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- Title
Variability analysis of fetal heart rate signals as obtained from abdominal electrocardiographic recordings.
- Authors
Cerutti, Sergio; Baselli, Giuseppe; Civardi, Silvia; Ferrazzi, Enrico; Marconi, Anna Maria; Pagani, Massimo; Pardi, Giorgio
- Abstract
The present paper introduces an original method of digital signal processing for an automatic analysis of non-invasive abdominal ECG recordings on pregnant women starting from the 25th week of gestation. The procedure has been implemented on a DEC-VAX 750 digital computer at the Department of Electrical Engineering, Polytechnic of Milano and the signals are recorded at the Department of Obstetrics and Gynecology "L. Mangiagalli", University of Milano, Italy. The experimental results presented in here are still preliminary as only few cases have been considered up to now (about 20) and the goal of the paper is mainly focused on the algorithmic aspects of the whole procedure implemented in the computer and on the approach of heart rate variability (HRV) signal analysis both in the mother and in the fetus. Abdominal EGG lead processing is illustrated starting from the step of maternal (M) and fetal (F) QRS recognitions through linear digital filtering (derivative and low-pass FIR filter, Weber-Cappellini window) and weighted averaging techniques synchronized with maternal QRS's. Figure 1 a shows the original abdominal lead; figure 1 b the filtered signal for MQRS recognitions; figure 2 a the template of maternal cardiac cycle as obtained after the averaging operation synchronized with the instants of MQRS occurrence. The subtraction of the template results in the abdominal lead shown in figure 1 c in which the contribution of MECG is practically entirely reduced even in the case of MQRS and FQRS overlapping. An important result is shown in figure 2b where the entire fetal cardiac cycle is obtained after a further averaging of the signal shown in figure 1 c, with a synchronization on fetal QRS instants of occurrence. Fetal P wave and QRS complex are clearly visible. Further analysis is then made of the HRV signals (both maternal and fetal) obtained through low pass filtered event series (LPFES) in correspondence with each QRS occurrence (figure 3). Traditional analysis of HRV signal in the form of mean value and variance are introduced together with the more advanced technique of power spectral density (PSD) estimation, carried out via autoregressive (AR) modelling of the discrete-time samples of HRV signals (figure 4) over a time interval of about 2 min. The power spectra indicate the two main rhythms which characterize HRV signals. The first one lies around a frequency of 0.1 Hz (also called the 10s rhythm) and the second one corresponds to respiration rate. Measurements carried out in adult humans connect these rhythms to the behaviour of the autonomic nervous system (ANS) which controls heart rate through sympathetic and parasympathetic efferents [1, 15]. Several important observations may be deduced from the analysis of the data shown in figure 5 and figure 6. The autospectrum of fetal HRV indicates that here the basic 10s rhythm exists as well, thus indicating the effect of ANS in mediating sympathetic and parasympathetic drives. Another rhythmic component in the depolarization of the fetal sino-atrial node is also evident (smaller than the previous one) which is synchronous with maternal respiration frequency, thus confirming a complex interaction between a mechanical influence of maternal breathing and a neural reflex in the fetus. A deeper analysis in the cross spectrum (amplitude, phase and coherence spectra) may provide quantitative information about the intimate relationships between the two variability signals. Applications are foreseen in the physiological studies of the evolution of cardiovascular and neural mechanisms of the fetus, linked to the normal activity of the mother. Clinical implications are also obvious: monitoring of important vital functions of the riskful fetuses starting from an early period of the pregnancy and control of the relevant parameters of mother and fetus during drug delivery or in case of severe pathologies.
- Publication
Journal of Perinatal Medicine, 1986, Vol 14, Issue 6, p445
- ISSN
0300-5577
- Publication type
Article