Schwilden Helmut, Jeleazcov Christian
Department of Anaesthesia, Friedrich-Alexander-Universität Erlangen--Nürnberg, Krankenhausstr. 12, D-91054 Erlangen, Germany.
J Clin Monit Comput. 2002 Dec;17(7-8):449-57. doi: 10.1023/a:1026284321451.
Bispectral analysis of the electroencephalogram (EEG) has been used to monitor depth of anesthesia. In the majority of publications this has been done using the so called Bispectral (BIS) Index. The exact relation of this index to bispectral quantities like the bispectrum and its normalized version the bicoherence has not yet been published. In case the EEG is a linear random process the bicoherence is trivial. It is a mere constant independent of the EEG frequency. If the signal is a linear Gaussian random process this constant is zero. In this case both the bispectrum and bicoherence are zero. The aim of this study was to determine the proportion of EEG epochs with non-trivial bicoherence during anesthesia with isoflurane/nitrous oxide.
We reanalyzed 26.4 hr of EEG signal recorded in 8 patients during anesthesia for general abdominal surgery which were stored in digitized form on CD-Rom. The test developed by Hinich for Gaussianity and linearity was applied to these data. The test was validated with various kinds of surrogate data; especially the phase randomized (pr) EEG, synthetic Gaussian random data and the z-component of the Lorenz attractor and its pr version.
The proportion of epochs for which a non-trivial bicoherence was detected by the test was as follows: Lorenz data 95%, pr Lorenz data 5%, synthetic Gaussian data 13.8%, pr EEG 5.4%, original EEG 6.2%.
As expected the test procedure correctly identified for the Lorenz data for 95% of all epochs a non-trivial bicoherence. For the original EEG data we could not find a significant greater percentage of epochs with non-trivial bicoherence than for the pr data and the synthetic Gaussian data. We conclude that the EEG during anesthesia with isoflurane/alfentanil appears to be largely a linear random process.
脑电图（EEG）的双谱分析已被用于监测麻醉深度。在大多数出版物中，这是通过所谓的双谱（BIS）指数来完成的。该指数与双谱量（如双谱及其归一化版本双相干）的确切关系尚未公布。如果脑电图是一个线性随机过程，双相干是平凡的。它仅仅是一个与脑电图频率无关的常数。如果信号是一个线性高斯随机过程，这个常数为零。在这种情况下，双谱和双相干都为零。本研究的目的是确定在异氟烷/氧化亚氮麻醉期间具有非平凡双相干的脑电图时段的比例。
我们重新分析了8例患者在全身腹部手术麻醉期间记录的26.4小时脑电图信号，这些信号以数字化形式存储在CD-ROM上。将Hinich开发的用于高斯性和线性的测试应用于这些数据。该测试用各种替代数据进行了验证；特别是相位随机化（pr）脑电图、合成高斯随机数据以及洛伦兹吸引子的z分量及其pr版本。
通过该测试检测到具有非平凡双相干的时段比例如下：洛伦兹数据95%，pr洛伦兹数据5%，合成高斯数据13.8%，pr脑电图5.4%，原始脑电图6.2%。
正如预期的那样，测试程序正确地识别出95%的洛伦兹数据时段具有非平凡双相干。对于原始脑电图数据，我们发现具有非平凡双相干的时段百分比并不比pr数据和合成高斯数据显著更高。我们得出结论，在异氟烷/阿芬太尼麻醉期间脑电图似乎在很大程度上是一个线性随机过程。
