SEARCH · PubMed Health

Results for “spectral analysis”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources

PubMed1976

A study of anaesthesia depth by power spectral analysis of the electroencephalogram (EEG).

The feasibility of using computer-based EEG spectral analysis to monitor the level of anaesthesia during nitrous oxide-alphaprodine anaesthesia has been established by this study. At present, this system is capable of estimating the level of anaesthesia correctly from 55 per cent to 80 per cent of the time. There are several possible clinical applications of such a monitoring system during anaesthesia. It provides a continuous estimation of the depth of anaesthesia, without requiring any special EEG training on the part of the anaesthetist. This system can also be of particular benefit during anaesthesia for critically ill patients, or in specific cases, as in neurosurgery and caesarian section when there may be periods of time when the gross clinical evaluation of depth of anaesthesia may not be precise or reliable and yet it is imperative not to deepen the anaesthesia unnecessarily. In such instances it appears that a monitoring system such as we have developed could provide valuable indication of the depth of anaesthesia. Other potential applications might be in the training of students in the clinical assessment of patients during anaesthesia and in the study of new anaesthetic agents.

Adult↗

PubMedDate not supplied

Power spectral analysis of auditory evoked response.

Five normal hearing adults were examined for power spectral analysis of AER to 1000-Hz pure tone. Major frequency components of responses to stimuli at 50 dB hearing level exist at 1 to 14 c/s. The power spectra of responses to stimuli at 10 dB hearing level are greater than those of the SBA in the frequency components between 3 and 9 c/s; furthermore, the total power of 3 to 9 c/s indicates a clear difference between the 2. Incidentally, at 512-msec analysis time, the total power of 3 to 9 c/s of the AER are significantly greater than that at 1024-msec analysis time, whereas those of the SBA show little discrepancy at the 2; thus at 512-msec analysis time, the total power of 4 to 9 c/s yields a clear difference between the AER and the SBA responses averaged over 50 stimuli even at 10 dB hearing level.

Adult↗

PubMed1979

Spectral analysis of EEG during mental activity (author's transl).

With the use of power spectral analysis, the occipital and frontal EEGs in normal young subjects were examined during mental activity under closed-eye and open-eye conditions. Under the closed-eye condition, the peak of power spectral density in the alpha band was suppressed during mental activity, as compared with the finding obtained without mental loading. Moreover, the peak frequency of the alpha band shifted to higher frequencies under the mental loading condition in all of the subjects. Under the open-eye condition, alpha waves were prominently suppressed and no peak of power spectral density in the alpha band could be detected. However, during mental activity the peak of power spectral density could be detected in the delta wave band of both occipital and frontal EEGs.

Adolescent↗

PubMed1979

Spectral analysis of urinary reactions: a preliminary study based on a novel concept.

The concept of spectral analysis of urinary reactions (a range of simple chemical tests combined with pattern analysis) is described. A preliminary study in which we used 10 nonspecific tested on untimed urine specimens from 20 controls and 20 diabetics, matched for age and sex, suggested that a combination of these tests could be used to separate diabetics from healthy subjects. This combination, however, did not prove satisfactory for a further group of 13 diabetics. Closer examination revealed that factors such as therapy and glycosuria affected the results of these tests. This approach, which should extend the usefulness of urinalysis, may prove viable when larger groups, and possibly a different set of tests, are used to establish a more robust combination of tests.

Adult↗

PubMed1992

Ultrasound Doppler spectral analysis in the diagnosis of occlusive lesions of the carotid arteries.

To evaluate the accuracy of Ultrasound Doppler Spectral Analysis (USDA), 432 carotid arteries were examined [group I consisted of 145 cases of normal ICA (internal carotid artery), group II--187 cases of ICA stenosis and group III--100 cases of ICA occlusion]. The maximal systolic peak (Smax), maximal diastolic peak (Dmax), the spectral broadening index (SB) and the pulsativity index (PI) were calculated and related to the degree of stenosis as determined by contrast arteriography. Our results indicate that the change of the value of Smax is the main diagnostic criterion: for carotid arteries' stenoses, it increases to over 3.2 kHz. A Smax over 6.0 kHz is a veritable index of ICA stenosis above 50%: in such cases as the stenosis increases by 10%, this corresponds to an approximately 1 kHz increase of Smax. In ICA occlusion, the main criterion was the absence of blood flow in the distal ICA segment. The UDSA sensitivity in hemodynamically insignificant stenosis is 73.9% which is far higher than in the periorbital Doppler examination; in hemodynamically significant stenosis and ICA occlusions, the sensitivity is 98.6 and 99%, respectively.

Arterial Occlusive Diseases↗

PubMed1977

Local spectral analysis in the visual cortex.

On the basis of experimental evidence presented earlier a model of local spectral analysis of the image performed by the complex receptive fields of the visual cortex has been proposed. An essential feature of the model is that the generalized piece-wise Fourier transform is performed not over the image luminance function but over the logarithm contrast function resulted from analysis of the image by the round receptive fields of the preceding levels. Such an assumption removes a number of experimental objections offered against the hypothesis of two-dimensional Fourier transform in the visual system. The consequences from the piece-wise expansion in a series of basic functions have been considered and among them: the channel frequency characteristics which can have more than one maximum; the possibility of describing the image by a limited number of channels with overlapping frequency characteristics; the existence of mechanisms for estimation of phase shift between frequencies.

Models, Neurological↗

PubMed1976

EEG spectral analysis in children with febrile convulsions.

The abnormal theta-rhythm of the EEG can be identified by use of spectral analysis. The rhythms appear as peaks in the power spectrum and can be considered as given, if the intensity of this peak is significantly higher than the average intensity and if a left-right coherence is present. Abnormal theta-rhythms in the parietal region are significantly more frequent in children with a histroy of febrile convulsions than in controls. This difference becomes especially obvious in the records with open eyes. According to previous investigations, the abnormal theta-rhythm is correlated with a genetically determined susceptibility to convulsions.

Child, Preschool↗

PubMed1977

[Correlation spectral analysis of the spontaneous impulse activity of cerebral cortex neurons].

Spontaneous unit activity in alert unrestrained rabbits was recorded simultaneously with two microelectrodes from the visual and sensorimotor cortex. The correlation analysis revealed that activity of majority of the neurons had no regular rhythm. But spectral analysis of the average correlograms showed existence of oscillations in the delta- and theta-ranges. The synergic type of interaction between cortical neurons was prevalent. Analysis of structure of the distant interaction showed the reduced probability of synergic spikes with periods 150-200 msec and less and the increased one with periods within 200-500 msec.

Animals↗

PubMed1979

Automated detection of EEG artifacts during sleep: preprocessing for all-night spectral analysis.

This paper describes a simple artifact detection algorithm which can be used when large amounts of EEG data are to be automatically processed via spectral analysis techniques in a general purpose digital computer, and visual inspection of each EEG epoch becomes an impossible task. The technique is based on a chi-square (chi(2)) goodness-of-fit test to a Gaussian distribution (CSQ), and it was applied to EEG epochs each 30 sec long. This test proved to be very sensitive to non-stationarities in the EEG amplitude distribution for a particular epoch, and it produced a large value for the chi(2) coefficient when an artifact was present. EEG epochs that gave rise to chi(2) coefficients of value larger than a heuristically determined minimum were discarded from further analysis. The above technique enabled efficient data reduction and reliable automatic off-line processing of 50 nights of sleep EEG via spectral techniques.

Action Potentials↗

PubMed1992

Spectral analysis of the rapid eye movement sleep electroencephalogram in right and left temporal regions: a biological marker of Alzheimer's disease.

Spectral analysis of electroencephalograms (EEGs) for both wakefulness and rapid eye movement (REM) sleep was performed over the temporal regions in 8 patients with mild to moderate Alzheimer's disease and in 8 age-matched control subjects. EEG slowing in Alzheimer patients was found to be much more prominent during REM sleep than during wakefulness. In addition, asymmetry on the awake EEG of Alzheimer patients was found to be even more prominent than on the REM sleep EEG. When EEG values of the most impaired hemisphere during REM sleep were examined, no overlap was found between the two groups either for the ratio of slow to fast frequencies or for percent power of each of the frequency bands. This was not the case for the awake EEG. These results suggest that diagnostically meaningful cutoff values for discriminating patients with mild to moderate Alzheimer's disease from age-matched control subjects can be derived from the REM sleep EEG of the temporal lobe.

Aged↗

PubMedDate not supplied

Imaging the carotid bifurcation using continuous-wave Doppler-shift ultrasound and spectral analysis.

A non-invasive method is described for visualizing the carotid bifurcation using a continuous-wave Doppler-shift technique simultaneously with spectral analysis of the blood velocities from all parts of the vessel lumen. The system is directional so that arteries can be visualized in the presence of signals from adjacent veins. The technique uses a transducer which is attached to a position-sensing arm so that the position of the ultrasound beam on the neck, when sensing arterial blood flow-velocities, can be translated onto a storage oscilloscope. By repeated passes of the transducer across the vessel lumen a 2 dimensional image of the carotid bifurcation is formed. As each image point is marked, the full spectrum of blood-velocities corresponding to that position is continuously displayed on a second oscilloscope beside the image scope. Ultrasound images are compared with arteriograms and both continuous-wave and pulsed Doppler ultrasound imaging systems are discussed.

Adult↗

PubMed1976

A real-time software system on the PDP-11 for two-channel EEG spectral analysis during surgery.

Three functions are performed in real time by a stand-alone PDP-11-assembly language program. First two channels of EEG data are acquired by quantization techniques; second spectral analysis of the EEG data is carried out; third the resulting spectra are displayed as time compressed spectral profiles on an X-Y plotter. The method provides EEG time trends during anesthesia, permitting evaluation of brain functions.

Anesthesia, General↗

PubMed1975

Spectral analysis of the abnormal theta rhythm in the EEG of young children.

The abnormal theta rhythm of the EEG of early childhood was investigated by spectral analysis. The pattern in the power spectrum is characterized by a peak in the thetaband. The relative peak intensity (peak ratio = ratio of peak intensity and average intensity of the spectrum within the frequency range of 0--10 Hz) as well as the right-left coherence proved to be good criteria for the description of the abnormal theta rhythms. When the ratio q greater than or equal to 2.0 and the coherence Coh greater than or equal to 0.7 an abnormal theta rhythm can be considered to be present. When this definition is applied, a high correspondence between the mathematical and visual evaluation of the EEG is present. The abnormal theta rhythm must be regarded as a symptom of a functional anomaly which is -- under electroencephalographic aspects -- characterized by generators acting in abnormal synchronism and monofrequency.

Brain Diseases↗

PubMed1979

Interaction between intermittent photic stimulation and auditory stimulation on the human EEG. Preliminary investigation through power spectral analysis.

The effects of flicker photic stimulation (6, 8, 9, 10, 11, 12, 14, 16 flashes/sec) and of white noise (80 dB SPL) on the EEG of man were investigated with the aid of power spectral analysis. In order to evaluate both the alpha attenuation response (AAR) and the 'driving' reaction induced by flicker as well as the effect of noise, the analysis was carried out on broad (delta, theta, alpha, beta) and on narrow (bandwidth: 1 Hz) spectral bands. A significant correlation between the amount of AAR induced by noise and a measure of the tendency to exhibit photic driving was found, though there was no clear-cut interaction between the photic stimuli and noise when delivered stimultaneously.

Acoustic Stimulation↗

PubMed1977

EEG and haemodialysis. A structural survey of EEG spectral analysis, Hjorth's EEG descriptors, blood variables and psychological data.

Computerized EEG was performed in 20 patients with renal failure before and after haemodialysis (HD), applying spectral analysis and Hjorth's EEG descriptors in EEG quantification, correlation and factor analysis as statistical procedures to analyse the connections of EEG, blood variables and psychological performance. The main results were: (1) Moderate uraemic encephalopathy -- according to Kiley's (1971) standards -- was present in most of our patients, before and after HD. (2) Before HD, EEG slowing was most strongly connected with the creatinine level and EEG acceleration with hyperkalaemia, which in most cases accompanied a high urea level. (3) Significant EEG changes after HD were: decrease of percentage delta activity, increase of Hjorth's 'mobility', decrease of Hjorth's 'complexity'. (4) The theta/alpha ratio (Matousek 1968) was significantly correlated with the patient's general clinical state after HD. (5) Visual discrimination, memory and maximal tapping speed improved significantly after HD. Only Hjorth's EEG parameters were correlated with test performance in that patients with low voltage and fast EEGs did worse in visual discrimination.

Adult↗

PubMed1992

Spectral analysis of cytochromes in rat heart myocytes: transient and steady-state photodiode array spectrophotometry measurements.

Myocytes prepared from rat heart have been studied by optical spectroscopy using a photodiode array spectrophotometer adapted to a stopped flow apparatus (PASF). The isolated cells were viable for 3-4 h (i.e., over the total time of the experiments), as tested employing morphological parameters of cell damage, reactivity toward trypan blue, and the ability to use succinate in the absence and presence of digitonin. Respiration was activated by addition of sodium ascorbate and tetramethyl-para-phenylenediamine (TMPD) as exogenous reductants, in order to single out the contributions of cytochrome c and cytochrome c oxidase among the complexes of the mitochondrial respiratory chain. TMPD was shown to be freely permeable across cytoplasmic and mitochondrial membranes, with a measured KD = 0.9 mM. The use of singular value decomposition analysis coupled to PASF acquisition proved very powerful in resolving statically and kinetically, in the millisecond time region, the spectral contributions of the cytochromes. Spectral analysis was improved by adding carbon monoxide at concentrations which did not affect cytochrome c oxidase activity, but kept myoglobin fully saturated (and thus uninfluential to absorbance changes).

Animals↗

PubMed1977

Lateralisation of speech dominance by spectral analysis of evoked potentials.

A computerised evoked potential test for the lateralisation of speech dominance was compared with the intracarotid sodium amylobarbitone test in 22 epileptic patients. Based on spectral analysis, the computer test correctly predicted the speech dominance of 15 of 16 left speech dominant and five of six right speech dominant patients. This non-invasive test is simple, quick, and innocuous and can be easily implemented on a small laboratory computer.

Adolescent↗

PubMed1979

Spectral analysis of human inspiratory diaphragmatic electromyograms.

The inspiratory diaphragmatic EMG was recorded via esophageal electrodes in six normal subjects. The EMG and ECG signals were analyzed by power density spectral analysis, before and after band-pass filtering (20--1,600 Hz). The EMG spectrum was concentrated in the bandwidth 25--250 Hz. Electrode motion introduced a significant artifact only at low frequencies. The ECG spectrum was also concentrated at lower frequencies, but substantial power from the cardiac signal spilled over across most of the EMG spectrum. Band-pass filtering was therefore effective in minimizing the former but not the latter. Of the various power and frequency parameters used to quantitate the EMG spectrum, the most stable was the centroid frequency. This was reproducible within and between subjects, and was not affected by changing tidal volume or inspiratory flow rate.

Adult↗