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Biomedical subjects

I Gath

Publications and source records attributed to I Gath.

13 recordsLinked to original sources
PubMed1992

On the tracking of rapid dynamic changes in seizure EEG.

Estimation of autospectra and coherence and phase spectra of seizure EEG, using the FFT technique, will cause "smearing" of the rapid dynamic changes which occur during the seizure. This is inherent to FFT spectral estimation, due to the averaging process which is necessary in order to get consistent spectral estimates. A different approach suggested in the present study is to carry out multivariate autoregressive modeling of the multichannel seizure EEG, combined with adaptive segmentation. In order to obtain good estimates in cases of short record length, the vectorial AR modeling was based on residual energy ratios. The method has been tested on multichannel seizure EEG recordings from rats with focal epilepsy, caused by intracerebral administration of Kainic acid, and in depth EEG recordings in patients with temporal lobe epilepsy.

Animals↗
PubMed1991

A model for dual channel segmentation of the EEG signal.

Dual channel segmentation of the EEG signal has been developed. The purpose was to divide the signals into segments, according to information common for the two channels. The criterion for segmentation was based on the changes in the cross-spectrum of the two signals. It has been shown theoretically, as well as by simulation studies and by analysis of real EEG data that this method is sensitive to changes common for both channels, whereas segmentation does not occur as a result of changes in each channel separately.

Algorithms↗
PubMed1979

An iterative algorithm for the separation of action potential sequences.

Various iterative algorithms for separation of superimposed event sequences were designed, and their efficiency examined through simulation studies. It has been found that a double parallel-serial algorithm improved markedly the efficiency of the filtration process. For the same probability of detection of the event series to be extracted, the probability of 'impurity' events dropped by roughly 0.10, as compared to the non-iterative fixed window width algorithm. Conclusions are drawn regarding separation of motor unit action potential sequences from the total electromyogram.

Action Potentials↗
PubMed1979

Time and frequency analysis of simultaneously recorded corneal and non-corneal electroretinogram.

Electroretinograms (ERGs) were simultaneously recorded with corneal and non-corneal (lower or upper eye lid) electrodes in four healthy subjects. 64 traces of the non-corneal ERG were averaged. The two signals were compared in both time and frequency domains. The power spectrum of both signals was computed by the fast Fourier (FFT) and linear prediction (LP) algorithms. Except for amplitude differences, the two signals had almost identical time domain (a- and b-wave latencies) and frequency domain (dominant power spectrum peaks) parameters. It is concluded that non-corneal ERG does not differ significantly from corneal ERG, and that its clinical interpretation can be based on existing corneal ERG data.

Adult↗
PubMed1978

Screening of patients with Huntington's chorea by pneumoencephalography: criteria for decision and probability of error.

The problem of making a decision in case of two clinical hypotheses is treated by the application of the Neyman-Pearson criterion. As an example, a pneumoencephalographic index (frontal horn width divided by septum-caudate distance) of two different diseases, Huntington's chorea and Parkinsonism, is analyzed. As the aim of the investigator is to detect the maximum number of cases of Huntington's chorea, an appropriately high alpha, (the probability of "false alarm") should be chosen, and maximization of 1-beta (the probability of detection of Huntington's chorea) carried out.

Humans↗
PubMed1978

The calculated radial decline of the extracellular action potential compared with in situ measurements in the human brachial biceps.

Action potentials from 16 single muscle fibres were recorded with a multi-electrode from the human brachial biceps. Propagation velocity was calculated for 10 of the fibres, and the volume conduction at distances of 79, 152 and 251 micrometer, was measured for 6 of these fibres. The radial decline of the action potentials was calculated from the Fourier transform of the action potential at the origin, simulating the low-pass filter characteristics of the muscle tissue by sections of RC elements. A good agreement was found between the calculated data and the experimental data on the radial decline of the action potentials. The 90% attenuation radius of the action potential recorded with a 25 micrometer electrode, calculated for 16 action potentials, was derived from the volume conduction calculations. The average value found was 191 +/- 20 micrometer. A linear correlation was found between this radius and the peak spectral amplitude of the action potentials. Likewise, a linear correlation between the 90% attenuation radius and the propagation velocity of the fibres was confirmed.

Action Potentials↗
PubMed1977

On the volume conduction in human skeletal muscle: in situ measurements.

Volume conduction was studied in situ in human skeletal muscle, using a "single fibre multielectrode". The multielectrode was inserted perpendicular to the fibre axis, and the same single fibre action potential was recorded consecutively from 4 neighbouring leading-off surfaces. The transfer functions of 10 sections of muscle tissue lying between pairs of neighbouring electrodes were calculated from the Fourier transform of the input and output, i.e. the action potential recorded by the two neighbouring leading-off surfaces. The transfer function had one dominant pole, and was therefore modelled by a section of lumped RC elements The average gain factor and average time constant calculated from the transfer function for a muscle tissue section of 76 mu length were 0.55 and 69 musec, respectively. The radial attenuation of the different sinusoidal components of the extracellular action potential was calculated, and was found to be greater than previously reported in the literature, particularly for the slow frequency components. As an explanation of these findings, the possibility of a greater anisotropy of the muscle tissue than previously reported is discussed.

Action Potentials↗
PubMed1975

Penumoencephalographic findings in parkinsonism.

Pneumoencephalograms of 19 patients with unilateral parkinsonism, and of 26 patients with symptoms of generalized parkinsonism were studied. Cortical atrophy was found in 46.7% (21), while central (ventricular) atrophy occurred in 77.8% (35) of the patients. The percentage of patients with cortical atrophy, or with enlargement of ventricular body span (VBS) and septum-caudate distance (S-C), was smaller in the hemiparkinsonism group. No substantial correlation was found between enlargement of frontal horn width (FH), S-C and third ventricle width (3V), and the duration of illness. Likewise, no noteworthy correlation could be seen between the degree of central atrophy and the severity of the clinical symptoms. The FH/S-C ratio of the group of unilateral parkinsonism patients was higher than in the generalized parkinsonism group. The FH/S-C ratios in parkinsonism and in Huntington chorea patients varied. A ratio of greater than 1.40 was found in 73.3% of the patients with parkinsonism, and in an earlier study, it was found that 96.4% of the patients with Huntington chorea had a ratio less than 1.40. It is suggested that a FH/S-C ratio less than or equal to 1.40 is compatible with the diagnosis of Huntington chorea, although 26.7% (12) patients with parkinsonism have a ratio less than or equal to 1.40.

Adult↗
PubMed1975

On the separation of semiperiodic superimposed point processes: application to electromyographic signals.

A method for the separation of semiperiodic (Gaussian probability distribution of intervals with moderate coefficient of variation) superimposed point processes, to be implemented on a digital computer is described. The efficiency of the filter used for the extraction of the underlying event sequences from the pooled array has been investigated by simulation. Approximately 80 percent of the events belonging to the underlying sequence to be extracted were recovered (with the addition of "impurity events"), still preserving the mean rate and coefficient of variation of the original indicidual sequence concerned. The program was used on an example of an actual electromyographic recording (comprised of a number of motor units discharging simultaneously), resolving the number of motor units involved, their mean rates, and the coefficient of variation of the individual action potential sequences.

Action Potentials↗
PubMed1975

Frequency and time domain characteristics of single muscle fibre action potentials.

Action potentials of single muscle fibers (brachial biceps) were recorded with a multi-electrode, ensuring a minimum fibre-electrode recording distance. Propagation velocity was measured in 15 fibres and the power spectral density of the action potentials was computed through a FFT algorithm. Linear correlation was found between action potential amplitude (peak to peak) and propagation velocity, as well as between maximum-minimum amplitude time (defined as the time interval between the positive and negative peaks) and propagation velocity. Assuming al linear dependence between propagation velocity and muscle fibre diameter, a linear relation between the fibre thickness and the extra-cellular action potential was derived from the action potential amplitude/propagation velocity curve. The action potential power spectrum had a band pass form, with peak magnitude of 1.61+/-0.03 kc/sec, and -3 dB points at 0.98+/-0.19 kc/sec and at 2.41+/-0.53 kc/sec. A linear relation was found between the spectral peak magnitude and propagation velocity, and between the ban width and the propagation velocity, as predicted by a mathematical model describing the power spectrum of single fibre action potentials.

Action Potentials↗