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At least 1,279 records · Page 71Linked to original sources
PubMed1987

Limitation of deuterium labelled methoximes as internal standards in the mass spectral analysis of prostaglandins.

A reported method for the preparation of d3-methoxime derivatives as internal standards for prostaglandin assays by gas chromatography-mass spectrometry was evaluated. Sample derivatization resulted in 1.5-86% exchange of the d3-methoxime in a series of prostaglandins. Exchange was minimal when the methoxime was on the 5-membered ring; whereas, acyclic methoximes exhibited extensive exchange. Induced strain energy due to the steric interaction of the hydroxyl group and the C13-C20 alkyl side chain with the gem-dimethoxylamine transition state is offered as an explanation for the unusual stability of PGE2. The use of 18O exchange of the carboxylic acid function is presented as an alternative for the preparation of unavailable labelled eicosanoids.

Deuterium↗
PubMed1981

An assessment of spectral analysis of amphetamine-induced behavior.

Testing of a new radio frequency capacitance field type transducer and power spectrum analysis system for assessment of rat behavior is described. Power spectrum estimates of amphetamine-induced behavior had an orderly relationship with behavior ratings ranging from inactive to intense stereotypy. The effects of thorazine dose-response blocking on amphetamine-induced behavior were linear. Separation between adjacent doses could not be accomplished with a single frequency, but required differential frequency-time period information.

Amphetamine↗
PubMed1984

Spectral analysis of heart sounds: relationships between some physical characteristics and frequency spectra of first and second heart sounds in normals and hypertensives.

Frequency analysis of heart sounds has been gaining recognition as a possible indicator of several heart and valve diseases, although a comprehensive study of normal heart sounds has not been published. Relating the frequency content of normal heart sounds to certain physical characteristics surrounding the generation of these sounds could lead to a valuable diagnostic tool and give a better understanding of the mechanism of heart sounds production. In this study, the first and second heart sounds from seventy-four normal, and seven hypertensive volunteers were recorded, digitized and analysed using a Fast Fourier Transform algorithm. Statistical analysis was used to relate physical characteristics (sex, blood pressure, and body surface area) of the subjects to the frequency content of normal heart sounds and to compare normal and hypertensive heart sounds. Statistical analysis showed that the major concentration of energy, for both first heart sound (S1) and second heart sound (S2), is below 150 Hertz (Hz) which may indicate that both sounds are caused by vibrations within the same structure, possibly the entire heart. However S2 spectra have greater amplitude than S1 spectra above 150 Hz, which may be due to vibrations within the aorta and pulmonary artery. Relationships observed between body surface area, sex, blood pressure, and the frequency content of heart sounds indicate that as heart size increases, the amplitude of the frequency coefficients above 150 Hz decreases. These observations were more identifiable in the S1 spectra than in the S2 spectra, possibly because the S2 higher frequency components may mask subtle changes in the S2 spectra caused by heart size changes. However, when the changes in heart size are significant, as in hypertension or increased body surface area, trends in the S2 spectra can be observed.

Adolescent↗
PubMed1988

Medium term comparison of shock attenuating insoles using a spectral analysis technique.

In view of the current interest in skeletal shock and the damage it could cause, this paper illustrates the value of a new device for measuring shock transients reliably during gait. Four orthotic insoles were tested (Viscolas, PPT, Plastazote and Gait Aid) during walking on a timed oval course at intervals during 1 month using the J.P. Biomechanics Shock Meter. The 'shock factor' for each insole was recorded and the data show that Viscolas and Gait Aid do not appear to deteriorate in use whereas PPT and Plastazote do. Viscolas and PPT perform well; Viscolas is just superior; Plastazote (after 2 days) and Gait Aid both perform poorly. It is suggested that manufacturers should acknowledge the effect of use on the insole properties because this information is of paramount interest to the users of their products.

Adult↗
PubMed1986

Optimization of the determination of RNA nucleotide composition by ultraviolet spectral analysis.

We have optimized the spectrophotometric method for the quantitative analysis of a tetranucleotide mixture (for example an RNA hydrolysate) by carefully choosing the wavelengths and the pH at which the absorbance measurements were made, and estimated the error made on the calculated concentration of each nucleotide. The most convenient method involved the measurement of only four absorbances (at 228 nm at pH 13; 200, 212 and 284 nm at pH 2). If the sensitivity of the spectrophotometer is 0.001 unit absorbance, the absolute error made on the calculated percentage of each nucleotide is lower than 0.33%.

Base Composition↗
PubMed1990

Spectral analysis of sympathetic discharge in decerebrate cats.

To evaluate if the 0.1-Hz low-frequency oscillations of R-R interval are a reflection of rhythmical pattern of discharge of the sympathetic outflow, we analysed in 10 decerebrate cats heart rate and cardiac sympathetic efferent discharge variability. A predominant low-frequency component was present in both signals, thus suggesting that the 0.1-Hz rhythm indeed reflects a rhythmical pattern of discharge of sympathetic outflow.

Animals↗
PubMed1993

Effects of anesthesia on sympathetic nerve rhythm: power spectral analysis.

It has been shown that central transduction of the input from arterial baroreceptors shows bandpass characteristics. Previous studies have demonstrated that anesthesia may affect the gain of arterial baroreflex control of sympathetic nerve activity, but whether anesthesia affects the frequency response of central transduction of the arterial baroreflex system is not known. We examined cardiac cycle-related oscillation of renal sympathetic nerve activity (RNA) in conscious (n = 5) and alpha-chloralose-anesthetized (n = 10) rabbits. Power spectra of arterial pressure and RNA were obtained at rest, after i.v. propranolol and after i.v. isoproterenol. At rest with a cardiac cycle at about 5 Hz, cardiac cycle-related oscillation of RNA was observed in conscious rabbits, but it was not present or markedly attenuated in anesthetized rabbits. As the cardiac cycle was slowed by propranolol in anesthetized rabbits, cardiac cycle-related oscillation of RNA gradually appeared. These results suggest that alpha-chloralose anesthesia in rabbits narrowed the bandpass region of the central baroreflex system so that the baroreceptor input at a high frequency (above 5 Hz) was no longer transduced into RNA.

Animals↗
PubMed1995

Young borderline hypertensives are hyperreactive to mental arithmetic stress: spectral analysis of R-R intervals.

To investigate whether sympathetic tone and its reactivity to stress are increased in borderline hypertension, we compared pressor and autonomic nervous responses to mental arithmetic stress in male borderline hypertensives (BH) and normotensive volunteers (NT). Three age groups, 30, 40 and 50-year-old groups, which included 30 to 39, 40 to 49 and 50 to 59-year-old subjects, were studied. Fractional LF (%LF), fractional HF (%HF) and L/H, obtained from the power spectrum of R-R intervals, were used as indices of autonomic nervous function. Baseline autonomic nervous indices did not differ between NT and BH of any age group. Blood pressure rose higher during mental arithmetic stress in 50 than in 30-year-old NT but not in comparable age groups of BH. Pressor responses were augmented in BH compared to NT only in the 30-year-old group. However, the differences were not significant when pressor responses were expressed as percent increases in blood pressure. Both %L and L/H increased during arithmetic stress. The increase in %L did not differ between NT and BH but that in L/H (% delta L/H) was larger in 50 than in 30-year-old NT. % delta L/H was larger in BH than in NT only in the 30-year-old group. These findings suggest that both pressor and autonomic nervous responses to metal arithmetic stress were altered by aging and augmented in BH compared to NT in the 30-year-old group.

Adult↗
PubMed1989

Multivariate EEG power spectral analysis in acute schizophrenics.

The electroencephalogram (EEG) during information processing is influenced by specific changes in brain electrical activity. Based on the theory of disturbed information processing in schizophrenics, we analysed auditory stimulus induced EEG changes by Fast Fourier Transformation. The most important of the significant stimulation-dependent EEG power changes were measured in the 0.5-3.5 Hz and 10-13.5 Hz frequency bands in the left frontoparietal lead. In a multivariate analysis the separation of the subjects examined into acute schizophrenics and normals was incorrect in only 21% of the cases (resubstitution rate); using pi-method an error of 31% was estimated.

Acoustic Stimulation↗
PubMedDate not supplied

Spectral analysis of EEG in Alzheimer's disease: relation to apolipoprotein E polymorphism.

Apolipoprotein E (ApoE) epsilon 4 allele is a risk factor for late-onset Alzheimer's disease (AD) and proposed to have a direct impact on cholinergic function in AD. Slowing of the EEG is characteristic in AD and the cholinergic system has an important role in modulating EEG. Fifty-eight AD patients at the early stage of the disease and 34 age- and sex-matched controls were studied using the quantitative EEG recorded from T6-O2 derivation. AD patients were divided into two subgroups: a) according to the ApoE allele (2 epsilon, 1 epsilon 4, and 0 epsilon 4) and b) according to familial aggregation. AD subgroups did not differ in clinical severity or duration of dementia. The AD patients with the epsilon 4 allele had higher relative theta amplitude and lower relative beta amplitude than controls and patients without the epsilon 4 allele. The peak frequencies were lower in all AD subgroups compared to controls. In conclusion, we found a tendency towards more pronounced EEG slowing in AD patients carrying the epsilon 4 allele. The minor differences in EEG may suggest differences in the degree of the cholinergic deficit in these subgroups.

Aged↗
PubMed1990

Staircase potentiation in isolated frog skeletal muscle: power spectral analysis of the evoked compound muscle action potential.

1. The mechanical and electrophysiological effects of repetitive, low-frequency electrical stimulation on paired sartorii muscles from small male frogs have been investigated, in vitro. 2. Stimulation for 90 sec at 5 Hz resulted in a progressive rise (staircase) than fall (fatigue) in peak twitch tension. 3. The root mean square amplitude, peak-to-peak amplitude, conduction velocity and mean power frequency of evoked compound muscle action potentials (CMAPs) decreased over the stimulation period. 4. Results suggest that alterations in the shape of the CMAP during repetitive stimulation may contribute to the staircase phenomenon.

Action Potentials↗
PubMed1995

Statistical bias and variance in blood flow estimation by spectral analysis of Doppler signals.

The stochastic nature of the Doppler signal is discussed as a source of variability and bias in estimation of mean blood velocity and flow performed using the Discrete or Fast-Fourier Transform. The estimators studied are those appropriate when the ultrasound beam is assumed to be wide enough to insonate the cross-section of the vessel uniformly, and assumed to be narrow enough to insonate only a diameter. Approximate expressions are derived theoretically for the biases and variances of these statistics when the Doppler power spectrum is uniform. For more complex spectra numerical evaluation is carried out by computer. Results for the double-sided spectra obtained from mixed flow are inferred from the single-sided cases. Typically, an estimate of instantaneous mean velocity has very little bias added (< 1%) but might have a standard error of approximately 10% of its mean value, and an estimate of flow in one cardiac cycle a standard error of approximately 1% of its mean value.

Bias↗