Foetal heart rate power spectrum response to uterine contraction

Cardiotocography is the most diffused prenatal diagnostic technique in clinical routine. The simultaneous recording of foetal heart rate (FHR) and uterine contractions (UC) provides useful information about foetal well-being during pregnancy and labour. However, foetal electronic monitoring interpretation still lacks reproducibility and objectivity. New methods of interpretation and new parameters can further support physicians’ decisions. Besides common time-domain analysis, study of the variability of FHR can potentially reveal autonomic nervous system activity of the foetus. In particular, it is clinically relevant to investigate foetal reactions to UC to diagnose foetal distress early. Uterine contraction being a strong stimulus for the foetus and its autonomic nervous system, it is worth exploring the FHR variability response. This study aims to analyse modifications of the power spectrum of FHR variability corresponding to UC. Cardiotocographic signal tracts corresponding to 127 UC relative to 30 healthy foetuses were analysed. Results mainly show a general, statistically significant (t test, p<0.01) power increase of the FHR variability in the LF 0.03–0.2 Hz and HF 0.2–1 in correspondence of the contraction with respect to a reference tract set before contraction onset. Time evolution of the power within these bands was computed by means of time-varying spectral estimation to concisely show the FHR response along a uterine contraction. A synchronised grand average of these responses was also computed to verify repeatability, using the contraction apex as time reference. Such modifications of the foetal HRV that follow a contraction can be a sign of ANS reaction and, therefore, additional, objective information about foetal reactivity during labour.     

Comparison of short term variability indexes in cardiotocographic foetal monitoring

Concise indexes related to variability of foetal heart rate (FHR) are usually utilised for foetal monitoring; they enrich information provided by cardiotocography (CTG). Most attention is paid to the short term variability (STV), which relates to activity and reaction of autonomic nervous control of foetal heart. There is not a unique method to compute short term variability of the FHR but different formulas have been proposed and are employed in clinical and scientific environments: this leads to different evaluations and makes difficult comparative studies. Nine short term variability indexes: Arduini, Dalton, Organ, Sonicaid 8000, Van Geijn, Yeh, Zugaib a modified version of Arduini index and Standard Deviation were considered and compared to test their robustness in CTG applications. A large set of synthetic foetal heart rate series with known features were used to compare indexes performances. Different amounts of variability, mean foetal heart rate, storage rates, baseline variations were considered. The different indexes were in particular tested for their capability to recognise short term heart rate variability variation, their dependence on heart rate signal storage rate (as those provided by commercial cardiotocographic devices), on mean value of the foetal heart rate and on modifications of the floatingline, such in case of accelerations or decelerations.Concise statistical parameters relative to indexes scores were presented in comparative tables.Results indicate that although the indexes are able to recognise STV variation, they show substantial differences in magnitude and some in sensibility. Results depend on the frequency used to acquire and store FHR data (depending on devices); in general, the lower is data rate the more degraded are the results. Furthermore, results differently depend on FHR mean, some for their intrinsic definition; differences arise also in correspondences of accelerations and decelerations. Our results demonstrate that only indexes which refer directly to differences in FHR values, such as Organ and SD indexes, not show dependence on FHR mean.The use of the Standard Deviation index may provide efficient information while showing independence from the considered variables.Indexes performance in case of real cardiotocographic signals were also presented as examples.     

The information content of Doppler ultrasound signals from the fetal heart

Knowledge of the content of Doppler ultrasound signals from the fetal heart is essential if the performance of fetal heart rate (FHR) monitors based upon this technology is to be improved. For this reason instrumentation was constructed to enable the simultaneous collection of Doppler audio signals and the transabdominal fetal ECG (for signal registration), with a total of 22 recordings being made with an average length of around 20 minutes. These data demonstrate the transient nature of the Doppler audio data with wide variations in the signal content observable on a beat-to-beat basis. Short-time Fourier analysis enabled the content of the Doppler signals to be linked to six cardiac events, four valve and two wall motions, with higher frequency components being associated with the latter. This differing frequency content together with information regarding the direction of movement that can be discerned from Doppler signals provided a potential means of discriminating between these six events (which are unlikely to all contribute to the Doppler signal within the same cardiac cycle). Analysis of 100 records showed that wall contractions generate the most prominent signals, with atrial contraction recognisable in all records and ventricular wall contraction in 95% (although its amplitude is only around 30% of that of the atrial signal). Valve motion, with amplitudes between 15 and 25% that of the atrial wall signal, were visible in 75% of records. These results suggest means by which the six events that contribute to the Doppler signal may be distinguished, providing information that should enable an improvement in the current performance of Doppler ultrasound-based FHR monitors.     

Complete foetal ECG morphology recording by synchronised adaptive filtration

Present noninvasively measured indices of foetal stress are indirect and not sufficient. Foetal electrocardiography (FECG) is a potential noninvasive measurement of the foetus wellbeing which has been little utilised because of the difficulties of measuring it. The development of time-sequenced adaptive filters which are synchronised to the QRS complex by the use of Doppler echocardiography allowed the recording of relatively noise-free FECG. The paper describes the use of this technique for obtaining the complete complex of the FECG. Several sets of time-sequenced adaptive filters are combined to allow a multilead abdominal recording to produce a measurement system which rejects maternal ECG and enhances the FECG. Five subjects have been analysed, and their FECGs have been accurately reproduced with minimal changes of the filters' parameters.     

Comparison of correlation and modulus difference processing algorithms for the determination of foetal heart rate from ultrasonic Doppler signals

Microprocessor-based correlation processing is now widely used for the estimation of foetal heart rate from ultrasonic Doppler signals. The paper describes a technique having a, similar performance, to correlation but which will run three times faster on a microprocessor without an onboard hardware multiplier. This speed improvement results from replacing each multiplication operation of the correlation algorithm with a subtraction and a modulus operation. The algorithm, is thus referred to as the modulus difference algorithm. Typical waveforms are presented illustrating the responses of the two processors to continuous wave Doppler foetal heart signals for both wide (50 Hz) and narrow (4 Hz) preprocessor bandwidths. A quantitative comparison is given of the performance of the two methods in estimating the period of a synthetic signal with additive white Gaussian noise. This simulation represents the wideband preprocessor case. A theoretical derivation of the outputs for the narrowband preprocessor case is given, and actual outputs are shown for comparison. A tutorial approach is adopted throughout the paper.     

Comparison of SVD methods to extract the foetal electrocardiogram from cutaneous electrode signals

The paper presents and compares three methods making use of the singular value decomposition (SVD) of a matrix to extract the foetal electrocardiogram (FECG) from cutaneously recorded electrode signals. The first method constructs a set of orthogonal foetal signals (the so-called principal foetal signals) from the recordings, but needs electrode positions far from the foetal heart, in addition to the abdominal electrodes that pick up a mixture of maternal and foetal electrocardiogram. An online adaptive algorithm has been developed such that a real-time implementation becomes feasible. The second method is a new online approach to a technique presented by van Oosterom. Although this method has some important drawbacks and is suboptimal as far as foetal signal-to-noise ratio is concerned. it is still very useful when only a foetal trigger is required, as the signal obtained is not a complete FECG, Finally, a third method is proposed, based on the generalised SVD and interpreted with the new concept of oriented signal-to-signal ratio. An online version is also presented for this method and some results are shown.     

Improvement in Doppler ultrasound human foetal heart rate records by signal correlation

An improved method for the determination of foetal heart rate from Doppler ultrasound signals is described and evaluated. It determines the most probable pulse interval from the recurrence times of multiple echoes generated by each cardiac pulse. The method, when optimised, is shown to offer an improvement over current systems, especially in reduced signal loss.     

一种基于自相关和平均模差算法的胎儿心率提取方法

目的 胎儿心率是判断孕期胎儿健康状况的一项重要指标,使用超声多普勒测量胎心率是常用的无创方法.其中,自相关算法是常用的测量胎心率的算法,但是其抗噪性差,容易出错.方法 本文提出一种基于自相关与平均标准模差相结合的新算法,先通过自相关函数突显其周期性,然后用累计平均标准模差函数提取准确周期,最后通过使用该算法处理模拟器数据和临床数据,验证其精确度和抗噪性.结果 相比滑动窗算法,基于自相关和平均标准模差的算法具有更高的精确度和抗噪性.结论 改进后的算法可以有效计算出胎心率值.     

Passive fetal monitoring by adaptive wavelet denoising method

Fetal Heart Rate (FHR) monitoring is one of the most important fetal well being tests. Existing FHR monitoring methods are based on Doppler ultrasound technique, which has several disadvantages. Passive fetal monitoring by phonocardiography is an appropriate alternative; however, its implementation is a challenging task due to low energy of fetal heart sounds and multiple interference signals presence. In this paper, an advanced signal processing method for passive fetal monitoring based on adaptive wavelet denoising is presented. The method's performance is compared with Doppler ultrasound monitor. The results show 94-97.5% accuracy, including highly disturbed cases.     

Improved Doppler ultrasonic monitoring of the foetal heart rate

The Doppler ultrasonic technique for the monitoring of the foetus has been available for well over a decade. It offers a noninvasive assessment of the condition of the foetus and has therefore become an important antenatal technique. However, the foetal heart rate information obtained by this technique is considered to be less precise than that obtained from the foetal e.c.g. The waveforms recorded by the Doppler ultrasonic method are complex and variable and this often leads to difficulty in identifying a reliable and regular measuring point within these waveforms from which to calculate the heart rate. This has resulted in a cautious acceptance of ultrasonically determined foetal heart-rate records. This paper does not dispute the difficulties of interpreting such rate information, but outlines a pair of algorithms for processing and presenting a more accurate and reliable indication of the foetal heart rate determined from the Doppler ultrasonic method. These algorithms calculate a two second average rate from only those intervals which have been determined to be ‘valid’, based on the criterion that they should be within ±10% of the most previous valid interval.     

新一代胎儿监护仪的研制

胎儿心电监护是预防围产期胎死的一项重要措施，作者介绍了一种基于８０９８单片机系统，利用匹配滤波技术进行信号处理以及采用大屏幕液晶显示的新一代胎儿心电心率监护仪，它具有体积小，重量轻，耗电量低，检测算法简单可靠的特点，经临床实验，成功地检出了胎儿心电波及胎儿心率。     

Assessment of autonomic function in the late term fetus: The effects of sex and state

Researchers have reported associations between fetal sex and heart rate (FHR) and heart rate variability (FHRV) but rarely in the context of fetal behavioral sleep state. We examined differences in measures of fetal autonomic function by sex and sleep state. Fetal abdominal ECG monitoring technology was used to measure FHR and two measures of FHRV—standard deviation of FHR (SD) and beat-to-beat variability (RMSSD). FHR and movement patterns were also recorded with standard Doppler ultrasound monitor technology employed to code sleep states. Data were collected from 82 healthy fetuses ranging from 36 to 39 weeks gestation. A one-way MANOVA showed that FHR was significantly lower and SD was significantly higher for males than females. Independent samples t tests found that these sex differences were only in the active sleep state. There were no significant differences in RMSSD by sex. Repeated measures MANOVA for a subset that exhibited more than one state (N = 22) showed that SD was significantly different by state. RMSSD showed a marginally significant sleep state difference. In conclusion, fetal sex differences in HR and HRV may indicate more mature autonomic functioning in near-term males than females and fetal sleep state can influence abdominal fECG derived measures of FHR and FHRV.     

Prenatal predictors of infant temperament

Emerging data suggest that prenatal factors influence children's temperament. In 50 dyads, we examined fetal heart rate (FHR) activity and women's antenatal psychiatric illness as predictors of infant temperament at 4 months (response to novelty and the Infant Behavior Checklist). FHR change during maternal challenge was positively associated with observed infant motor reactivity to novelty (p = .02). The odds of being classified as high versus low motor among fetuses who had an increase in FHR during maternal stress was 11 times those who had a decrease in FHR (p = .0006). Antenatal psychiatric diagnosis was associated with an almost fourfold greater odds of having a high cry reactivity classification (p = .03). There also were modest associations between baseline FHR and maternal reports of infant temperament and between observed temperament and that based on mothers' reports. All of the infant results were found independent of the influence of women's postnatal anxiety. These data indicate that physiological markers of individual differences in infant temperament are identifiable in the fetal period, and possibly shaped by the prenatal environment.     

Fetal heart rate monitoring based on independent component analysis

In this paper, an algorithm based on independent component analysis (ICA) for extracting the fetal heart rate (FHR) from maternal abdominal electrodes is presented. Three abdominal ECG channels are used to extract the FHR in three steps: first preprocessing procedures such as DC cancellation and low-pass filtering are applied to remove noise. Then the algorithm for multiple unknown source extraction (AMUSE) algorithm is fed to extract the sources from the observation signals include fetal ECG (FECG). Finally, FHR is extracted from FECG. The method is shown to be capable of completely revealing FECG R-peaks from observation leads even with a SNR=-200dB using semi-synthetic data.     

基于coif5小波的多普勒胎心音信号提取算法的研究

胎心率监护是围产期胎儿监护的关键技术指标，超声多普勒测量胎心率是最常用的无创方法。由于胎心多普勒信号具有信噪比低、非平稳的随机性特点，提出基于coif5小波，结合双重阈值方法的胎心音信号提取算法。实验表明，该算法有效地解决了由于胎心率加倍、减半所引起的胎心率曲线翻转问题，提高了多普勒胎心音信号提取的准确性。     

The influence of coincidence of fetal and maternal QRS complexes on fetal heart rate reliability

Bioelectrical fetal heart activity being recorded from maternal abdominal surface contains more information than mechanical heart activity measurement based on the Doppler ultrasound signals. However, it requires extraction of fetal electrocardiogram from abdominal signals where the maternal electrocardiogram is dominant. The simplest technique for maternal component suppression is a blanking procedure, which relies upon the replacement of maternal QRS complexes by isoline values. Although, in case of coincidence of fetal and maternal QRS complexes, it causes a loss of information on fetal heart activity. Its influence on determination of fetal heart rate and the variability analysis depends on the sensitivity of the heart-beat detector used. The sensitivity is defined as an ability to detect the incomplete fetal QRS complex. The aim of this work was to evaluate the influence of the maternal electrocardiogram suppression method used on the reliability of FHR signal being calculated.     

Classification of foetal heart rate sequences based on fractal features

Visual inspection of foetal heart rate (FHR) sequences is an important means of foetal well-being evaluation. The application of fractal features for classifying physiologically relevant FHR sequence patterns is reported. The use of fractal features is motivated by the difficulties exhibited by traditional classification schemes to discriminate some classes of FHR sequence and by the recognition that this type of signal exhibits features on different scales of observation, just as fractal signals do. To characterise the signals by fractal features, two approaches are taken. The first models the FHR sequences as temporal fractals. The second uses techniques from the chaos-theory field and aims to model the attractor based on FHR sequences. The fractal features determined by both approaches are used to design a Bayesian classification scheme. Classification results for three classes are presented; they are quite satisfactory and illustrate the importance of this type of methodology.     

Simultaneity of foetal heart rate acceleration and foetal trunk movement determined by foetal magnetocardiogram actocardiography

We describe a new method of actocardiography, foetal magnetocardiogram (fMCG) actocardiography, which is based on the high sensitivity of the fMCG to foetal trunk movements. We demonstrate the efficacy of the method by applying it to assess the simultaneity of onset of foetal heart rate (FHR) acceleration and foetal trunk movement. The analysis was restricted to events for which the onset of FHR accelerations and foetal movements could be determined accurately, i.e. when FHR was stable and near the average quiescent level just prior to the acceleration. We found that FHR accelerations coincided with or preceded foetal movements nearly all the time. This supports the hypothesis of coordinated control of FHR accelerations and foetal movements more strongly than prior studies, based on other techniques. We also found that beat-to-beat FHR variability often decreased at or near the start of FHR accelerations and that this occurrence was an accurate marker of foetal movement onset, even when foetal movement onset lagged FHR accelerations.     

Antepartum cardiotocography: a study of fetal reactivity in frequency domain

Cardiotocography (CTG) is the most widely used diagnostic technique in clinical practice to monitor fetal health. Cardiotocographic recording also permits to assess maturation of the fetal autonomous nervous system (ANS): fetal heart rate (FHR) modifications may reveal ANS’ reactions to stimuli. To assess fetal reactivity, physicians evaluate specific clinical CTG parameters, generally, by means of visual inspection, thus depending on observer's expertise, with lack of reproducibility. Still nowadays, there is a very high intra- and inter-observer variation in the assessment of FHR patterns. More objective methods for CTG interpretation are of crucial importance. For adults, frequency analysis of heart rate variability (HRV) is a non-invasive and powerful method to investigate ANS activity. This frequency analysis can also be a valid support for a better knowledge of fetal ANS functional state and reactions. Indeed, fetal HRV is a good indicator of fetal well-being in non-stress conditions. Fetal reactivity is a very important CTG characteristic used to diagnose fetal distress, but its interpretation is still uncertain. The aim of this study is to characterise fetal reactivity proposing new fetal HRV frequency parameters to support a more exhaustive CTG analysis.     

Portable directional ultrasonic Doppler blood velocimeter for ambulatory use

The design of a portable directional Doppler velocimeter and of purposebuilt probes intended for monitoring blood flow in femorodistal bypass grafts in ambulatory patients are described. The design is based on a continuous-wave Doppler technique with quadrature demodulation. The Doppler unit was interfaced to a ‘personal-stereo’ recorder to store the Doppler signals. The advantages and the limitations of recording flow in ambulatory patients are discussed. Examples of blood flow data collected from femorodistal bypass grafts are given.