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Abstract
The most commonly used method of fetal monitoring is based on heart activity analysis. Computer-aided fetal monitoring system enables extraction of clinically important information hidden for visual interpretation—the instantaneous fetal heart rate (FHR) variability. Today’s fetal monitors are based on monitoring of mechanical activity of the fetal heart by means of Doppler ultrasound technique. The FHR is determined using autocorrelation methods, and thus it has a form of evenly spaced—every 250 ms—instantaneous measurements, where some of which are incorrect or duplicate. The parameters describing a beat-to-beat FHR variability calculated from such a signal show significant errors. The aim of our research was to develop new analysis methods that will both improve an accuracy of the FHR determination and provide FHR representation as time series of events. The study was carried out on simultaneously recorded (during labor) Doppler ultrasound signal and the reference direct fetal electrocardiogram Two subranges of Doppler bandwidths were separated to describe heart wall movements and valve motions. After reduction of signal complexity by determining the Doppler ultrasound envelope, the signal was analyzed to determine the FHR. The autocorrelation method supported by a trapezoidal prediction function was used. In the final stage, two different methods were developed to provide signal representation as time series of events: the first using correction of duplicate measurements and the second based on segmentation of instantaneous periodicity measurements. Thus, it ensured the mean heart interval measurement error of only 1.35 ms. In a case of beat-to-beat variability assessment the errors ranged from −1.9% to −10.1%. Comparing the obtained values to other published results clearly confirms that the new methods provides a higher accuracy of an interval measurement and a better reliability of the FHR variability estimation.
Highlights
Cardiotocography is a crucial part of modern perinatal medicine, which enables to monitor and assess a fetal condition during pregnancy and labor
The highest errors |∆Ti | relate to the band associated with heart wall movements and the main reason is the more blurred impulse shape in the envelope, which leads to less evident peak in autocorrelation function (AF)
Using a popular fetal monitor based on the Doppler ultrasound technique, it is possible to analyze the fetal heart rate signal only in a classical approach, which consists in determining the FHR baseline for recognizing the patterns of tachycardia/bradycardia or acceleration/deceleration
Summary
Cardiotocography is a crucial part of modern perinatal medicine, which enables to monitor and assess a fetal condition during pregnancy and labor. It involves recording a fetal heart rate (FHR) signal against uterine contractile activity and fetal movements [1,2,3,4,5]. Sensors 2020, 20, 4079 or decelerations are defined as episodes of increasing or slowing of the heart rate. Another activity feature is an instantaneous variability, represented by two components: short-term variability (STV)
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