Institute of Electrical Engineering, Yanshan University, Qinhuangdao 066004, China.
Clin Neurophysiol. 2012 Apr;123(4):681-8. doi: 10.1016/j.clinph.2011.08.027. Epub 2011 Oct 10.
The Hurst exponent (HE) is a nonlinear method measuring the smoothness of a fractal time series. In this study we applied the HE index, extracted from electroencephalographic (EEG) recordings, as a measure of anesthetic drug effects on brain activity.
In 19 adult patients undergoing sevoflurane general anesthesia, we calculated the HE of the raw EEG; comparing the maximal overlap discrete wavelet transform (MODWT) with the traditional rescaled range (R/S) analysis techniques, and with a commercial index of depth of anesthesia - the response entropy (RE). We analyzed each wavelet-decomposed sub-band as well as the combined low frequency bands (HEOLFBs). The methods were compared in regard to pharmacokinetic/pharmacodynamic (PK/PD) modeling, and prediction probability.
All the low frequency band HE indices decreased when anesthesia deepened. However the HEOLFB was the best index because: it was less sensitive to artifacts, most closely tracked the exact point of loss of consciousness, showed a better prediction probability in separating the awake and unconscious states, and tracked sevoflurane concentration better - as estimated by the PK/PD models.
The HE is a useful measure for estimating the depth of anesthesia. It was noted that HEOLFB showed the best performance for tracking drug effect.
The HEOLFB could be used as an index for accurately estimating the effect of anesthesia on brain activity.
Hurst 指数（HE）是一种测量分形时间序列平滑度的非线性方法。本研究应用从脑电图（EEG）记录中提取的 HE 指数作为测量麻醉药物对大脑活动影响的指标。
在 19 名接受七氟醚全身麻醉的成年患者中，我们计算了原始 EEG 的 HE；比较了最大重叠离散小波变换（MODWT）与传统重标极差（R/S）分析技术，以及商业麻醉深度指数 - 反应熵（RE）。我们分析了每个小波分解的子带以及组合的低频带（HEOLFBs）。比较了这些方法在药代动力学/药效学（PK/PD）建模和预测概率方面的表现。
随着麻醉深度的加深，所有低频带的 HE 指数都降低了。然而，HEOLFB 是最好的指数，因为：它对伪影不敏感，最接近意识丧失的确切点，在区分清醒和无意识状态方面具有更好的预测概率，并且更好地跟踪七氟醚浓度 - 如 PK/PD 模型估计的那样。
HE 是估计麻醉深度的有用指标。研究发现，HEOLFB 在跟踪药物作用方面表现最佳。
HEOLFB 可作为准确估计麻醉对大脑活动影响的指标。
