[Bispectral analysis of EEG signal during focal cerebral ischemia].

Early noninvasive detection of cerebral ischemia is important for fighter pilots as well as in clinical diagnosis. In this paper, a model of focal cerebral ischemia was presented. Bispectrum of EEG signals recorded from ischemic region and normal region after 30 min ischemia was analyzed using the third-order recursion method, which possesses higher frequency resolving ability. It can resolve two closely spaced peaks in the bispectrum and detect the presence or absence of quadratic phase coupling at frequency pairs that are very close to each other. It was found that some characteristics of such bispectrum are very sensitive to focal cerebral ischemia. The maximum bispectrum magnitude of EEG and the weighted center of bispectrum (WCOB) changed sensitively to the different ischemic regions and ischemic stages. The ischemic and normal regions as well as the degree of ischemia can be clearly distinguished by analyzing their bispectrum of EEG. It demonstrates that this method can be used as a quantitative method for the detection of focal cerebral ischemia in the early phase.