A design of fetal monitoring system based on the time-frequency analysis of fetal heart beat fluctuation using wavelet transform

我们研究了胎儿自主神经系统的非线性控制机制是否会在不同的胎儿状态下发生变化。从正常、低氧血症和酸血症胎儿中检测到8000或更多胎心搏动。采用高精度自相关法测定胎儿心脏多普勒信号间期，得到胎儿心率波动时间序列。应用小波变换时频分析方法研究了胎儿心率频率低频成分中时间波动幅度的分布。样条4被用作母小波函数。从妊娠17周开始观察到伽马分布。该伽马分布的参数uppermance的值约为1.6，并且无论孕龄或一天中的时间如何都保持恒定。结果表明，胎儿心率波动的γ分布时间序列呈非线性结构，当胎儿出现酸血症时，心率波动值为0.77，低氧血症时为1.51，正常时为1.54。该技术可能为胎儿监护提供一种新的定量指标，以诊断胎儿酸血症。

We examined whether the non-linear control mechanism of the fetal autonomic nervous system would change in various fetal states. 8000 or more fetal heart beats were detected from normal, hypoxemic and acidemic fetuses. Fetal heart Doppler signal intervals were determined in a high-precision autocorrelation method and a time series of fetal heart rate fluctuation was obtained. The distribution of the amplitude of temporal fluctuation in the low frequency component of fetal heart rate frequency was studied using a method of time-frequency analysis called wavelet transform. Spline 4 was used as the mother wavelet function. A gamma distribution was observed from 17 weeks of gestation onward. The value of the parameter upsilon of this gamma distribution was approximately 1.6 and remained constant regardless of the gestation age or the time of the day. The value of upsilon decreased significantly to 0.77 when the fetus developed acidemia, and was 1.51 in hypoxemia and 1.54 in a normal condition.This study elucidates a non-linear structure of the time series of heart rate fluctuation of the gamma distribution in human fetus. This technique may provide a new quantitative index of fetal monitoring to diagnose fetal acidemia.