Electrical and Computer Science Engineering, Monash University, Clayton, Vic, Australia.
Biomed Eng Online. 2010 Nov 20;9:76. doi: 10.1186/1475-925X-9-76.
Changes in nonlinear neuronal mechanisms of EEG generation in the course of general anaesthesia have been extensively investigated in research literature. A number of EEG signal properties capable of tracking these changes have been reported and employed in anaesthetic depth monitors. The degree of phase coupling between different spectral components is a marker of nonlinear EEG generators and is claimed to be an important aspect of BIS. While bicoherence is the most direct measure of phase coupling, according to published research it is not directly used in the calculation of BIS, and only limited studies of its association with anaesthetic depth and level of consciousness have been published. This paper investigates bicoherence parameters across equal band and unequal band bifrequency regions, during different states of anaesthetic depth relating to routine clinical anaesthesia, as determined by visual inspection of EEG.
41 subjects scheduled for day surgery under general anaesthesia were recruited into this study. EEG bicoherence was analysed using average and smoothed-peak estimates calculated over different regions on the bifrequency plane. Statistical analysis of associations between anaesthetic depth/state of consciousness and bicoherence estimates included linear regression using generalised linear mixed effects models (GLMs), ROC curves and prediction probability (Pk).
Bicoherence estimates for the δ_θ region on the bifrequency plane were more sensitive to anaesthetic depth changes compared to other bifrequency regions. Smoothed-peak bicoherence displayed stronger associations than average bicoherence. Excluding burst suppression and large transients, the δ_θ peak bicoherence was significantly associated with level of anaesthetic depth (z = 25.74, p < 0.001 and R2 = 0.191). Estimates of Pk for this parameter were 0.889(0.867-0.911) and 0.709(0.689-0.729) respectively for conscious states and anaesthetic depth levels (comparable BIS estimates were 0.928(0.905-0.950) and 0.801(0.786-0.816)). Estimates of linear regression and areas under ROC curves supported Pk findings. Bicoherence for eye movement artifacts were the most distinctive with respect to other EEG patterns (average |z| value 13.233).
This study quantified associations between deepening anaesthesia and increase in bicoherence for different frequency components and bicoherence estimates. Increase in bicoherence was also established for eye movement artifacts. While identified associations extend earlier findings of bicoherence changes with increases in anaesthetic drug concentration, results indicate that the unequal band bifrequency region, δ_θ, provides better predictive capabilities than equal band bifrequency regions.
在全身麻醉过程中，脑电图生成的非线性神经元机制的变化已在研究文献中得到广泛研究。已经报道了许多能够跟踪这些变化的 EEG 信号特性，并将其用于麻醉深度监测器。不同频谱分量之间的相位耦合程度是 EEG 发生器非线性的标志，据称是 BIS 的一个重要方面。虽然双相干是相位耦合的最直接度量，但根据已发表的研究，它并未直接用于 BIS 的计算，并且仅发表了有限的关于其与麻醉深度和意识水平关系的研究。本文研究了与常规临床麻醉相关的不同麻醉深度状态下，双频区域等频带和非等频带双频区域的双相干参数，这些状态是通过 EEG 的视觉检查确定的。
这项研究招募了 41 名计划在全身麻醉下进行日间手术的患者。使用在双频平面上不同区域计算的平均和平滑峰值估计值分析 EEG 双相干。使用广义线性混合效应模型（GLM）、ROC 曲线和预测概率（Pk）对麻醉深度/意识状态与双相干估计值之间的关联进行线性回归的统计分析。
与其他双频区域相比，双频平面上 δ_θ 区域的双相干估计值对麻醉深度变化更敏感。平滑峰值双相干比平均双相干具有更强的相关性。排除爆发抑制和大瞬变后，δ_θ 峰双相干与麻醉深度水平显著相关（z = 25.74，p < 0.001，R2 = 0.191）。对于该参数的 Pk 估计值分别为 0.889（0.867-0.911）和 0.709（0.689-0.729），用于意识状态和麻醉深度水平（可比的 BIS 估计值分别为 0.928（0.905-0.950）和 0.801（0.786-0.816））。线性回归估计和 ROC 曲线下面积支持 Pk 结果。眼动伪影的双相干与其他 EEG 模式相比最具特色（平均 |z| 值为 13.233）。
本研究量化了不同频率成分和双相干估计值与麻醉深度加深之间的关联。也确定了眼动伪影的双相干增加。虽然已经确定的关联扩展了先前关于麻醉药物浓度增加时双相干变化的发现，但结果表明，非等频带双频区域 δ_θ 比等频带双频区域提供了更好的预测能力。
