During the past decade a variety of intrapartum fetal monitors have been constructed that process the entire fetal electrocardiogram (FECG), obtained via a scalp electrode. They therefore differ from conventional monitors in aiming to extract relevant timing and magnitude information from the morphology of the FECG rather than simply the RR interval and hence heart rate. An intrapartum monitor such as this has been successfully developed by ourselves. This paper describes the early results obtained whilst attempting to extend this form of monitoring forward into the antenatal period. In order to achieve this the FECG must be acquired via surface electrodes placed on the maternal abdomen, which yields a signal containing the FECG amidst a number of noise sources. Our investigations into the feasibility of "antenatal abdominal FECG analysis" have been on two fronts. The first has been to produce a bedside monitor similar in function to our intrapartum device, whilst the second has been to address the possibility of performing such monitoring in ambulant subjects. At present the antenatal bedside monitor has successfully extracted and processed the FECG in approximately 75% of the cases studied, with subjects ranging from 20 weeks through to term having been monitored. We also have demonstrated the feasibility of the long term monitoring of maternal and fetal heart rate using a portable instrument.
The aim of this study was to demonstrate the acquisition of both the fetal magnetocardiogram (FMCG) and fetal electrocardiogram (FECG) from the abdomen of the same subject. This contrasts with previous reported studies which have generally recorded one or other of these signals but not the two together. Both signals were successfully recorded and averaged to produce a typical complex, thus allowing their direct comparison.
A PC based instrument has been developed to extract and analyse the fetal electrocardiogram (FECG) obtained via surface electrodes from the maternal abdomen. This is capable of running either off-line, using recorded signals, or on-line for use by a clinician during routine antenatal examinations. The system produces maternal and fetal beat-to-beat heart rate infonnation, coherently averaged maternal and FECG complexes and an analysis of the FECG complex showing such parameters as PR duration and QRS width.Results have been obtained from over 50 recordings from volunteers of gestational ages between 20 and 39 weeb. IntroductionThe extraction and subsequent analysis of the fetal electrocardiogram (FECG) from the maternal abdomen can potentially provide the clinician with an indication of fetal status. Currently such FECG assessment can be performed during labour, using signals obtained from a scalp electrode [l]. The translation of this technique into the antepartum period using signals obtained from the maternal abdomen is therefore a natural development of this work.Over the past few decades many attempts have been made at achieving this, with most work concentrating on the extraction of the FECG [2-51. However as yet no clinical diagnostic use is made of the FECG.This paper firstly provides a description of the instrumentation and procedure used to obtain the raw signals, followed by an overview of the Pc based system developed to perform real-time FECG extraction and analysis. 0216-6541f93 $3.00 0 1993 IEEE 2. FECG Signal AcquisitionSignals are obtained from the matemal thorax and abdomen via a specially designed four channel isolation amplifier which has a flat hquency response between 0.5 and 100 Hz and 3dB points at 0.05 and 250 Hz. This extended low frequency response together with the accompanying flat phase response minimises distortion of the low frequency components in the FECG such as the P and T waves which could hinder precise clinical diagnosis.As well as being processed on-line the signals obtained are also recorded on a E A C R-7 1 data recorder for future analysis. Abdominal signals are taken in both vertical and horizontal directions, with electrodes spaced about 25cm apart and equidistant with the umbilicus. These abdominal signals consist of matemal and fetal ECG complexes (typical amplitudes of lOOpV and 20pV respectively) as well as a variety of noise sources (discussed below). In order to make these signal magnitudes suitable for digitisation, amplification by a factor of 10, OOO is required. Digitisation is performed at a sampling rate of 500Hz with 16 bit resolution.The electrodes used are the wet gel disposable (silverhilver chloride) type. The skin is first cleaned with alcohol saturated cotton wool to remove grease, dirt and dead skin cells thus decreasing the skin electrode impedance.Problems associated with obtaining suitable traces include large baseline drift (which can cause amplifier saturation), abdominal muscle noise which can swamp the ECG signals and 50Hz interference. These...
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