1Department of Obstetrics and Gynecology, Iwate Medical University School of Medicine, 2Tohoku University Biomedical Engineering Research Organization, Division of Telecommunication and Information Technology, 3Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Tohoku University Graduate School of Medicine
“Raw Doppler signals”, cardiac Doppler signals obtained from the precordia, can cover the entire heart. These signals are extremely complicated and comprise many components: motion associated with the cardiac valves, cardiac muscles, and blood flow in the cardiac chambers, among others. It thus seems possible that a system capable of processing these signals could providee useful information on cardiac structure and function. We analyzed cardiac Doppler signals using the wavelet transform in order to evaluate fetal cardiac function and used continuous wavelet analysis to examine the time-frequency distribution of cardiac Doppler signals obtained from a fetal heart rate monitoring system. The time-frequency distribution showed that phase changed with cardiac cycle and developed a generic pattern showing bifurcation in phase transition in low-frequency areas in the scalogram. Clarity of bifurcation of phase transition in low-frequency areas improved with increase in gestational age. In cases of fetal cardiac dysfunction, beat-to-beat spectral independency in the time-frequency distribution of cardiac Doppler signals decreased remarkably. The pattern resembled a spectral pattern recognized in less mature fetuses. Engineers can use vibration and spectral handling of sound signals to monitor the condition of the fetal heart. This method promises to provide a new way to evaluate cardiac function by applying signal analysis to the diagnosis of fetal conditions.