Center for Research in Health Technologies and Information Systems-CINTESIS, Faculty of Medicine, University of Porto, Al. Prof. Hernâni Monteiro, 4200-319 Porto, Portugal.
Med Biol Eng Comput. 2013 Jun;51(6):665-76. doi: 10.1007/s11517-013-1036-7. Epub 2013 Jan 24.
Evaluation of foetal heart rate (FHR) variability is an essential part of foetal monitoring, but a precise quantification of this parameter depends on the quality of the signal. In this study, we compared real FHR beat-to-beat signals with 4 Hz sampling provided by commercial foetal monitors on linear and nonlinear indices and analysed their clinical implications. Simultaneous acquisition of beat-to-beat signals and their 4 Hz sampling rate counterparts was performed using a scalp electrode, during the last hour of labour in 21 fetuses born with an umbilical artery blood (UAB) pH ≥ 7.20 and 6 born with an UAB pH < 7.20. For each case, the first and last 10 min segments were analysed, using time and frequency domain linear, and nonlinear FHR indices, namely mean FHR, low frequency, high frequency, approximate, sample and multiscale entropy. Significant differences in variability indices were found between beat-to-beat and 4 Hz sampled signals, with a lesser effect seen with 2 Hz sampling. These differences did not affect physiological changes observed during labour progression, such as decreased entropy and linear time domain indices, and increased frequency domain indices. However, significant differences were found in the discrimination between fetuses born with different UAB pHs, with beat-to-beat sampling providing better results in linear indices and 4 Hz sampling better results in entropy indices. In conclusion, different FHR sampling frequencies can significantly affect the quantification of variability indices. This needs to be taken into account in the interpretation of FHR variability and in the development of new equipment.
胎儿心率（FHR）变异性的评估是胎儿监测的重要组成部分，但该参数的精确量化取决于信号的质量。在本研究中，我们比较了真实的 FHR 逐拍信号和商业胎儿监护仪以 4 Hz 采样率提供的线性和非线性指数，并分析了它们的临床意义。使用头皮电极在 21 名出生时脐动脉血（UAB）pH 值≥7.20 的胎儿和 6 名出生时 UAB pH 值<7.20 的胎儿分娩的最后 1 小时内同时采集逐拍信号及其 4 Hz 采样率对应信号。对于每个病例，使用时间和频率域线性和非线性 FHR 指数，即平均 FHR、低频、高频、近似、样本和多尺度熵，分析了前 10 分钟和最后 10 分钟的片段。在逐拍和 4 Hz 采样信号之间，发现变异性指数存在显著差异，而 2 Hz 采样的影响较小。这些差异并没有影响分娩过程中观察到的生理变化，如熵和线性时域指数降低，以及频域指数增加。然而，在区分出生时 UAB pH 值不同的胎儿方面，逐拍采样在线性指数方面提供了更好的结果，而 4 Hz 采样在熵指数方面提供了更好的结果，这两种方法存在显著差异。总之，不同的 FHR 采样频率会显著影响变异性指数的定量。在解释 FHR 变异性和开发新设备时，需要考虑这一点。
