| Co-Investigator(Kenkyū-buntansha) |
TSUKADA Keiji Hitachi, Ltd., Central Reseach Laboratory, Senior Researcher, 中央研究所, 主任研究員
SHIGEMITSU Sadahiko Institute of Clinical Medicine, Assistant Professor, 臨床医学系, 講師 (20235526)
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| Research Abstract |
To assess the functional development of fetal central nervous system, we first analyzed heart rate variability in the fetus based on the data set of RR intervals obtained by fetal megnetocardiography (fMCG), fMCG was recorded in uncomplicated fetuses with the gestational age of 20-40 weeks, and power spectral analysis was applied to calculate the power of the low frequency band (LF), high frequency band (HF) and LF/HF ratio. Consequently, it was demonstrated that the power of LF (sympathetic activity) increases significantly with the gestational age although that of HF (parasympathetic activity) remained unchanged during the period. The LF/HF ratio also increases in proportion with the gestational age, indicating sympathetic dominance in later gestation. Thus, .fMCG is recognized as useful methodology to evaluate fetal autonomic nervous system or fetal well-being, as the detection rate of R waves and the time resolution are very high.
Then, we attempted to measure auditory evoked magnet
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ic fields of the fetal - brain. The detection of fetal megnetoencephalogram (fMEG) has been considered very hard because the magnitude of fMEG signals is much weaker than that of fMlCG, almost at the level of units of 10^<-14> Tesla, and because signal averaging technique is difficult to apply due to non-cyclic nature of the signals. To improve the success, rate of recording fMEG, we refined the sensors of the SQUID system and realized spatial resolution of <10 fT/√<Hz>. fMEG was recorded over the site of fetal skull on maternal abdomen under stimulation with acoustic pulses (frequency, 0.5 or 1KHz ; magnitude, 70-100 dB ; width, 50 msec) with a stimulus frequency of 0.5 Hz for 8 min. The signals obtained were averaged triggered by the acoustic pulse. With this methodology, a peak of MEG signal was detected at 120 msec after the pulse in neonates immediately after birth, and two peaks were detected at 120 and 220 msec after the pulse in infants. However, no apparent fMEG peaks were determined for fetuses even in full term. We concluded that further improvement of sensitivity of the SQUID system, auditory stimulation and recording methods, and post processing of the'data would be required to assess the functional development or maturation of the fetal brain using fMEG. Less
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