The compliance with the clinical guidelines increased in cases requiring intervention. The rates for moderate/severe hypoxic neonatal encephalopathy were consistently low, 0.55 and 0.68 per 1000 deliveries, respectively, and corresponding to previous findings. The rate of operative delivery did not change during the 2 years in the total population. ::: ::: ::: CONCLUSION ::: Increasing STAN usage provided consistent improvements in fetal outcome equalling those noted in the Swedish randomized controlled trial (RCT) without increasing operative interventions for fetal distress.
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paper_title: 60-Hz Interference in Electrocardiography

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One of the major problems encountered in recording ECG's is the appearance of unwanted 60-Hz interference in the output. This paper examines the many possible sources of interference, and for each provides a description, an identifying test, and a remedy. Then we look at possible equipment imperfections and guidelines for amplifier design to aid in the evaluation of new developments in the field of electrocardiography. As an illustrative example, we apply the procedure for isolating the source of interference to an exposition display in which each visitor could rapidly view his own ECG.
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paper_title: Power line interference filtering on surface electromyography based on the stationary wavelet packet transform

paper_content:

Power line interference is one of the main problems in surface electromyogram signals (EMG) analysis. In this work, a new method based on the stationary wavelet packet transform is proposed to estimate and remove this kind of noise from EMG data records. The performance has been quantitatively evaluated with synthetic noisy signals, obtaining good results independently from the signal to noise ratio (SNR). For the analyzed cases, the obtained results show that the correlation coefficient is around 0.99, the energy respecting to the pure EMG signal is 98-104%, the SNR is between 16.64 and 20.40dB and the mean absolute error (MAE) is in the range of -69.02 and -65.31dB. It has been also applied on 18 real EMG signals, evaluating the percentage of energy respecting to the noisy signals. The proposed method adjusts the reduction level to the amplitude of each harmonic present in the analyzed noisy signals (synthetic and real), reducing the harmonics with no alteration of the desired signal.
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paper_title: An adaptive filtering approach for electrocardiogram (ECG) signal noise reduction using neural networks

paper_content:

Abstract Electrocardiogram (ECG) signals have been widely used in clinical studies to detect heart diseases. However, ECG signals are often contaminated with noise such as baseline drift, electrode motion artifacts, power-line interference, muscle contraction noise, etc. Conventional methods for ECG noise removal do not yield satisfactory results due to the non-stationary nature of the associated noise sources and their spectral overlap with desired ECG signals. In this paper, an adaptive filtering approach based on discrete wavelet transform and artificial neural network is proposed for ECG signal noise reduction. This new approach combines the multi-resolution property of wavelet decomposition and the adaptive learning ability of artificial neural networks, and fits well with ECG signal processing applications. Computer simulation results demonstrate that this proposed approach can successfully remove a wide range of noise with significant improvement on SNR (signal-to-noise ratio).
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paper_title: The use of STAN monitoring in the labour ward.

paper_content:

Continuous intrapartum cardiotocography (CTG) augmented by fetal ECG ST segment analysis (STAN) has the potential to reduce the rates of neonatal metabolic acidosis and obstetric interventions. STAN was introduced at Ninewells Hospital, Dundee in October 2007. Data were collected prospectively from all women who received continuous intrapartum CTG and STAN between 1 October 2007 and 31 March 2008. A total of 253 women had continuous CTG and STAN. The median number of ST events was one (range = 1–32). Most (556/719, 77%) ST events were associated with a normal CTG; 46/144 (32%) patients with an ST event required immediate action. Three of the 253 (1.2%) women were delivered based on an ST event with a normal CTG; four (1.5%) had severe neonatal metabolic acidosis and all four cases had intrapartum ST events and were not managed according to STAN guidelines. ST events are common but the majority of ST events require no action. The high incidence of false-positive ST events might have contributed to the fail...
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paper_title: Subtraction procedure for powerline interference removing from ECG: improvement for non-multiple sampling.

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This paper presents an improvement of the subtraction procedure for interference cancellation in ECG. In contrast to the well-known hardware and software filters, the procedure does not affect the signal frequency components around the rated powerline frequency. Originally, the procedure was developed for multiplicity between the sampling rate and the interference frequency. We analysed and improved the procedure structure in cases of non-multiple sampling, introducing a set of specially designed filters. Thus the implementation of the subtraction procedure is extended to almost all possible cases of sampling rate and interference frequency variation. The procedure has been adapted for online implementation. The research was initially carried out in a MATLAB environment. Further, programmes have been written in C + + language for digital signal processors and personal computers. The results obtained with real ECG signals show high efficiency of the interference cancellation.
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paper_title: Detection and Processing Techniques of FECG Signal for Fetal Monitoring

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Fetal electrocardiogram (FECG) signal contains potentially precise information that could assist clinicians in making more appropriate and timely decisions during labor. The ultimate reason for the interest in FECG signal analysis is in clinical diagnosis and biomedical applications. The extraction and detection of the FECG signal from composite abdominal signals with powerful and advance methodologies are becoming very important requirements in fetal monitoring. The purpose of this review paper is to illustrate the various methodologies and developed algorithms on FECG signal detection and analysis to provide efficient and effective ways of understanding the FECG signal and its nature for fetal monitoring. A comparative study has been carried out to show the performance and accuracy of various methods of FECG signal analysis for fetal monitoring. Finally, this paper further focused some of the hardware implementations using electrical signals for monitoring the fetal heart rate. This paper opens up a passage for researchers, physicians, and end users to advocate an excellent understanding of FECG signal and its analysis procedures for fetal heart rate monitoring system.
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paper_title: Robust suppression of nonstationary power-line interference in electrocardiogram signals.

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It is a challenge to suppress time-varying power-line interference (PLI) with various levels in electrocardiogram (ECG) signals. Most previous attempts of tracking and suppressing the nonstationary PLI signal are based on the least-squares (LS) algorithm. This makes these methods susceptible to QRS complex in suppressing a low-level PLI signal which is frequently coupled in battery-operated ECG equipment. To address the limitation of LS-based methods, this study presents a robust PLI suppression system based on a robust extension of the Kalman filter. In addition, we used an improved version of empirical mode decomposition to further attenuate the QRS complex. Experiments show that our system could effectively suppress the PLI while preserving meaningful ECG components at various interference levels.
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paper_title: Denoising of ECG signals based on noise reduction algorithms in EMD and wavelet domains

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Abstract This paper presents a new ECG denoising approach based on noise reduction algorithms in empirical mode decomposition (EMD) and discrete wavelet transform (DWT) domains. Unlike the conventional EMD based ECG denoising approaches that neglect a number of initial intrinsic mode functions (IMFs) containing the QRS complex as well as noise, we propose to perform windowing in the EMD domain in order to reduce the noise from the initial IMFs instead of discarding them completely thus preserving the QRS complex and yielding a relatively cleaner ECG signal. The signal thus obtained is transformed in the DWT domain, where an adaptive soft thresholding based noise reduction algorithm is employed considering the advantageous properties of the DWT compared to that of the EMD in preserving the energy in the presence of noise and in reconstructing the original ECG signal with a better time resolution. Extensive simulations are carried out using the MIT-BIH arrythmia database and the performance of the proposed method is evaluated in terms of several standard metrics. The simulation results show that the proposed method is able to reduce noise from the noisy ECG signals more accurately and consistently in comparison to some of the stateof-the-art methods.
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paper_title: A review of electrocardiogram filtering

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Abstract Analog filtering and digital signal processing algorithms in the preprocessing modules of an electrocardiographic device play a pivotal role in providing high-quality electrocardiogram (ECG) signals for analysis, interpretation, and presentation (display, printout, and storage). In this article, issues relating to inaccuracy of ECG preprocessing filters are investigated in the context of facilitating efficient ECG interpretation and diagnosis. The discussion covers 4 specific ECG preprocessing applications: anti-aliasing and upper-frequency cutoff, baseline wander suppression and lower-frequency cutoff, line frequency rejection, and muscle artifact reduction. Issues discussed include linear phase, aliasing, distortion, ringing, and attenuation of desired ECG signals. Due to the overlapping power spectrum of signal and noise in acquired ECG data, frequency selective filters must seek a delicate balance between noise removal and deformation of the desired signal. Most importantly, the filtering output should not adversely impact subsequent diagnosis and interpretation. Based on these discussions, several suggestions are made to improve and update existing ECG data preprocessing standards and guidelines.
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paper_title: Suppressing harmonic powerline interference using multiple-notch filtering methods with improved transient behavior

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Abstract In signal processing it is often required to have multiple-notch filters which simultaneously possess a very selective magnitude response and a transient response of short duration. Multiple-notch filters are usually used to remove the powerline hum and its harmonics. It is known, that sharper notches are obtained by either using more coefficients in FIR filters, or by placing the pole closer to the unit circle in IIR filters. However, increasing the filter selectivity also increases the duration of the transient process in the filter after the action of the excitation. This paper presents and compares two methods for suppressing the transient response in multiple-notch filters. As an example, these methods have been used to eliminate the powerline noise from the ECG signal. Both filtering techniques are characterized by improved transient behavior compared to the traditional multiple-notch filters. In the first part of the paper a concept of digital IIR multiple-notch filters whose pole radius changes with time is proposed. Owing to a temporary change in the value of the pole radius, the transient can be considerably reduced. In the second part of this review the technique which uses the vector projection to find better initial values for time-invariant multiple-notch filter is presented. Simulations verifying the effectiveness of the proposed IIR multiple-notch filter with time-varying pole radius and the filter with non-zero initial conditions are presented and compared to the performance of the traditional time-invariant filter using an ECG signal with unwanted fixed-frequency harmonic interferences as a study case.
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paper_title: On the design of multi notch filters

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A methodology for designing FIR multi notch filters (NFs) derived from second-order prototype IIR NFs is suggested. Rejection bandwidth for the designed filter can be controlled by suitable choice of ‘r’, the pole radius of the IIR prototype NFs. The suggested multi NF can also be adapted to eliminate second-, third- and fourth-order harmonics of periodic noise besides the fundamental noise frequency component. A special case when two notch frequencies ω1 and ω2 are such that [(cosω1)(cosω2) = − 1/2] has also been discussed. The IIR multi NF design for this special case results in reduction of the number of multipliers without affecting the response of the desired NF. For the aforereferred condition, the required coefficients of impulse response of FIR multi notch filter get reduced to almost half in number resulting in reduced computations. The number of zero coefficients further reduces with increase in ‘r’ value. In addition, the frequency response becomes better, with reduced ripples in the pass bands, when ‘r’ is increased and length ‘L’ of the FIR NF is chosen appropriately. Copyright © 2010 John Wiley & Sons, Ltd.
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paper_title: Elimination of AC interference in electrocardiogram using IIR notch filter with transient suppression

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A technique for suppressing the transient states of IIR notch filter is investigated. This technique uses the vector projection to find better initial values for notch filters. When a notch or comb filter is used to eliminate power line (AC) interference in the recording of electrocardiograms (ECG), the performance of the notch filter with transient suppression is better than that of the conventional notch filter with arbitrary initial condition. The improvements with this technique are at the cost of additional computation load at the beginning of filtering.<<ETX>>
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paper_title: Design of IIR multiple notch filters

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A new method for designing IIR multiple notch filters is presented, which satisfies the notch frequency specifications exactly and realizes 3 dB rejection bandwidths which are lower than those specified. An allpass filter-based realization has been worked out to make the design relatively insensitive to coefficient inaccuracies. Illustrative examples are given.
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paper_title: Adaptive noise cancelling: Principles and applications

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This paper describes the concept of adaptive noise cancelling, an alternative method of estimating signals corrupted by additive noise or interference. The method uses a "primary" input containing the corrupted signal and a "reference" input containing noise correlated in some unknown way with the primary noise. The reference input is adaptively filtered and subtracted from the primary input to obtain the signal estimate. Adaptive filtering before subtraction allows the treatment of inputs that are deterministic or stochastic, stationary or time variable. Wiener solutions are developed to describe asymptotic adaptive performance and output signal-to-noise ratio for stationary stochastic inputs, including single and multiple reference inputs. These solutions show that when the reference input is free of signal and certain other conditions are met noise in the primary input can be essentiany eliminated without signal distortion. It is further shown that in treating periodic interference the adaptive noise canceller acts as a notch filter with narrow bandwidth, infinite null, and the capability of tracking the exact frequency of the interference; in this case the canceller behaves as a linear, time-invariant system, with the adaptive filter converging on a dynamic rather than a static solution. Experimental results are presented that illustrate the usefulness of the adaptive noise cancelling technique in a variety of practical applications. These applications include the cancelling of various forms of periodic interference in electrocardiography, the cancelling of periodic interference in speech signals, and the cancelling of broad-band interference in the side-lobes of an antenna array. In further experiments it is shown that a sine wave and Gaussian noise can be separated by using a reference input that is a delayed version of the primary input. Suggested applications include the elimination of tape hum or turntable rumble during the playback of recorded broad-band signals and the automatic detection of very-low-level periodic signals masked by broad-band noise.
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paper_title: A nonlinear adaptive method of elimination of power line interference in ECG signals

paper_content:

A new method of elimination of power line noise in electrocardiogram signals is presented. The proposed method employs, as its main building block, a recently developed signal processing algorithm capable of extracting a specified component of a signal and tracking its variations over time. Design considerations and performance of the proposed method are presented with the aid of computer simulations. Superior performance is observed in terms of effective elimination of noise under conditions of varying powerline interference frequency. The proposed method presents a simple and robust structure which complies with practical constraints involved in the problem such as low computational resource availability and low sampling frequency.
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paper_title: The Elimination of 50 Hz Power Line Interference from ECG Using a Variable Step Size LMS Adaptive Filtering Algorithm

paper_content:

This article demonstrates" a new variable step size LMS adaptive filtering algorithm" to eliminate 50 Hz power line interference. This approach can provide faster convergencerate and smaller mean square error (MSE). (Life ScienceJournal. 2006;3(4) :90 - 93) (ISSN: 1097- 8135).
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paper_title: Removing harmonic power line interference from biopotential signals in low cost acquisition systems

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This paper presents a new proposal of a very low cost and highly efficient interference canceller to be applied to biomedical signals. The power line reference is obtained from analog to digital conversion while higher harmonics are mathematically estimated by means of trigonometric relations. These signals are processed by an adaptive algorithm in order to suppress harmonic interference. Biomedical acquisition systems that incorporate a conventional adaptive canceller, whose reference signal is sampled from power line, can be easily modified to improve interference suppression without hardware modifications. Real application examples are supplied in order to demonstrate its usefulness in electroencephalographic, electrocardiographic and auditory evoked potential signals.
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paper_title: An Improved Adaptive Power Line Interference Canceller for Electrocardiography

paper_content:

Power line interference may severely corrupt a biomedical recording. Notch filters and adaptive cancellers have been suggested to suppress this interference. We propose an improved adaptive canceller for the reduction of the fundamental power line interference component and harmonics in electrocardiogram (ECG) recordings. The method tracks the amplitude, phase, and frequency of all the interference components for power line frequency deviations up to about 4 Hz. A comparison is made between the performance of our method, former adaptive cancellers, and a narrow and a wide notch filter in suppressing the fundamental power line interference component. For this purpose a real ECG signal is corrupted by an artificial power line interference signal. The cleaned signal after applying all methods is compared with the original ECG signal. Our improved adaptive canceller shows a signal-to-power-line-interference ratio for the fundamental component up to 30 dB higher than that produced by the other methods. Moreover, our method is also effective for the suppression of the harmonics of the power line interference
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paper_title: Infomax and maximum likelihood for blind source separation

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Algorithms for the blind separation of sources can be derived from several different principles. This article shows that the infomax (information-maximization) principle is equivalent to the maximum likelihood. The application of the infomax principle to source separation consists of maximizing an output entropy.
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paper_title: Sensor Array and Electrode Selection for Non-invasive Fetal Electrocardiogram Extraction by Independent Component Analysis

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Recently, non-invasive techniques to measure the fetal electrocardiogram (FECG) signal have given very promising results. However, the important question of the number and the location of the external sensors has been often discarded. In this paper, an electrode-array approach is proposed; it is combined with a sensor selection algorithm using a mutual information criterion. The sensor selection algorithm is run in parallel to an independent component analysis of the selected signals. The aim of this method is to make a real time extraction of the FECG possible. The results are shown on simulated biomedical signals.
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paper_title: Noninvasive fetal electrocardiogram extraction: blind separation versus adaptive noise cancellation

paper_content:

The problem of the fetal electrocardiogram (FECG) extraction from maternal skin electrode measurements can be modeled from the perspective of blind source separation (BSS). Since no comparison between BSS techniques and other signal processing methods has been made, the authors compare a BSS procedure based on higher-order statistics and Widrow's multireference adaptive noise cancelling approach. As a best-case scenario for this latter method, optimal Wiener-Hopf solutions are considered. Both procedures are applied to real multichannel ECG recordings obtained from a pregnant woman. The experimental outcomes demonstrate the more robust performance of the blind technique and, in turn, verify the validity of the BSS model in this important biomedical application.
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paper_title: Fetal electrocardiogram extraction by blind source subspace separation

paper_content:

We propose the emerging technique of independent component analysis, also known as blind source separation, as an interesting tool for the extraction of the antepartum fetal electrocardiogram from multilead cutaneous potential recordings. The technique is illustrated by means of a real-life example.
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paper_title: Multidimensional Independent Component Analysis.

paper_content:

This paper proposes to generalize the notion of independent component analysis (ICA) to the notion of multidimensional independent component analysis (MICA). We start from the ICA or blind source separation (BSS) model and show that it can be uniquely identified provided it is properly parameterized in terms of one-dimensional subspaces. From this standpoint, the BSS/ICA model is generalized to multidimensional components. We discuss how ICA standard algorithms can be adapted to MICA decomposition. The relevance of these ideas is illustrated by a MICA decomposition of ECG signals.
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paper_title: Maximum Likelihood Blind Source Separation: A Context-Sensitive Generalization of ICA

paper_content:

In the square linear blind source separation problem, one must find a linear unmixing operator which can detangle the result xi(t) of mixing n unknown independent sources si(t) through an unknown n × n mixing matrix A(t) of causal linear filters: xi = Σj aij * sj. We cast the problem as one of maximum likelihood density estimation, and in that framework introduce an algorithm that searches for independent components using both temporal and spatial cues. We call the resulting algorithm "Contextual ICA," after the (Bell and Sejnowski 1995) Infomax algorithm, which we show to be a special case of cICA. Because cICA can make use of the temporal structure of its input, it is able separate in a number of situations where standard methods cannot, including sources with low kurtosis, colored Gaussian sources, and sources which have Gaussian histograms.
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paper_title: A fast fixed - point algorithm for independent component analysis

paper_content:

An apparatus for hydrolytic degradation of plastics in which plastic material is deposited into a tubular housing via a feed hopper. An elongated screw shaft has a first section in the form of a high pitch screw thread disposed below the feed hopper to receive and advance the material to a second section. The second section of the screw shaft is in the form of a lower pitch thread for compressing the plastic material and transferring it to a longer, third section in the form of kneading discs, from which material passes through an outlet nozzle section to a cyclone separator where trapped gases and liquid may be withdrawn. The tubular housing is vented upstream of the feed hopper and a water inlet pipe is disposed adjacent to the second section of the screw shaft, downstream of the feed hopper. The outlet nozzle section is provided with pressure measuring and regulating means and a liquid level measuring and regulating device.
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paper_title: The Maternal Abdominal ECG as Input to MICA in the Fetal ECG Extraction Problem

paper_content:

This letter presents a successful system for recovering the fetal electrocardiogram using multidimensional ICA (MICA). MICA requires as many observations as sources. To increase the number of observations, MICA is often applied to data sets that include measurements taken at the mother's thoracic region. However, experiments suggest that the propagation from the maternal heart to the mother's abdomen is not a simple delay, and that approach may fail. Alternatively, our method first estimates the maternal ECG directly from the mother's abdomen. Then, inputs this estimated ECG to MICA. Experiments show superior performance as compared with the traditional approach.
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paper_title: Empirical mode decomposition based ECG enhancement and QRS detection

paper_content:

In this paper an Empirical Mode Decomposition (EMD) based ECG signal enhancement and QRS detection algorithm is proposed. Being a non-invasive measurement, ECG is prone to various high and low frequency noises causing baseline wander and power line interference, which act as a source of error in QRS and other feature extraction. EMD is a fully adaptive signal decomposition technique that generates Intrinsic Mode Functions (IMF) as decomposition output. Here, first baseline wander is corrected by selective reconstruction based slope minimization technique from IMFs and then high frequency noise is removed by eliminating a noisy set of lower order IMFs with a statistical peak correction as high frequency noise elimination is accompanied by peak deformation of sharp characteristic waves. Then a set of IMFs are selected that represents QRS region and a nonlinear transformation is done for QRS enhancement. This improves detection accuracy, which is represented in the result section. Thus in this method a single fold processing of each signal is required unlike other conventional techniques.
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paper_title: ECG signal denoising and baseline wander correction based on the empirical mode decomposition

paper_content:

The electrocardiogram (ECG) is widely used for diagnosis of heart diseases. Good quality ECG are utilized by physicians for interpretation and identification of physiological and pathological phenomena. However, in real situations, ECG recordings are often corrupted by artifacts. Two dominant artifacts present in ECG recordings are: (1) high-frequency noise caused by electromyogram induced noise, power line interferences, or mechanical forces acting on the electrodes; (2) baseline wander (BW) that may be due to respiration or the motion of the patients or the instruments. These artifacts severely limit the utility of recorded ECGs and thus need to be removed for better clinical evaluation. Several methods have been developed for ECG enhancement. In this paper, we propose a new ECG enhancement method based on the recently developed empirical mode decomposition (EMD). The proposed EMD-based method is able to remove both high-frequency noise and BW with minimum signal distortion. The method is validated through experiments on the MIT-BIH databases. Both quantitative and qualitative results are given. The simulations show that the proposed EMD-based method provides very good results for denoising and BW removal.
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paper_title: The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis

paper_content:

A new method for analysing nonlinear and non-stationary data has been developed. The key part of the method is the empirical mode decomposition method with which any complicated data set can be dec...
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paper_title: A novel ECG signal denoising method based on Hilbert-Huang Transform

paper_content:

This paper aims to explore a method about electrocardiogram (ECG) signal denoising based on Hilbert-Huang Transform. The empirical mode decomposition method can decompose the noisy signal into a number of Intrinsic Mode Functions. Energy analysis is conducted on the IMFs to find out the boundary between the noisedominated IMFs and ECG signal dominated IMFs accurately. The most noisy IMFs are denoised by using Donoho soft-threshold denoising method. The denoised high frequency IMFs are added to the low frequency IMFs to reconstruct the original signal. The simulation experiments show that this method is simpler than the wavelet denoising method. It is not necessary to choose wavelet basis or determine the number of layers and the threshold. The proposed method can come close to or achieve the best level of wavelet denoising.
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paper_title: Denoising of ECG signals based on noise reduction algorithms in EMD and wavelet domains

paper_content:

Abstract This paper presents a new ECG denoising approach based on noise reduction algorithms in empirical mode decomposition (EMD) and discrete wavelet transform (DWT) domains. Unlike the conventional EMD based ECG denoising approaches that neglect a number of initial intrinsic mode functions (IMFs) containing the QRS complex as well as noise, we propose to perform windowing in the EMD domain in order to reduce the noise from the initial IMFs instead of discarding them completely thus preserving the QRS complex and yielding a relatively cleaner ECG signal. The signal thus obtained is transformed in the DWT domain, where an adaptive soft thresholding based noise reduction algorithm is employed considering the advantageous properties of the DWT compared to that of the EMD in preserving the energy in the presence of noise and in reconstructing the original ECG signal with a better time resolution. Extensive simulations are carried out using the MIT-BIH arrythmia database and the performance of the proposed method is evaluated in terms of several standard metrics. The simulation results show that the proposed method is able to reduce noise from the noisy ECG signals more accurately and consistently in comparison to some of the stateof-the-art methods.
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paper_title: Wavelet networks

paper_content:

A wavelet network concept, which is based on wavelet transform theory, is proposed as an alternative to feedforward neural networks for approximating arbitrary nonlinear functions. The basic idea is to replace the neurons by 'wavelons', i.e., computing units obtained by cascading an affine transform and a multidimensional wavelet. Then these affine transforms and the synaptic weights must be identified from possibly noise corrupted input/output data. An algorithm of backpropagation type is proposed for wavelet network training, and experimental results are reported. >
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paper_title: ECG signal classification using block-based neural networks

paper_content:

This paper investigates the application of evolvable block-based neural networks (BbNNs) to ECG signal classification. A BbNN consists of a two-dimensional (2-D) array of modular basic blocks that can be easily implemented using reconfigurable digital hardware. BbNNs are evolved for each patient in order to provide personalized health monitoring. A genetic algorithm evolves the internal structure and associated weights of a BbNN using training patterns that consist of morphological and temporal features extracted from the ECG signal of a patient. The remaining part of the ECG record serves as the test signal. The BbNN was tested for ten records collected from different patients provided by the MIT-BIH Arrhythmia database. The evolved BbNNs produced higher than 90% classification accuracies.
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paper_title: ECG signal denoising by Functional Link Artificial Neural Network (FLANN)

paper_content:

Nowadays, Electrocardiogram (ECG) plays an important role in the primary diagnosis, prediction and survival analysis of cardiac diseases. Electrocardiography has had a profound influence on the practice of medicine. The ECG signal contains an important amount of information that can be exploited in different manners. The ECG signal allows for the analysis of anatomic and physiologic aspects of the whole cardiac muscle. Noise reduction in ECG signals is one of the main problems, which appear during analysis of electrical activity of the heart. Such noises are difficult to remove using typical filtering procedures. Efficient analytical tool, which allows increasing signal to noise ratio, is a technique of averaging of cardiac cycles. Effectiveness of this method strictly depends on stable sinus rhythm. Different ECG signals are used to verify the proposed method using MATLAB platform. In this paper, we have proposed Functional Link Artificial Neural Network (FLANN) for the denoising of the ECG signal.
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paper_title: Electrocardiogram (ECG) signal modeling and noise reduction using wavelet neural networks

paper_content:

Electrocardiogram (ECG) signal has been widely used in cardiac pathology to detect heart disease. In this paper, wavelet neural network (WNN) is studied for ECG signal modeling and noise reduction. WNN combines the multi-resolution nature of wavelets and the adaptive learning ability of artificial neural networks, and is trained by a hybrid algorithm that includes the Adaptive Diversity Learning Particle Swarm Optimization (ADLPSO) and the gradient descent optimization. Computer simulation results demonstrate this proposed approach can successfully model the ECG signal and remove high-frequency noise.
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paper_title: An adaptive filtering approach for electrocardiogram (ECG) signal noise reduction using neural networks

paper_content:

Abstract Electrocardiogram (ECG) signals have been widely used in clinical studies to detect heart diseases. However, ECG signals are often contaminated with noise such as baseline drift, electrode motion artifacts, power-line interference, muscle contraction noise, etc. Conventional methods for ECG noise removal do not yield satisfactory results due to the non-stationary nature of the associated noise sources and their spectral overlap with desired ECG signals. In this paper, an adaptive filtering approach based on discrete wavelet transform and artificial neural network is proposed for ECG signal noise reduction. This new approach combines the multi-resolution property of wavelet decomposition and the adaptive learning ability of artificial neural networks, and fits well with ECG signal processing applications. Computer simulation results demonstrate that this proposed approach can successfully remove a wide range of noise with significant improvement on SNR (signal-to-noise ratio).
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paper_title: Some Practical Remarks on Neural Networks Approach to Fetal Cardiotocograms Classification

paper_content:

Cardiotocographic monitoring is a primary biophysical method for assessment of a fetal state based on quantitative analysis of the biophysical signals. Although the computerized fetal monitoring systems have become a standard in clinical centres, the effective methods, which could enable conclusion generation, are still being searched. In the proposed work the attempts have been made to answer some important questions, which occurred during application of neural network for classification of the fetal state as being normal or abnormal. These questions are particularly important for medical applications and concern the influence of data set organization, inputs representation and the network's architecture. The networks of MLP and RBF types were developed and tested using 50 trials, with randomly mixed data contents in learning, validating and testing subsets. Additionally, the influence of numerical and categorical representation of the input quantitative parameters describing fetal cardiotocograms on the efficiency of the learning process was tested.
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paper_title: Genetic algorithm and wavelet hybrid scheme for ECG signal denoising

paper_content:

This paper introduces an effective hybrid scheme for the denoising of electrocardiogram (ECG) signals corrupted by non-stationary noises using genetic algorithm (GA) and wavelet transform (WT). We first applied a wavelet denoising in noise reduction of multi-channel high resolution ECG signals. In particular, the influence of the selection of wavelet function and the choice of decomposition level on efficiency of denoising process was considered. Selection of a suitable wavelet denoising parameters is critical for the success of ECG signal filtration in wavelet domain. Therefore, in our noise elimination method the genetic algorithm has been used to select the optimal wavelet denoising parameters which lead to maximize the filtration performance. The efficiency performance of our scheme is evaluated using percentage root mean square difference (PRD) and signal to noise ratio (SNR). The experimental results show that the introduced hybrid scheme using GA has obtain better performance than the other reported wavelet thresholding algorithms as well as the quality of the denoising ECG signal is more suitable for the clinical diagnosis.
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paper_title: ECG Signal Denoising Using Wavelet Thresholding Techniques in Human Stress Assessment

paper_content:

In recent years, Electrocardiogram (ECG) plays an imperative role in heart disease diagnostics, Human Computer Interface (HCI), stress and emotional states assessment, etc. In general, ECG signals affected by noises such as baseline wandering, power line interference, electromagnetic interference, and high frequency noises during data acquisition. In order to retain the ECG signal morphology, several researches have adopted using different preprocessing methods. In this work, the stroop color word test based mental stress inducement have done and ECG signals are acquired from 10 female subjects in the age range of 20 years to 25 years. We have considered the Discrete Wavelet Transform (DWT) based wavelet denoising have incorporated using different thresholding techniques to remove three major sources of noises from the acquired ECG signals namely, power line interference, baseline wandering, and high frequency noises. Three wavelet functions ("db4", "coif5" and "sym7") and four different thresholding methods are used to denoise the noise in ECG signals. The experimental result shows the significant reduction of above considered noises and it retains the ECG signal morphology effectively. Four different performance measures were considered to select the appropriate wavelet function and thresholding rule for efficient noise removal methods such as, Signal to Interference Ratio (SIR), noise power, Percentage Root Mean Square Difference (PRD) and finally periodogramof Power Spectral Density (PSD). The experimental result shows the "coif5" wavelet andrigrsurethresholding rule is optimal for unknown Signal to Noise Ratio (SNR) in the real time ECG signals.
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paper_title: Interference cancellation in EMG signal Using ANFIS

paper_content:

In this paper, Adaptive Neuro Fuzzy Inference System (ANFIS) is proposed to cancel the electrocardiogram (ECG) interference in electromyogram (EMG) signal. Conventional filtering techniques are not suitable due to an overlap in spectral content of the desired signal (EMG) and the interference. Comparison of results is made between the proposed technique and the other artificial intelligence techniques like Back Propagation Network (BPN), and Cascade Correlation Network (CCN). The performance evaluation of the proposed technique is done in terms of signal to noise ratio, mean square error, and convergence time. It shows that ANFIS successfully cancel the interference in EMG signal.
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paper_title: Power line interference filtering on surface electromyography based on the stationary wavelet packet transform

paper_content:

Power line interference is one of the main problems in surface electromyogram signals (EMG) analysis. In this work, a new method based on the stationary wavelet packet transform is proposed to estimate and remove this kind of noise from EMG data records. The performance has been quantitatively evaluated with synthetic noisy signals, obtaining good results independently from the signal to noise ratio (SNR). For the analyzed cases, the obtained results show that the correlation coefficient is around 0.99, the energy respecting to the pure EMG signal is 98-104%, the SNR is between 16.64 and 20.40dB and the mean absolute error (MAE) is in the range of -69.02 and -65.31dB. It has been also applied on 18 real EMG signals, evaluating the percentage of energy respecting to the noisy signals. The proposed method adjusts the reduction level to the amplitude of each harmonic present in the analyzed noisy signals (synthetic and real), reducing the harmonics with no alteration of the desired signal.
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paper_title: Identification of optimal wavelet-based algorithm for removal of power line interferences in ECG signals

paper_content:

Identification of optimal denoising algorithm for ECG signals using DWT is described. The parameters are determined by comparing different types of wavelet functions, decomposition levels and threshold selection methods. The algorithm is used to improve the SNR of the ECG contaminated by disturbances like power line interferences, to present a clean signal for accurate auto diagnosis.
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paper_title: Empirical mode decomposition based ECG enhancement and QRS detection

paper_content:

In this paper an Empirical Mode Decomposition (EMD) based ECG signal enhancement and QRS detection algorithm is proposed. Being a non-invasive measurement, ECG is prone to various high and low frequency noises causing baseline wander and power line interference, which act as a source of error in QRS and other feature extraction. EMD is a fully adaptive signal decomposition technique that generates Intrinsic Mode Functions (IMF) as decomposition output. Here, first baseline wander is corrected by selective reconstruction based slope minimization technique from IMFs and then high frequency noise is removed by eliminating a noisy set of lower order IMFs with a statistical peak correction as high frequency noise elimination is accompanied by peak deformation of sharp characteristic waves. Then a set of IMFs are selected that represents QRS region and a nonlinear transformation is done for QRS enhancement. This improves detection accuracy, which is represented in the result section. Thus in this method a single fold processing of each signal is required unlike other conventional techniques.
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paper_title: Arrhythmia ECG Noise Reduction by Ensemble Empirical Mode Decomposition

paper_content:

A novel noise filtering algorithm based on ensemble empirical mode decomposition (EEMD) is proposed to remove artifacts in electrocardiogram (ECG) traces. Three noise patterns with different power—50 Hz, EMG, and base line wander – were embedded into simulated and real ECG signals. Traditional IIR filter, Wiener filter, empirical mode decomposition (EMD) and EEMD were used to compare filtering performance. Mean square error between clean and filtered ECGs was used as filtering performance indexes. Results showed that high noise reduction is the major advantage of the EEMD based filter, especially on arrhythmia ECGs.
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paper_title: Removal of power-line interference from the ECG: a review of the subtraction procedure

paper_content:

BackgroundModern biomedical amplifiers have a very high common mode rejection ratio. Nevertheless, recordings are often contaminated by residual power-line interference. Traditional analogue and digital filters are known to suppress ECG components near to the power-line frequency. Different types of digital notch filters are widely used despite their inherent contradiction: tolerable signal distortion needs a narrow frequency band, which leads to ineffective filtering in cases of larger frequency deviation of the interference. Adaptive filtering introduces unacceptable transient response time, especially after steep and large QRS complexes. Other available techniques such as Fourier transform do not work in real time. The subtraction procedure is found to cope better with this problem.MethodThe subtraction procedure was developed some two decades ago, and almost totally eliminates power-line interference from the ECG signal. This procedure does not affect the signal frequency components around the interfering frequency. Digital filtering is applied on linear segments of the signal to remove the interference components. These interference components are stored and further subtracted from the signal wherever non-linear segments are encountered.ResultsModifications of the subtraction procedure have been used in thousands of ECG instruments and computer-aided systems. Other work has extended this procedure to almost all possible cases of sampling rate and interference frequency variation. Improved structure of the on-line procedure has worked successfully regardless of the multiplicity between the sampling rate and the interference frequency. Such flexibility is due to the use of specific filter modules.ConclusionThe subtraction procedure has largely proved advantageous over other methods for power-line interference cancellation in ECG signals.
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paper_title: Integrating the ECG power-line interference removal methods with rule-based system.

paper_content:

The power-line frequency interference in electrocardiographic signals is eliminated to enhance the signal characteristics for diagnosis. The power-line frequency normally varies +/- 1.5 Hz from its standard value of 50 Hz. In the present work, the performances of the linear FIR filter, Wave digital filter (WDF) and adaptive filter for the power-line frequency variations from 48.5 to 51.5 Hz in steps of 0.5 Hz are studied. The advantage of the LMS adaptive filter in the removal of power-line frequency interference even if the frequency of interference varies by +/- 1.5 Hz from its normal value of 50 Hz over other fixed frequency filters is very well justified. A novel method of integrating rule-based system approach with linear FIR filter and also with Wave digital filter are proposed. The performances of Rule-based FIR filter and Rule-based Wave digital filter are compared with the LMS adaptive filter.
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paper_title: Characterization and elimination of AC noise in electrocardiograms: a comparison of digital filtering methods

paper_content:

Abstract Diverse digital methods have been advanced previously to remove power line (AC) interference in the ECG. Representative notch filters, adaptive filters and a globally derived filter are surveyed in this study; their performances are compared on artificial signals as well as actual ECGs. The ECGs, recorded at four European medical centers, are from the Common Standards in Electrocardiography (CSE) ECG tape library. AC interference in these ECGs is shown to exhibit two qualities especially relevant to filter design: considerable deviations from a nominal 50 Hz frequency and substantial noise at higher harmonics. Some criteria and useful quantitative measures are suggested to evaluate AC digital filters.
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paper_title: A dynamical model for generating synthetic electrocardiogram signals

paper_content:

A dynamical model based on three coupled ordinary differential equations is introduced which is capable of generating realistic synthetic electrocardiogram (ECG) signals. The operator can specify the mean and standard deviation of the heart rate, the morphology of the PQRST cycle, and the power spectrum of the RR tachogram. In particular, both respiratory sinus arrhythmia at the high frequencies (HFs) and Mayer waves at the low frequencies (LFs) together with the LF/HF ratio are incorporated in the model. Much of the beat-to-beat variation in morphology and timing of the human ECG, including QT dispersion and R-peak amplitude modulation are shown to result. This model may be employed to assess biomedical signal processing techniques which are used to compute clinical statistics from the ECG.
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paper_title: Online Digital Filter and QRS Detector Applicable in Low Resource ECG Monitoring Systems

paper_content:

The present work describes fast computation methods for real-time digital filtration and QRS detection, both applicable in autonomous personal ECG systems for long-term monitoring. Since such devices work under considerable artifacts of intensive body and electrode movements, the input filtering should provide high-quality ECG signals supporting the accurate ECG interpretation. In this respect, we propose a combined high-pass and power-line interference rejection filter, introducing the simple principle of averaging of samples with a predefined distance between them. In our implementation (sampling frequency of 250 Hz), we applied averaging over 17 samples distanced by 10 samples (Filter10x17), thus realizing a comb filter with a zero at 50 Hz and high-pass cut-off at 1.1 Hz. Filter10x17 affords very fast filtering procedure at the price of minimal computing resources. Another benefit concerns the small ECG distortions introduced by the filter, providing its powerful application in the preprocessing module of diagnostic systems analyzing the ECG morphology. Filter10x17 does not attenuate the QRS amplitude, or introduce significant ST-segment elevation/depression. The filter output produces a constant error, leading to uniform shifting of the entire P-QRS-T segment toward about 5% of the R-peak amplitude. Tests with standardized ECG signals proved that Filter10x17 is capable to remove very strong baseline wanderings, and to fully suppress 50 Hz interferences. By changing the number of the averaged samples and the distance between them, a filter design with different cut-off and zero frequency could be easily achieved. The real-time QRS detector is designed with simplified computations over single channel, low-resolution ECGs. It relies on simple evaluations of amplitudes and slopes, including history of their mean values estimated over the preceding beats, smart adjustable thresholds, as well as linear logical rules for identification of the R-peaks in real-time. The performance of the QRS detector was tested with internationally recognized ECG databases (AHA, MIT-BIH, European ST-T database), showing mean sensitivity of 99.65% and positive predictive value of 99.57%. The performance of the presented QRS detector can be highly rated, comparable and even better than other published real-time QRS detectors. Examples representing some typical unfavorable conditions in real ECGs, illustrate the common operation of Filter10x17 and the QRS detector.
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paper_title: Denoising of ECG signals based on noise reduction algorithms in EMD and wavelet domains

paper_content:

Abstract This paper presents a new ECG denoising approach based on noise reduction algorithms in empirical mode decomposition (EMD) and discrete wavelet transform (DWT) domains. Unlike the conventional EMD based ECG denoising approaches that neglect a number of initial intrinsic mode functions (IMFs) containing the QRS complex as well as noise, we propose to perform windowing in the EMD domain in order to reduce the noise from the initial IMFs instead of discarding them completely thus preserving the QRS complex and yielding a relatively cleaner ECG signal. The signal thus obtained is transformed in the DWT domain, where an adaptive soft thresholding based noise reduction algorithm is employed considering the advantageous properties of the DWT compared to that of the EMD in preserving the energy in the presence of noise and in reconstructing the original ECG signal with a better time resolution. Extensive simulations are carried out using the MIT-BIH arrythmia database and the performance of the proposed method is evaluated in terms of several standard metrics. The simulation results show that the proposed method is able to reduce noise from the noisy ECG signals more accurately and consistently in comparison to some of the stateof-the-art methods.
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paper_title: Suppressing harmonic powerline interference using multiple-notch filtering methods with improved transient behavior

paper_content:

Abstract In signal processing it is often required to have multiple-notch filters which simultaneously possess a very selective magnitude response and a transient response of short duration. Multiple-notch filters are usually used to remove the powerline hum and its harmonics. It is known, that sharper notches are obtained by either using more coefficients in FIR filters, or by placing the pole closer to the unit circle in IIR filters. However, increasing the filter selectivity also increases the duration of the transient process in the filter after the action of the excitation. This paper presents and compares two methods for suppressing the transient response in multiple-notch filters. As an example, these methods have been used to eliminate the powerline noise from the ECG signal. Both filtering techniques are characterized by improved transient behavior compared to the traditional multiple-notch filters. In the first part of the paper a concept of digital IIR multiple-notch filters whose pole radius changes with time is proposed. Owing to a temporary change in the value of the pole radius, the transient can be considerably reduced. In the second part of this review the technique which uses the vector projection to find better initial values for time-invariant multiple-notch filter is presented. Simulations verifying the effectiveness of the proposed IIR multiple-notch filter with time-varying pole radius and the filter with non-zero initial conditions are presented and compared to the performance of the traditional time-invariant filter using an ECG signal with unwanted fixed-frequency harmonic interferences as a study case.
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paper_title: ENSEMBLE EMPIRICAL MODE DECOMPOSITION: A NOISE-ASSISTED DATA ANALYSIS METHOD

paper_content:

A new Ensemble Empirical Mode Decomposition (EEMD) is presented. This new approach consists of sifting an ensemble of white noise-added signal (data) and treats the mean as the final true result. Finite, not infinitesimal, amplitude white noise is necessary to force the ensemble to exhaust all possible solutions in the sifting process, thus making the different scale signals to collate in the proper intrinsic mode functions (IMF) dictated by the dyadic filter banks. As EEMD is a time–space analysis method, the added white noise is averaged out with sufficient number of trials; the only persistent part that survives the averaging process is the component of the signal (original data), which is then treated as the true and more physical meaningful answer. The effect of the added white noise is to provide a uniform reference frame in the time–frequency space; therefore, the added noise collates the portion of the signal of comparable scale in one IMF. With this ensemble mean, one can separate scales naturall...
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Title: Fetal ECG Extraction from Abdominal Signals: A Review on Suppression of Fundamental Power Line Interference Component and Its Harmonics

Section 1: Introduction
Description 1: This section introduces the importance of fetal heart rate (fHR) and fetal electrocardiogram (fECG) analyses in monitoring fetal health, and the challenges posed by power line interference (PLI).

Section 2: PLI Cancellation Using Digital Fixed Notch Filters
Description 2: This section discusses the use of digital notch filters to cancel narrow band interferences, their limitations, and specific design considerations for suppressing PLI.

Section 3: Adaptive Filtering in PLI Cancellation
Description 3: This section explains the use of adaptive filters which adjust their parameters to track changes in PLI frequency, highlighting their advantages and practical drawbacks.

Section 4: Blind Source Separation Applied in PLI Suppression
Description 4: This section covers the application of blind source separation techniques to statistically separate the fECG signal from the PLI and other noise components.

Section 5: Hilbert Huang Transform Applied in PLI Reduction
Description 5: This section introduces the Hilbert Huang Transform (HHT) method, its application in nonstationary signal analysis, and its specific approach to identifying and cancelling PLI components.

Section 6: PLI Cancellation by Applying Neural Networks
Description 6: This section discusses the application of neural networks for PLI suppression in fECG signals, detailing a specific neural network architecture and its training methodology.

Section 7: PLI Reduction by Applying the Wavelet Transform
Description 7: This section reviews the use of wavelet transforms for denoising ECG signals and the process of identifying and subtracting PLI using discrete stationary wavelet packet transform.

Section 8: Data Simulation and Performance Measurements
Description 8: This section describes the generation of simulated data for evaluating PLI suppression algorithms and the performance indices used to measure their effectiveness.

Section 9: Results
Description 9: This section presents the results obtained from applying various PLI suppression algorithms on simulated data, comparing their performance across different scenarios.

Section 10: Discussion
Description 10: This section discusses the implications of the obtained results, detailing the performance of each algorithm, its limitations, and suitability for real applications.

Section 11: Conclusions
Description 11: This section summarizes the review, highlighting the most effective PLI suppression methods and suggesting directions for future research.