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Two new surrogate methods, the Small Shuffle Surrogate (SSS) and the Truncated Fourier Transform Surrogate (TFTS), have been proposed to study whether there are some kind of dynamics in irregular fluctuations and if so whether these dynamics are linear or not, even if this fluctuations are modulated by long term trends. This situation is theoretically incompatible with the assumption underlying previously...
During epilepsy seizure Electrocorticogram (ECoG) may change dramatically from a nearly chaotic signal (basal state) into a highly synchronized signal during a seizure, characterized by high amplitude and low frequency, and suddenly go back to the basal sate, making hard to identify them from time series. The epileptic seizure shows some stages as it is evolving, the here studied are: basal, preictal,...
A methodology for identifying brain areas from the brain MER signals (microelectrode recordings) is presented, which is based on a nonlinear feature set. We propose nonlinear dynamics measures such as correlation dimension, Hurst exponent and the largest Lyapunov exponent to characterize the dynamic structure. The MER records belong to the Polytechnical University of Valencia, 24 records for each...
Heat-stressed poultry can suffer high mortality rates when air velocity in the microenvironment around the chickens falls below a minimum threshold level. The current designs of ventilation systems and buildings are able to create suitable air velocities in the zone occupied by animals and can be evaluated by computational fluid dynamics (CFD) techniques. However, it is still important to experimentally...
An Electrocorticogram (ECoG), during an epilepsy episode can change dramatically from the normal state into a high amplitude low frequency signal and suddenly return to the normal sate. It is possible to identify some stages in the epilepsy seizure, the most representative of them: basal, preictal, ictal and posictal. ECoG are highly non periodical signals, so they are analyze with T-F algorithms,...
Rheoencephalography (REG) is impedance plethysmography applied to the head, and provides an indirect measurement of the pulsatility of the cerebral blood volume. To extend REG as a clinical and research tool, it is necessary to evaluate the sensitivity of REG measurement to local brain conductivity changes. By means of the analytical solution of a four-sphere geometrical model of the head, maps of...
The well-known inherent artifact on the rheoencephalogram (REG) caused by the pulsatility of the scalp blood flow left the REG out of the clinical practice. In fact, depending on the selected electrode arrangement, the measurement of the brain impedance changes time-locked with the heartbeat can be completely buried on that of the scalp. In this work, a novel mathematical method based on the physiological...
Hidden Markov Models have shown promising results for identification of spike sources in Parkinson's disease treatment, e.g., for deep brain stimulation. Usual classification criteria consist in maximum likelihood rule for the recognition of the correct class. In this paper, we present a different classification scheme based in proximity analysis. For this approach matrices of Markov process are transformed...
Objectives: Partial contributions of intracranial and extracranial circulation to rheoencephalography (REG) remain uncertain. The main goal of this work is to determine theoretically the capability of REG techniques to reflect intracranial blood flow.Methods: Head and current injection electrodes were computationally modeled to assess REG sensitivity to brain and scalp conductivity changes. Data obtained...
A method for cardiac cycle related signals standardization is presented. It provides better reproductibility of original signals than the linear interpolation method, maintaining the original waveshape on selected areas. This new method could be useful in the processing of cardiac related signals and in ECG data reduction techniques.
Different parameters are suggested to evaluate the compression techniques for ECG signals. These criteria are applicated to compare the Fourier Series Development (FSD), Discrete Cosine Transform (DCT) and Minimal Square (MS). New criteria based on the Correlation Factor (CF) between the last parameters stored and the parameters of the new cycle are also presented.
The action potential event is explained, making use of a membrane model that includes an electromechanical action, such as electrostatic compression. The model shows the permeability modulation induced by potential changes and explains the ionic transfer phenomena (sodium input in the rising phase and the delayed output of potassium in the decaying phase). Other associated phenomena, such as accommodation,...
Preliminary results relating to heart-synchronized evoked potentials (HSEP) are presented. In contrast with conventional methods, the authors have used an integral stimulus source, the heart, for triggering the EEG data acquisition process. The HSEPs are obtained by averaging a number of such heart synchronized data. HSEPs are easily recorded after a few tenths of EEG cycles, preliminary experiments...
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