On-line fetal heart rate monitor by phonocardiography

The beat-to-beat fetal heart rate variability can be evaluated using the fetal phonocardiogram (fPCG) as a part of a well-being evaluation procedure. In previous works, we have developed and tested an off-line algorithm to generate cardiotachograms (CTGs) by processing fPCGs. This method has showed its confidence to generate reliable CTGs, especially when maximums of cardiac sounds (S1 and S2) are used. Now we are interested to change our off-line processing scheme into a first on-line fetal heart rate monitor version. This monitor was developed with a LabView-Matlab program, it acquires and processes the fPCGs displaying, almost on-line, the CTGs generated by S1 and S2. It also storages information and provides the possibility to manually correct CTGs. For testing the monitor, off-line time references from five testing signals were calculated, and compared against monitor time references. This comparison showed good results on detecting on-line time references and intervals. The system really works as a monitor, it acquires and processes signals during 20 minutes at least, and its CTGs do not differ from the off-line CTGs for more than 2 ms. The system is now ready to include an adaptive filter that improves its performance with fPCGs.