Research of fetal circulation dynamics by means of cross-correlation of the fetal heart rates between twin fetuses

在双胎同步胎心监护仪上进行无负荷试验时，常可观察到两胎在相同时间间隔内的CTG波形相似。我们通过互相关函数研究了这种心率模式的相似性。在我们大学医院，用双胞胎心脏监护仪（TOITU，MT-430）对双胞胎胎儿进行了NST，并通过A/D转换器将监护仪的输出胎儿心率收集到个人计算机中。转换器的采样时间为0.2秒。NST进行约25分钟。对13例胎龄25 ~ 38周的55个胎心率波形进行分析，计算相关函数，以相关系数的最大值作为峰值和延迟时间。在一个活跃期，由CTG计算得到的互相关函数有一个峰值，该峰值在大多数道上大于0.20，其平均值和标准差分别为0.433和0.164。峰值的平均延迟时间为12.4秒。在静止相，大多数迹线没有互相关函数的典型峰值，峰值的平均值和S. D为0.191和0.215。单绒毛膜双胎与双绒毛膜双胎的相关函数无特征性差异，提示双胎胎心率曲线的相似性主要来源于活跃期的加速度。两个胎儿的加速度平均时间差约为12秒，这表明心率对触觉刺激的反应存在差异。

When non-stress test (NST) is performed for twins by a simultaneous fetal heart rate monitor, we often observe a similar pattern in the traces of CTGs of both fetuses during same time interval. We investigated this similarity of the heart rates patterns by means of a crosscorrelation function.In our university hospital, the NST was performed for twin fetuses with a cardiotocomonitor for twins (TOITU, MT-430), and the output fetal heart rate from the monitor was collected to a personal computer through an A/D converter. Sampling time of the converter was 0.2 sec. and the NST was performed for about 25 minutes. Crosscorrelation function was calculated from the data of the fetal heart rates, and a maximum value of the crosscorrelation coefficient was measured as a peak value and a delay time.We analyzed 55 traces of 13 cases of which gestational age were from 25 to 38 weeks. In an active phase we were able to find a peak of crosscorrelation function calculated from the CTG.Value of the peak was greater than 0.20 in the most traces, and its mean and S.D.were 0.433 and 0.164 respectively. The average delay time of the peak was 12.4 seconds. In a resting phase most traces have no typical peak of the crosscorrelation function and mean and S.D.of the peak value were 0.191 and 0.215. There were no obvious relationship between the crosscorrelation and gestational age, and no characteristic difference between the crosscorrelation functions of mono-chorionic and di-chorionic twins.It was suggested that the similarity of the fetal heart rate trace between twin fetuses was derived chiefly from the acceleration in the active phase. The average time difference of the acceleration in both fetuses was about 12 seconds, and it was suggestive of difference in the heart rate response to the tactile stimulation.