TY - JOUR AU - Broek, P.L.C. van den AU - Rijn, C.M. van AU - Egmond, J. van AU - Coenen, A.M.L. AU - Booij, L.H.D.J. PY - 2006 UR - https://hdl.handle.net/2066/50614 AB - BACKGROUND AND OBJECTIVE: Anaesthesiologists need parameters that measure the depth of anaesthesia. In the context of this need, the present study investigated in rats how two variables from the electroencephalogram, the burst suppression ratio and effective correlation dimension correlated with a measure of anaesthetic depth as measured in the strength of a noxious withdrawal reflex. METHODS: Eight rats were exposed to different inspiratory concentrations of sevoflurane, each rat in two separate experiments. In the first experiment, spontaneously breathing animals could move freely and no painful stimuli were applied. In the second experiment, in mechanically ventilated restrained anaesthetized rats, the withdrawal reflex was measured every 80 s. In both experiments the electroencephalogram was continuously recorded. The concentration in the effector compartment was estimated using a first order two compartment model. Correlation dimension was computed following the Grassberger/Procaccia/Takens approach with optimized parameter settings to achieve maximum sensitivity to anaesthetic drug effects and enable real-time computation. The Hill, equation was fitted to the data, describing the effect as a function of sevoflurane concentration. RESULTS: Good correlations of Depth of Anaesthesia with correlation dimension as well as burst suppression ratio were established in both types of experiments. Arousal by noxious stimuli decreased burst suppression ratio and increased correlation dimension. The effective sevoflurane concentration associated with 50% of the maximum effect (C50) was higher in experiment II (stimulation) than in experiment I (no stimulation): i.e. for correlation dimension 2.18% vs. 0.60% and for burst suppression ratio 3.07% vs. 1.73%. The slope factors were: gammaCD = 4.15 vs. gammaCD = 1.73 and gammaBSR = 5.2 vs. gammaBSR = 5.4. Correlation dimension and burst suppression ratio both correlated with the strength of the withdrawal reflex with correlation coefficients of 0.46 and 0.66 respectively (P < 0.001). CONCLUSIONS: Both correlation dimension and burst suppression ratio are related to anaesthetic depth and are affected by noxious stimuli. The relationship between anaesthetic depth and burst suppression ratio is confirmed and the potential of correlation dimension is demonstrated. TI - An effective correlation dimension and burst suppression ratio of the EEG in rat. Correlation with sevoflurane induced anaesthetic depth. EP - 402 SN - 0265-0215 IS - iss. 5 SP - 391 JF - European Journal of Anaesthesiology VL - vol. 23 DO - http://dx.doi.org/10.1017/S0265021505001857 ER - TY - JOUR AU - Broek, P.L.C. van den AU - Rijn, C.M. van AU - Egmond, J. van AU - Coenen, A.M.L. AU - Booij, L.H.D.J. PY - 2006 UR - https://hdl.handle.net/2066/56943 AB - Although brain signals measured under the skull (electrocorticogram, ECoG) and signals measured on top of the scalp (electroencephalogram, EEG) stem from the same brain activity, they are different. We investigated how we can produce EEG when we know ECoG ("forward problem") and how we can produce ECoG when we know EEG ("inverse problem"). We modeled the head as three concentric spheres, representing the brain, skull and scalp. Brain activity is simulated by a dipole. The forward method links the ECoG potentials on the inner sphere to the EEG potentials on the outer sphere via a transfer matrix, based on the geometries and the conductivities of tissues involved. Results showed that the error between analytically computed EEG and EEG produced from analytically produced ECoG with the forward method, is smaller at electrodes close to the source, compared to electrodes far away from the source. The higher the resolution of an ECoG electrode grid, the better the forward model works. Another finding was that the forward model is more accurate or surface sources, compared to deep sources. This result is of practical importance, since most cognitive interesting sources stem from the cortex (the outermost layer of the brain). In the inverse model, the transfer matrix is inverted and additional regularization constraints are applied to compute ECoG from simulated EEG. We showed that the inverse model gives good results. The forward method is tested with data measured from an epileptic patient at the University of Freiburg. Results show that the forward model gives better results at the EEG electrode overlying the ECoG grid compared to the electrode posterior to the grid. Further research is needed to make errors smaller. TI - An effective correlation dimension and burst suppression ratio of the EEG in rat. Correlation with sevoflurane induced anaesthetic depth EP - 402 SN - 0265-0215 IS - iss. 5 SP - 391 JF - European Journal of Anaesthesiology VL - vol. 23 PS - 12 p. DO - http://dx.doi.org/10.1017/S0265021505001857 ER - TY - JOUR AU - Broek, P.L.C. van den AU - Egmond, J. van AU - Rijn, C.M. van AU - Takens, F. AU - Coenen, A.M.L. AU - Booij, L.H.D.J. PY - 2005 UR - https://hdl.handle.net/2066/47849 TI - Feasibility of real-time calculation of correlation integral derived statistics applied to EGG time series EP - 208 SN - 0167-2789 IS - iss. 3-4 SP - 198 JF - Physica D-Nonlinear Phenomena VL - vol. 203 DO - https://doi.org/10.1016/j.physd.2005.03.012 ER - TY - JOUR AU - Broek, P.L.C. van den AU - Egmond, J. van AU - Rijn, C.M. van AU - Takens, F. AU - Coenen, A.M.L. AU - Booij, L.H.D.J. PY - 2005 UR - https://hdl.handle.net/2066/56948 AB - This study assessed the feasibility of online calculation of the correlation integral (C(r)) aiming to apply C(r)-derived statistics. For real-time application it is important to reduce calculation time. It is shown how our method works for EEG time series. Methods: To achieve online calculation of C(r) a non-randomly subset of inter vector distances was chosen and computer code was optimized. The effect of distance exclusion was investigated for both non-randomly and randomly chosen subsets. A C(r)-derived statistic was computed: an effective correlation dimension (CD) following the Grassberger-Procaccia-Takens approach. Results: By taking a subset of the maximum possible number of distances, C(r)-computation time could be easily 100 times reduced with marginal changes and minor variability in the C(r)-derived statistic CD. Applied to the EEG CD gives a good indication of the depth of anesthesia. Conclusions: If applied to the EEG, apparently a large number of distances can be omitted in the calculation of C(r) with minimal consequences. This outcome confirms Hoeffding's theory of U-statistics and hence it is expected to occur generally, also for non-EEG time series. TI - Feasibility of real-time calculation of correlation integral derived statistics applied to EEG time series EP - 208 SN - 0167-2789 IS - iss. 3 SP - 198 JF - Physica D-Nonlinear Phenomena VL - vol. 203 DO - https://doi.org/10.1016/j.physd.2005.03.012 ER - TY - CONF AU - Broek, P.L.C. van den AU - Egmond, J. van AU - Rijn, C.M. van AU - Dirksen, R. AU - Coenen, A.M.L. AU - Booij, L.H.D.J. PY - 2000 UR - http://repository.ubn.ru.nl/handle/2066/126744 AB - To find a new measure from the EEG that quantifies the effects of anesthetics during surgery, the correlation dimension (CD) of the EEG of eight rats was estimated. To get informed about the anesthetic state, the noxious induced withdrawal reflex (NIWR) was measured, i.e. the force elicited by transcutaneous electrical stimulation of the hind paw. The algorithm of Grassberger and Procaccia (1983) to compute the CD was slightly modified and labeled as "dimensional complexity" (DC). The DC was estimated by applying a fit procedure to find the scaling region in the correlation integral. Experiments were performed under propofol infusion (30 à 40 mg.kg-1.h-1), with repeated bolus injections (3 mg) to induce periods of more profound anesthesia. The DC was compared to the Spectral Edge Frequency (SEF), a linear measure extracted from the power spectrum. The DC and SEF were correlated with the NIWR responses. The DC showed higher and more consistent correlations with the NIWR than the SEF. Correlation coefficients of NIWR and DC mainly varied between 0.6 and 0.8. Conclusion: New parameters from the field of non-linear dynamics can be an aiding tool in detecting effectual changes induced by anesthetics. PB - Singapore : World Scientific TI - The application of a non-linear analysis technique to the monitoring of anesthetic effects in the rat EP - 262 SP - 259 CT - Lehnertz, K.; Elger, C.E.; Arnhold, J. (ed.), Chaos in the brain. Proceedings of the 1999 Workshop ER -