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Electrohysterographic volume conductor modeling

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Bayesian approach to patient-tailored vectorcardiography

For assessment of specific cardiac pathologies, vectorcardiography is generally considered superior with respect to electrocardiography. Existing vectorcardiography methods operate by calculating the vectorcardiogram (VCG) as a fixed linear combination of ECG signals. These methods, with the inverse Dower matrix method the current standard, are therefore not flexible with respect to different body compositions and geometries. Hence, they cannot be applied with accuracy on patients that do not conform to the fixed standard. Typical examples of such patients are obese patients or fetuses. For the latter category, when recording the fetal ECG from the maternal abdomen the distance of the fetal heart with respect to the electrodes is unknown. Consequently, also the signal attenuation/transformation per electrode is not known. In this paper, a Bayesian method is developed that estimates the VCG and, to some extent, also the signal attenuation in multichannel ECG recordings from either the adult 12-lead ECG or the maternal abdomen. This is done by determining for which VCG and signal attenuation the joint probability over both these variables is maximal given the observed ECG signals. The underlying joint probability distribution is determined by assuming the ECG signals to originate from scaled VCG projections and additive noise. With this method, a VCG, tailored to each specific patient, is determined. The method is compared to the inverse Dower matrix method by applying both methods on standard 12-lead ECG recordings and evaluating the performance in predicting ECG signals from the determined VCG. In addition, to model nonstandard patients, the 12-lead ECG signals are randomly scaled and, once more, the performance in predicting ECG signals from the VCG is compared between both methods. Finally, both methods are also compared on fetal ECG signals that are obtained from the maternal abdomen. For patients conforming to the standard, both methods perform similarly, with the developed method performing marginally better. For scaled ECG signals and fetal ECG signals, the developed method significantly outperforms the inverse Dower matrix method

Fetal movement quantification by fetal vectrocardiography: a preliminary study.

Fetal movement is a valuable source of information to monitor the neurological development of the fetus and assess fetal health. Currently, fetal movement can be assessed by the mother or detected by analysis of ultrasound images. Long-term monitoring of movement is complicated with both these methods as maternal self-assessment has a relatively poor sensitivity and specificity and automatic analysis of ultrasound images is not available. Moreover, ultrasound transducers transmit energy into the body, potentially endangering fetal health. In this paper, an alternative method for fetal movement monitoring is presented. This method operates by estimating and analyzing the fetal vectorcardiogram (VCG) from non-invasive recordings on the maternal abdomen. The determined fetal movement is compared with that assessed from a simultaneously performed ultrasound recording; the results of the presented method are consistent with the ultrasound images. In addition, the presented method enables quantification of the rotation angles by means of analysis of the rotation matrix between consecutive fetal VCGs, providing a tool for long-term monitoring of fetal movement with increased specificity

Electrohysterographic conduction velocity estimation

Monitoring and analysis of the fetal-heart and the uterine-muscle activity, referred to as electrohysterogram (EHG), is essential to permit timely treatment during pregnancy. While remarkable progress is reported for monitoring of the fetal cardiac activity, the EHG measurement and interpretation remains challenging, and limited knowledge is available on the underlying physiological processes. In particular, little attention has been paid to the analysis of the EHG propagation, whose characteristics might indicate the presence of coordinated uterine contractions leading to intrauterine pressure increase. Therefore, this study focuses for the first time on the noninvasive estimation of the conduction velocity of EHG action potentials by means of multichannel EHG recording and surface high-density electrodes. A maximum likelihood algorithm, initially proposed for skeletal-muscle electromyography, is modified for the required EHG analysis. The use of clustering and weighting is introduced to deal with poor signal similarity between different channels. The presented methods were evaluated by specific simulations, proving the combination of weighting and clustering to be the most accurate method. A preliminary EHG measurement during labor confirmed the feasibility of the method. An extensive clinical validation will however be necessary to optimize the method and assess the relevance of the EHG conduction velocity for pregnancy monitoring

A simulation model to study maternal hyperoxygenation during labor

To investigate the effect of maternal hyperoxygenation on fetal oxygenation and fetal heart rate decelerations during labor, using a simulation model. Design Use of a mathematical model that simulates feto–maternal hemodynamics and oxygenation, designed in Matlab R2012a. Setting Clinical and engineering departments in the Netherlands. Methods We simulated variable and late fetal heart rate decelerations, caused by uterine contractions with a different contraction interval. We continuously recorded oxygen pressure in different feto–placental compartments and fetal heart rate, during maternal normoxia and during hyperoxygenation with 100% oxygen. Main outcome measures Changes in oxygen pressure in the intervillous space, umbilical vein and arteries, fetal cerebral and microcirculation as well as fetal heart rate deceleration depth and duration. Results Maternal hyperoxygenation leads to an increase in fetal oxygenation: in the presence of variable decelerations, oxygen pressure in the intervillous space increased 9–10 mmHg and in the cerebral circulation 1–2 mmHg, depending on the contraction interval. In addition, fetal heart rate deceleration depth decreased from 45 to 20 beats per minute. In the presence of late decelerations, oxygen pressure in the intervillous space increased 7–10 mmHg and in the cerebral circulation 1–2 mmHg, depending on the contraction interval. The fetus benefited more from maternal hyperoxygenation when contraction intervals were longer. Conclusions According to the simulation model, maternal hyperoxygenation leads to an increase in fetal oxygenation, especially in the presence of variable decelerations. In addition, in the presence of variable decelerations, maternal hyperoxygenation leads to amelioration of the fetal heart rate pattern

In-vitro volumeberekening met behulp van driedimensionale echoscopie

Driedimensionale echoscopie neemt toe in populariteit.De klinische relevantie van driedimensionale echoscopie voor de verloskunde is echter niet bewezen. Wij veronderstellen dat de mogelijkheid van volumemetingen een meerwaarde zal opleveren voor de klinische praktijk. De standaard gebruikte handmatige methode is bewerkelijk en afhankelijk van de ervaring van de onderzoeker. Het is gelukt een semigeautomatiseerde methode voor volumeberekeningen te ontwikkelen. Deze methode is reproduceerbaar en lijkt betrouwbaar. In dit artikel worden de resultaten besproken van een pilotstudy