Journal of perinatal medicine vol:14 issue:6 pages:421-33
The detection of a fetal electrocardiogram (FECG) is described to be a so-called inverse problem. A geometric interpretation of such a problem is presented. It can be solved by determining the weights to be used in one or more weighted sums of measurement signals. A novel method is presented to determine these weights. Theoretical and experimental evidence is given that this method has the following attractive properties. Application of the method results in one or more FECG signals, free of maternal ECG (MECG) which are at the same time maximal with respect to noise. It is shown that one FECG signal does not always suffice to describe the observed electrical heart activity in a set of cutaneous electrodes, equivalently to the adult ECG (see figure 7). It is explained and experimentally verified that the application of three thoracic signals is useful to guarantee the suppression of the MECG. The positions of the abdominal electrodes then determine the obtained FECG to noise ratio, and will have no influence on the degree of MECG suppression (see figure 6). It is expected that a total of about eight measurement signals are sufficient in most cases. The method is simple to apply by medical personnel, and after a transient of about 1 s the signals with the mentioned properties are obtained (see figure 5). Further on, the weights are allowed to change in order to adapt automatically to sudden changes in the measurement signal properties (see figure 6). These may occur e. g. due to fetal movement. Application of the method requires no human interpretation or decision in order to obtain the claimed properties.