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Biomedical subjects

I Gath

Publications and source records attributed to I Gath.

At least 37 records · Page 2Linked to original sources
PubMed1993

Effects of sodium butyrate on DNA content, glutathione S-transferase activities, cell morphology and growth characteristics of rat liver nonparenchymal epithelial cells in vitro.

The effects of sodium butyrate, which has been shown to act as a differentiation promoting agent in several different tumor cell lines, were studied in a rat liver nonparenchymal epithelial cell line. Exposure of these cells to 3.75 mM butyrate resulted in an inhibition of cell proliferation and, at the same time, an increase in cell diameter (2- to 6-fold) and size of the nuclei (approximately 2-fold) after 3 days in culture. Binucleated cells arose, comprising approximately 12% of the cells investigated, and the number of cells with an abnormal set of chromosomes was increased. Intercellular communication, measured by dye transfer of Lucifer Yellow, was unchanged. From the various xenobiotic metabolizing enzyme activities measured, only those of glutathione S-transferases were significantly altered (increases of 4- to 9-fold) by butyrate treatment. These increases were mainly due to the predominant rise in the pi class isoenzyme which is a well-known tumour marker in rat hepatocarcinogenesis. Thus, our results cannot be interpreted as being either due to promotion of differentiation or due to transformation. The state and type of cell under study has to be considered and investigations of further differentiation parameters are needed to obtain a deeper insight into the biological activity and the underlying mechanisms of cell state modifying agents like butyrate.

Animals↗
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↗
PubMed1991

High resolution pole-zero analysis of parkinsonian speech.

High resolution analysis of voiced speech signals in Parkinsonian patients using a pitch synchronous pole-zero model is introduced. A modified estimation error is defined leading to an accurate and consistent determination of the excitation instants of the model. An infinite resolution in determining these instants, despite the finite sampling interval, is achieved by mapping the discrete (digitized) problem into a continuous one. The proposed analysis was found to be useful in analyzing Parkinsonian speech where the goal was to detect and quantify the Parkinsonian tremor and rigidity from sustained voiced sounds.

Electromyography↗
PubMed1989

Segmentation of EEG during sleep using time-varying autoregressive modeling.

Time-varying AR modeling is applied to sleep EEG signal, in order to perform parameter estimation and detect changes in the signal characteristics (segmentation). Several types of basis functions have been analyzed to determine how closely they can approximate parameter changes characteristic of the EEG signal. The TV-AR model was applied to a large number of simulated signal segments, in order to examine the behaviour of the estimation under various conditions such as variations in the EEG parameters and in the location of segment boundaries, and different orders of the basis functions. The set of functions that is the basis for the Discrete Cosine Transform (DCT), and the Walsh functions were found to be the most efficient in the estimation of the model parameters. A segmentation algorithm based on an "Identification function" calculated from the estimated model parameters is suggested.

Algorithms↗
PubMed1988

Analysis of vocal tract parameters in parkinsonian speech.

A method for the analysis of vocal tract parameters is developed, aimed to perform quantitative analysis of rigidity from speech signals of Parkinsonian patients. The cross-sectional area function of the vocal tract is calculated using pitch synchronous autoregressive moving average (ARMA) analysis. The changes in Parkinsonian subjects of the cross-sectional area during the utterance of sustained sounds are attributed to both Parkinsonian tremor and rigidity. In order to isolate the effects of the rigidity on the vocal tract from those of the tremor, an adaptive tremor cancellation (ATC) algorithm is developed, based on the correlation of tremor signals extracted from different locations of the speech production system.

Algorithms↗
PubMed1986

Simulation of the spatial distribution of muscle fibres in human muscles.

A composite muscle cross section model was simulated on a VAX 780 computer. The various motor unit territories in the cross section area were circular, partially overlapping each other. The radii of the territories of the motor units, their centres, and the number of muscle fibres in each motor unit were treated as random variables. Two different models were generated, one with a uniform distribution of the fibres in the motor unit territories, and the other with a normal distribution of the fibres. An algorithm for simulation of fibre density measurements was written, and the effects of varying the parameters of the model on fibre density measurements were investigated. The results of the computer simulation were in agreement with analytical and laboratory findings.

Computers↗
PubMed1985

Automatic classification of visual evoked responses.

An automatic method performing selective averaging of visual evoked potentials depending on the state of the EEG background activity is described. The method is based on adaptive segmentation of the EEG signal and on fuzzy clustering. A simulation example, extracting two different square pulses from the background activity, is given, as well as an example averaging two types of visual evoked potentials from the background EEG signal.

Adult↗
PubMed1984

Electrophysiological aspects of benzodiazepine antagonists, Ro 15-1788 and Ro 15-3505.

The comparative action of two specific benzodiazepine antagonists, Ro 15-1788 and Ro 15-3505 was examined in six healthy volunteers. Medication was given i.v. in a double-blind cross over pattern, and EEG was recorded throughout each experimental session. Ten minutes after the injection of one of the antagonists or placebo, midazolam was injected in incremental doses until first signs of drowsiness appeared in the EEG. The EEG was computer analyzed, using adaptive segmentation and time-dependent clustering. Continuous power profiles for various frequency bands, as well as power ratios for the physiological frequency bands (e.g. sigma/alpha power ratio) were generated. It has been found that sigma/alpha power ratio was the most sensitive parameter detecting early effects of midazolam on the EEG signal, thus enabling a semi-quantitative titration of the antagonists by midazolam. Ro 15-1788 in doses of 5 mg i.v. was counteracted on average by 7.3 mg midazolam. From the EEG analysis it has been found that Ro 15-3505 was at least 4-5 times more potent than Ro 15-1788.

Adult↗
PubMed1983

Automatic scoring of polygraphic sleep recordings: midazolam in insomniacs.

Midazolam in doses of 0.21-0.46 mg/kg was given to four insomniacs for 27 days, and to a fifth insomniac for an additional 124 days, to assess its short, intermediate, long-term and long-standing efficacy. Automatic analysis of the polygraphic sleep recordings was carried out employing real-time signal processing (based on linear prediction), and an off-line sequential fuzzy clustering. Total sleep length did not vary significantly during medication, whereas other efficacy parameters such as sleep onset latency, wake time after sleep onset and number of nightly awakenings decreased significantly throughout the period of active medication. In one patient, midazolam was still effective after 151 days of administration. The ultrashort action (probably 3-4 h) of midazolam could be demonstrated by the distribution of the efficacy parameters, dividing the night into 2-h periods, by the unchanged total sleep length during medication compared with baseline and by the lack of any subjective clinical symptoms of hangover. The quantitative analysis of the signals showed that, although a decrease in the total amount of slow-wave sleep during long-term medication and withdrawal was detected, the total relative power in the delta band increased during drug administration. This was interpreted as redistribution of the delta activity during active medication. A lengthening of REM sleep was found during active medication probably attributable to intranight rebound. This was not followed by any clinical symptom of clinical REM rebound.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Fuzzy clustering of EEG signal and vigilance performance.

An automatic method for classification of EEG data, based upon segmentation of the signal using the autoregressive model and decision making in fuzzy environment, is described. The classification is applied to explore the relations between EEG states during waking, and vigilance performance studied through auditory choice reaction time. The average auditory choice reaction time measured during occurrences of "alpha" segments was significantly shorter than that measured during occurrences of "nonalpha" signal segments. A significant negative correlation was also found between the segments auditory choice reaction time and the segments spectral power in the alpha or beta frequency band.

Adult↗
PubMed1983

Classical sleep stages and the spectral content of the EEG signal.

Polygraphic sleep recordings during 12 nights in 5 healthy volunteers were classified manually into waking and the various sleep stages. The smoothed power spectra of EEG signal segments defined as waking or one of the sleep stages were calculated via segmentation of the EEG signal, using the autoregressive model, and time-dependent fuzzy clustering. The spectra were derived from the prediction coefficients of the segments. The relative power in the delta frequency band was found to increase monotonically with increasing depth of sleep, together with a parallel decrease in the alpha relative power. In most cases alpha relative power had a small peak during REM sleep, and on average the relative power in the sigma frequency band during REM sleep was smaller than the beta relative power. The power spectra from subjects with no waking alpha differed from those of subjects with abundant waking alpha mostly in the relative spectral content of stages 1 and REM. The significance of these findings is discussed in relation to future standardisation of automatic analysis of sleep recordings.

Adult↗
PubMed1982

On the measurement of fibre density in human muscles.

A computer simulation model and an analytical model simulating the measurement of fibre density during single fibre electromyography is described. The relation between the measured fibre density (including the triggering fibre) and the true theoretical fibre density (including in the measurement also positions with zero fibre counts) is derived. A good agreement was found between the two models, and between laboratory values for fibre density measurements and count histograms. The assumption of a uniform distribution of the fibres in the motor unit territory vs. a Gaussian distribution of the fibres is discussed.

Electromyography↗
PubMed1981

In situ measurement of the innervation ratio of motor units in human muscles.

Volume conduction measurements were carried out the brachial biceps, tibialis anterior and deltoid, in normal human subjects. Attenuation constant K and time constant tau of the muscle tissue transfer function were measured, and the average electrode uptake area calculated for the three muscles. The average number of muscle fibres in the motor unit, i.e., the innervation ratio, was calculated from the electrode uptake area, data on the motor unit territory, and measurements of fibre density. The innervation ratios for the brachial biceps, tibialis anterior and deltoid were 209, 329, and 239 fibres, respectively. It was found that the anatomical scatter of fibers belonging to the same motor unit was smaller in brachial biceps than in tibialis anterior, whereas the electrophysiological "fibre density" was higher in tibialis anterior. The implications of these findings for the interpretation of normal and abnormal electromyographic findings are discussed.

Evoked Potentials↗