失神癫痫儿童不同导联脑电锁相平均波形的相位差

Phase differences in different electrodes phase-lock average waveforms of EEG in child with absence epilepsy

目的：研究失神癫痫儿童（CAE）不同导联脑电图锁相平均波形之间的相位关系。方法：记录15例CAE发作期和12例正常对照安静闭目脑电图，采样频率200Hz，采样时间20s。对脑电信号进行30个尺度的连续子波变换，用锁相条件采样和相位平均技术提取不同导联、不同尺度脑电信号多尺度锁相平均波形，用互相关函数计算不同导联不同尺度的EEG锁相平均波形的相位差，并与12例正常儿童脑电锁相平均波形进行比较，研究CAE不同导联不同尺度脑电锁相平均波形之间的相位关系。结果：正常儿童不同导联脑电信号存在相位差，额部导联的相位平均波形超前枕部的相位平均波形的相位大约为120°。CAE发作期脑电信号额部与枕部导联脑电锁相平均波形的相位差存在两种类型，一种是额部与枕部导联脑电同步相位平均波形的相位差消失，各导联相位平均波形趋于同步；另一种是额部与枕部导联脑电相位平均波形的相位差大约为180°，即相位相反。结论：本研究采用锁相条件采样和相位平均技术获得了不同导联之间的相位差，从新的角度研究了癫痫发作期脑电信号的相位关系。结果表明CAE发作期脑电信号不同导联之间的相位差与正常儿童存在差异，而且存在两种形式，其电生理机制还有待于进一步研究。

Objective：To investigate the EEG phase difference in different electrodes in child with absence epilepsy （CAE） and compare the patients with CAE with normal controls. Methods： Digital EEG signals of 15 patients with CAE and 12 normal children were recorded with sampling rate 200 Hz and sampling time 20s. Epileptic discharge signals during clinical and sub-clinical seizures were collected 10 and 20 times respectively. Continuous wavelet transforms were employed to unfold the digital EEG signals into components of 30 scales. The phase-lock average waveforms （PLAW） in different electrodes were obtained by phase-lock conditional sampling and phase-lock average techniques. The phase differences in electrodes were determined by correlation functions for PLAW. The phase difference in electrodes of PLAW in CAE were compared with that of the normal controls, Results： There existed phasedifference of PLAW in different electrodes for normal controls. The phase of forehead lead PLAW was ahead of occipital lead about 120° for normal controls. There were two types of phase-difference for CAE. One type showed that PLAW. synchronized for all electrodes while in another type the phase-difference between forehead lead and occipital lead was about 180°. Conclusion：Phase-lock conditional sampling and phase-lock average techniques can be employed to obtain the phase-difference of PLAW in different EEG electrodes. The study shows that the phase-difference in different EEG electrodes for CAE is different from that of normal controls and there are two types of phase-difference for CAE, and their mechanism remains to be further explored.