Variations of multifractal structure in the fetal heartbeats

Several procedures for evaluating fetal well-being are in clinical use. The cardiotocograph is mostly used as a non-invasive procedure to measure fetal well-being in clinical settings. The cardiotocograph displays the fetal heartbeat counts that vibrate. This variation has been classified into 2 categories. We investigated this variation by a novel method, in which we analyzed the change of structure of the attractors in the phase spaces according to the time course. We adopted the global spectrum, which means the distribution of fractal dimensions, for that structure. In this procedure, we discovered a new variation in which the cycle is much longer than the 2 types of known variabilities. Although loud noises such as white noises with a magnitude 1/4 times as large as the standard deviation of the original data were added to the original data, the variations were still detected. The variation is very difficult to detect by Fourier or wavelet transformation, however, because it changes very slowly. Through this new way of analyzing the vibration phenomena, we obtained a new perspective on the biological information available.