Abstract
The human electroencephalogram (EEG) constitutes a nonstationary, nonlinear electrophysiological signal resulting from synchronous firing of neurons in thalamocortical structures of the brain. Due to the complexity of the brain's physiological structures and its rhythmic oscillations, analysis of EEG often utilises spectral analysis methods.Aim: to improve clinical monitoring of neurophysiological signals and to further explain basic principles of functional mechanisms in the brain during anaesthesia.Material and methods. In this paper we used Empirical Mode decomposition (EMD), a novel spectral analysis method especially suited for nonstationary and nonlinear signals. EMD and the related Hilbert-Huang Transform (HHT) decompose signal into constituent Intrinsic Mode Functions (IMFs). In this study we applied EMD to analyse burst-suppression (BS) in the human EEG during induction of general anaesthesia (GA) with propofol. BS is a state characterised by cyclic changes between significant depression of brain activity and hyper-active bursts with variable duration, amplitude, and waveform shape. BS arises after induction into deep general anaesthesia after an intravenous bolus of general anaesthetics. Here we studied the behaviour of BS using the burst-suppression ratio (BSR).Results. Comparing correlations between EEG and IMF BSRs, we determined BSR was driven mainly by alpha activity. BSRs for different spectral components (IMFs 1-4) showed differing rates of return to baseline after the end of BS in EEG, indicating BS might differentially impair neural generators of low-frequency EEG oscillations and thalamocortical functional connectivity.Conclusion. Studying BS using EMD represents a novel form of analysis with the potential to elucidate neurophysiological mechanisms of this state and its impact on post-operative patient prognosis.
Highlights
Несмотря на широкое повседневное использование общей анестезии (ОА) в практике, наше понимание нейрофизиологических особенностей ее механизмов все еще остается неполным [1]
This publication introduced the reader into the subject of Empirical Mode Decomposition (EMD) and its application to EEG analysis
In contrast with methods based on the Fourier transform, EMD does not assume the shape of its basis functions a priori, nor does it assume linearity or stationarity of the signal
Summary
Несмотря на широкое повседневное использование общей анестезии (ОА) в практике, наше понимание нейрофизиологических особенностей ее механизмов все еще остается неполным [1]. Общее поведение сигнала ЭЭГ во время ОА можно описать как замедление сигнала в сторону преобладания низкочастотных ( 4 Гц) колебаний с появлением глобальных медленных волн со всей поверхности головы [2,3,4]. Пропофол — наиболее часто используемый общий анестетик, применяемый для индукции ОА. Во время болюсной индукции ОА пропофолом клинически часто достигается транзиторное состояние очень глубокой анестезии, которое проявляется в виде быстрого замедления ритмов ЭЭГ с последующим относительно быстрым наступлением фармакологически индуцированного паттерна «вспышкаподавление» (ПВП), длящегося несколько. One of the promising sources of information about this state is the electroencephalogram (EEG) and its processed analysis. The generic behaviour of EEG signal during GA can be described as a slowing of the signal towards low-frequency ( 4Hz) oscillations with appearance of global slow waves across the scalp [2–4 ]
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