A. Matonia

Quantitative analysis of contraction patterns in electrical activity signal of pregnant uterus as an alternative to mechanical approach

Monitoring of uterine contraction activity is an important diagnostic tool used during both pregnancy and labour. The strain the pregnant uterus exerts on the maternal abdomen is measured via external tocography. However, limitation of this approach has caused the development of another technique-electrohysterography--which is based on the recording of electrical uterine activity. A computer-aided system is presented, which allows the recording of electrohysterographic signals from the maternal abdomen and their on-line analysis both in time and frequency domains. As a research material, we acquired 108 traces during a 24 h period before labour from a group of patients between 37 and 40 weeks of gestation. The comparison study between electrohysterography and tocography was carried out thanks to the possibility of simultaneous recording of mechanical and electrical uterine activities. The obtained results show that both methods demonstrate high agreement in relation to the number of contractions recognized as being consistent. However, their agreement in relation to the quantitative description of recognized patterns has appeared to be unacceptable to consider these methods as fully alternative. The appropriate way of further development of electrohysterography seems to be spectral analysis. Several spectral parameters describing electrophysiological properties of uterine muscle can be obtained by the use of electrohysterographic signals.

Determination of fetal heart rate from abdominal signals: evaluation of beat-to-beat accuracy in relation to the direct fetal electrocardiogram

Abstract The main aim of our work was to assess the reliability of indirect abdominal electrocardiography as an alternative to the commonly used Doppler ultrasound monitoring technique. As a reference method, we used direct fetal electrocardiography. Direct and abdominal signals were acquired simultaneously, using dedicated instrumentation. The developed method of maternal signal suppression as well as fetal QRS complexes detection was presented. Recordings were collected during established labors, each consisted of four signals from the maternal abdomen and the reference signal acquired directly from the fetal head. After assessing the performance of the QRS detector, the accuracy of fetal heart rate measurement was evaluated. Additionally, to reduce the influence of inaccurately detected R-waves, some validation rules were proposed. The obtained results revealed that the indirect method is able to provide an accuracy sufficient for a reliable assessment of fetal heart rate variability. However, the method is very sensitive to recording conditions, influencing the quality of signals. Our investigations confirmed that abdominal electrocardiography, even in its current stage of development, offers an accuracy equal to or higher than an ultrasound method, at the same time providing some additional features.

Computerized analysis of fetal heart rate signals as the predictor of neonatal acidemia

Cardiotocography is the primary method for biophysical assessment of fetal state, which is mainly based on the recording and analysis of fetal heart rate (FHR) signal. Computerized systems for fetal monitoring provide a quantitative analysis of FHR signals, however the effective methods of qualitative assessment that could support the process of medical diagnosis are still needed. The measurements of hydronium ions concentration (pH) in neonatal cord blood are an objective indicator of the fetal outcome. Improper pH level is a symptom of acidemia being the result of fetal hypoxia. The paper proposes a two-step analysis of fetal heart rate recordings that allows for effective prediction of the acidemia risk. The first step consists in fuzzy classification of FHR signals. Fuzzy inference corresponds to the clinical interpretation of signals based on the FIGO guidelines. The goal of inference is to eliminate recordings indicating the fetal wellbeing from the further classification process. In the second step, the remained recordings are nonlinearly classified using multilayer perceptron and Lagrangian Support Vector Machines (LSVM). The proposed procedures are evaluated using data collected with computerized fetal surveillance system. The assessment performance is evaluated with the number of correct classifications (CC) and quality index (QI) defined as the geometric mean of sensitivity and specificity. The highest CC=92.0% and QI=88.2% were achieved for the Weighted Fuzzy Scoring System combined with the LSVM algorithm. The obtained results confirm the efficacy of the proposed methods of computerized analysis of FHR signals in the evaluation of the risk of neonatal acidemia.

Towards noise immune detection of fetal QRS complexes

The noninvasive fetal electrocardiography is a source of more precise information on the fetal heart activity than the measurements based on Doppler ultrasound signals. However, the clinical diagnostic applications of this technique are limited by difficulty with successful detection of small amplitude fetal QRS complexes. In this study, we investigate the influence of different stages of fetal signals processing on the detection performance. The main propositions of the paper are: application of normalized matched filtering to fetal QRS complexes enhancement and a new approach to the final detection of the complexes. Compared to the classical detectors, the proposed new one allows a significant increase of the detection performance for signals of very different quality.

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.

Timing events in Doppler ultrasound signal of fetal heart activity

Among various methods of monitoring fetal heart activity a Doppler ultrasound technique is the most often used. Complexity and variability of Doppler signal make difficult the precise measurement of timing dependences defining individual phases of cardiac cycle. Aim of the work was to carry out detailed comparative analysis of Doppler echo coming from movement of two different objects within fetal heart: valve and wall. Joint time frequency analysis were applied. Fetal monitor performed a role of input device in our measurement station based on LabView environment. Doppler signal was acquired from analog outputs with a help of dedicated data acquisition card. Average recording time in a group of 15 patients was 20 minutes. Analysis comprised determination and comparison of spectrograms and power density spectrums corresponding to individual phases of cardiac cycle.

Application of spatio-temporal filtering to fetal electrocardiogram enhancement

In this paper we propose a new structure of the instrumentation for electrocardiographic fetal monitoring. We apply a single-channel approach to maternal electrocardiogram suppression in the recorded four abdominal bioelectric signals. Then we exploit spatial and temporal properties of the extracted four-channel fetal electrocardiogram to construct a new channel with higher signal-to-noise ratio. Finally, we perform detection of fetal QRS complexes. The proposed approach is investigated with the help of the constructed database of the maternal abdominal signals. During the detection tests, the spatio-temporal filtering allowed us to decrease significantly the number of the detection errors of different detectors applied. Moreover, we present visually that even if the fetal QRS complexes are buried in noise, the spatio-temporal filtering can produce the signal with the discernible ones.

The Maternal ECG Suppression Algorithm for Efficient Extraction of the Fetal ECG from Abdominal Signal

At present, noninvasive recording of abdominal fetal electrocardiogram and analysis of the fetal heart rate variability seems to be the most promising method to detect the fetal hypoxia. The main problem is to obtain a good quality fetal ECG, which is strongly distorted by maternal component of dominating energy. The paper presents the new method of maternal electrocardiogram recognition and suppression relying on determination of template maternal PQRST complex and its subtraction during consecutive maternal cardiac cycles. The efficiency of the developed method was evaluated and related to three other selected methods for maternal ECG suppression using dedicated coefficients created for this comparison

A new approach to cardiotocographic fetal monitoring based on analysis of bioelectrical signals

A new approach alternative to cardiotocographic conventional fetal monitoring is presented. It relies upon analysis of bioelectrical signals recorded from maternal abdominal wall. Due to strong interferences present in abdominal signal advanced methods of signal processing have been developed to extract fetal electrocardiogram and uterine electrical activity signal. The described system allows replacement of more expensive cardiotocographic instrumentation based on ultrasound Doppler method and ensures the higher diagnostic capacity at the same time.

Instrumentation for Fetal Cardiac Performance Analysis During the Antepartum Period

Cardiotocography as a simultaneous recording of fetal heart rate (FHR) and uterine contraction activity is a basic method for evaluation of fetal condition. Continuous variability of the fetal heart rate is an indirect sign of adequate oxygenation of a fetus. Unfortunately, the reverse case is not always true, signs suggesting pathological changes can also appear in recording when the fetal is not at risk. The cardiotocography shall then be recognized as a more screening than diagnostic method. It will be interesting to develop a noninvasive method being complementary to routine cardiotocography. This method should allow the adequate prediction of a bad clinical outcome when the test is abnormal. The paper presents the system that makes possible cardiotocograms analysis in parallel with the assessment of additional parameters determined from comparison of mechanical and electrical fetal heart activity signals. The studies are aimed at development of set of parameters that are high correlated with fetal outcome