Masahito Yoshizawa

Assessment of Fetal Autonomic Nervous System Activity by Fetal Magnetocardiography

Aim To clarify the significance of heart rate variability for the evaluation of an autonomic nervous system (ANS) in the normal fetus using fetal magnetocardiography (FMCG). Methods Subjects consisted of normal pregnancy (n = 35) at 28-39 weeks gestation. FMCG was recorded using 64-channel magnetocardiography (MCG) in a magnetically shielded room. The QRS interval was derived from signal-averaged MCG. The R-R interval variability induced by an R-wave trigger was eventually adopted to calculate for time-domain and frequency domain analysis. The power spectrum in the frequency domain was derived from frequency-field components using the maximum entropy method of fetal heart rate variability. Based on frequency analysis, the ranges of the LF and HF domains were defined as 0.01-0.15 and 0.15-0.4 Hz, respectively. We defined a coefficient of variance (CVRR) as an index of parasympathetic activity, and defined a low frequency/high frequency (LF/HF) ratio as a sympathetic activity. Results The value of CVRR in the normal pregnancy group displayed a slight increasing trend with gestational age (y = 1.77 + 0.10x; r = 0.32). In contrast, the LF/HF ratio in the normal pregnancy group clearly increased over the gestational period (one-way ANOVA: P = 0.003). Conclusions Analyses based on the time and frequency domains of heart rate variability using FMCG enable an evaluation of fetal ANS activity. Sympathetic nervous activity increased with gestational age in the normal pregnancy group.

MgB2 SQUID for Magnetocardiography

The discovery of the superconductivity at a transition temperature (TC) of 39 K in magnesium diboride (MgB2) has attracted much attention from many researchers for scientific as well as technical reasons [1]. Compared with Cu-based superconductors (cuprates), MgB2 has lower anisotropy and larger coherence length, in addition to high Tc [2]. These characteristics of MgB2 give rise to new applications for superconductor devices that can operate in the temperature range between 20 and 30 K; examples of such devices are Josephson junctions and integrated circuits. This temperature range can be easily achieved by using economical and compact cryocoolers or liquid hydrogen. The use of cryocoolers may transform the superconductor from being specialized and advanced technology into common usage in consumer devices. In the future, hydrogen gas may be widely used for carbon-free power generation such as in fuel cells. Liquid hydrogen would be available for these purposes, and may be utilized for the cooling of low-temperature devices. In addition, MgB2 is considered to be a clean superconducting material, using neither toxic nor rare earth elements.