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At least 973 records · Page 54Linked to original sources
PubMed1993

Continuous, on-line, real-time spectral analysis of systemic arterial pressure signals.

We present in this communication an algorithm that offers continuous, on-line, real-time analysis of the power spectrum (CORAPS) of systemic arterial pressure (SAP) signals. Based on direct fast Fourier transform of raw SAP signals into power spectral density, it is suitable for the delineation of acute SAP spectral changes over time after physiological or pharmacological perturbations. Thus it is an improvement over most current methods, which only generate the spectra off-line or from intermittent data. Furthermore, all executions can be accomplished economically with a general-purpose personal computer. We demonstrated and quantified vivid sequential alterations in the low-frequency components (< 3 Hz) of the SAP spectrum, which purportedly reflect the influence of vasomotor, baroreceptor, and respiratory activity on SAP during pentobarbital administration or transient hypertension. Three window options incorporated into the algorithm further improved the frequency or temporal resolution and discrimination of the spectral changes during abrupt hypertension or hypotension. Thus our CORAPS algorithm may be useful as an on-line monitor for acute hemodynamic changes.

Algorithms↗
PubMed2005

Spectral analysis and the dynamic response of complex networks.

The eigenvalues and eigenvectors of the connectivity matrix of complex networks contain information about its topology and its collective behavior. In particular, the spectral density rho(lambda) of this matrix reveals important network characteristics: random networks follow Wigner's semicircular law whereas scale-free networks exhibit a triangular distribution. In this paper we show that the spectral density of hierarchical networks follows a very different pattern, which can be used as a fingerprint of modularity. Of particular importance is the value rho(0), related to the homeostatic response of the network: it is maximum for random and scale-free networks but very small for hierarchical modular networks. It is also large for an actual biological protein-protein interaction network, demonstrating that the current leading model for such networks is not adequate.

Journal Article↗
PubMed1998

Automated spectral analysis III: application to in vivo proton MR spectroscopy and spectroscopic imaging.

An automated method for analysis of in vivo proton magnetic resonance (MR) spectra and reconstruction of metabolite distributions from MR spectroscopic imaging (MRSI) data is described. A parametric spectral model using acquisition specific, a priori information is combined with a wavelet-based, nonparametric characterization of baseline signals. For image reconstruction, the initial fit estimates were additionally modified according to a priori spatial constraints. The automated fitting procedure was applied to four different examples of MRS data obtained at 1.5 T and 4.1 T. For analysis of major metabolites at medium TE values, the method was shown to perform reliably even in the presence of large baseline signals and relatively poor signal-to-noise ratios typical of in vivo proton MRSI. Identification of additional metabolites was also demonstrated for short TE data. Automated formation of metabolite images will greatly facilitate and expand the clinical applications of MR spectroscopic imaging.

Aspartic Acid↗
PubMed1996

Comparison of standard autonomic tests and power spectral analysis in normal adults.

Standard autonomic measures [heart rate response to deep breathing (HR[DB]), systolic blood pressure response to orthostatic load, the 30:15 ratio, and the Valsalva ratio (VR)] and spectral measures of the heart rate (HR) and the arterial blood pressure (ABP) (MF: mid-frequency band at 0.05-0.15 Hz; HF: high-frequency band at 0.15-0.33 Hz) were performed in 50 healthy subjects. The supine HR-HF and the tilt ABP-MF were taken as indicators of parasympathetic and sympathetic outflow, respectively. The transfer function magnitude of HR related to the ABP in the mid-frequency band estimated the baroreflex sensitivity. The HR[DB] and the 30:15 ratio were correlated with the parasympathetic spectral measure, and the VR was, surprisingly, only correlated with the sympathetic spectral measure. Significant baroreflex contribution was only evident for the 30:15 ratio. The spectral HR data were highly correlated with their corresponding spectral data of ABP. These results provide insights into autonomic regulation, but further studies on both basic physiological mechanisms of these methods and their clinical value have to be performed before a broad application can be recommended.

Adult↗
PubMed1975

ESR spectral analysis of the molecular motion of spin labels in lipid bilayers and membranes based on a model in terms of two angular motional parameters and rotational correlation times.

Electron spin resonance (ESR) spectral line shapes are calculated for a nitroxide spin-labeled molecule undergoing rapid restricted rotations (twisting) about its long molecular axis while simultaneously tumbling within a cone. Explicit expressions are derived for the hyperfine splittings and g-values, as well as for the secular contributions to the motionally modulated linewidths. The present model is useful for analyzing the restricted twisting and tumbling motions, and rotational correlation times, of spin-labeled molecules in bilayers. Simulated spectra compare well with experimental spectra of lecithin bilayers marked with cholestane spin label, over a wide temperature range.

Cholestanes↗
PubMed2005

Spectral analysis of protein-protein interactions in Drosophila melanogaster.

Within a case study on the protein-protein interaction network (PIN) of Drosophila melanogaster we investigate the relation between the network's spectral properties and its structural features. The frequencies of loops of any size within the network can be derived from the spectrum; also the prevalence of specific subgraphs as a result of the network's evolutionary history affects its spectrum. The discrete part of the spectral density shows fingerprints of the PIN's topological features including a preference for loop structures. Duplicate nodes are also characteristic for PINs and we discuss their representation in the PIN's spectrum as well as their biological implications.

Animals↗
PubMed2005

Noninvasive estimation of tissue temperature via high-resolution spectral analysis techniques.

We address the noninvasive temperature estimation from pulse-echo radio frequency signals from standard diagnostic ultrasound imaging equipment. In particular, we investigate the use of a high-resolution spectral estimation method for tracking frequency shifts at two or more harmonic frequencies associated with temperature change. The new approach, employing generalized second-order statistics, is shown to produce superior frequency shift estimates when compared to conventional high-resolution spectral estimation methods Seip and Ebbini (1995). Furthermore, temperature estimates from the new algorithm are compared with results from the more commonly used echo shift method described in Simon et al. (1998).

Algorithms↗
PubMed2005

Micro-synthesis and electron ionization mass spectral analysis of O-alkyl N,N-dialkylphosphoramidocyanidates.

This communication describes microsynthesis and GC/MS analysis of O-alkyl N,N-dialkylphosphoramidocyanidates (ADAPCs), which are analogues of chemical warfare agent, Tabun. The study was undertaken with a view to develop spectral data base of ADAPCs for verification purpose of Chemical Weapons Convention (CWC). Reported microsynthetic approach has advantages over traditional synthesis in terms of efficiency, synthetic waste, and exposure to toxic chemicals. GC/MS analysis of variety of these compounds (ADAPCs) was performed. Based on the obtained mass spectra of structurally diverse ADAPCs, the fragmentation routes are proposed, which explains most of the characteristic ions.

Chemical Warfare↗
PubMed1998

Automated spectral analysis II: application of wavelet shrinkage for characterization of non-parameterized signals.

An iterative method for differentiating between known resonances and uncharacterized baseline contributions in MR spectra is described. The method alternates parametric modeling, using a priori knowledge of spectral parameters, with non-parametric characterization of remaining signal components, using wavelet shrinkage and denoising. Rapid convergence of the iterative method is demonstrated, and examples are shown for analysis of simulated data and an in vivo 1H spectrum from the brain. Results show good separation between metabolite signals and strong baseline contributions.

Algorithms↗
PubMed1982

A critical study of ultrasound Doppler spectral analysis for detecting carotid disease.

The results of in vitro and in vivo studies to determine the application and limitations of frequency analysis for CW Doppler ultrasound assessment of carotid stenoses are reported. In the in vitro study, the peak Doppler frequency and a new spectral broadening index were determined proximal to, at, and distal to axisymmetric and asymmetrical model stenoses. Good correlations with percent area stenoses were found. In the clinical study, 162 cases were examined using a 4 MHz Doppler system and by standard four-vessel arteriography. Peak frequencies of greater than 3.8 KHz were diagnostic of internal carotid stenoses of 3.2 mm minimum lumen diameter or less, with a sensitivity of 92% and a specificity of 94%. Spectral broadening, evaluated by subjective grading, yielded similar results.

Carotid Artery Diseases↗
PubMed2006

[MOA spectral analysis of additive element contents in lube oil].

The determination of the additive contents of marine lubrication oil by using atomic emission spectrometry is described. A new measuring method is suggested in accordance with the working principle of MOA atomic emission spectral instrument. The additive element contents, if not within the precision limits of MOA atomic emission spectra, are to be measured by being diluted with a standard oil. Error analysis is conducted and the calibration curve method is used. The testing result indicates that the RSD of Ca, P and Zn is 1.6%, 4.8% and 4.6% respectively, and the error result of oil sample before and after diluting is 4.21%, 6.99% and 5.09% respectively.

English Abstract↗
PubMed1988

Preparation of a one-subunit cytochrome oxidase from Paracoccus denitrificans: spectral analysis and enzymatic activity.

Cytochrome c oxidase was isolated from Paracoccus denitrificans as a two-subunit enzyme. Chymotrypsin-catalyzed proteolysis reduced the molecular weight of each subunit by about 8000. The spectral properties of this preparation, as well as its Km for cytochrome c(1.7 muM), remained unchanged with respect to the native enzyme. Vmax was reduced by about 55% when assayed in Triton X-100 or in Triton X-100 supplemented with asolectin. Following further proteolysis by Staphylococcus aureus V8 protease, subunit I remained unchanged as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, whereas subunit II was split into small peptides. These were removed by ion-exchange high-performance liquid chromatography. The one-subunit enzyme had an apparent molecular weight of 43,000. The reduction of molecular weight was also confirmed by the diminution of the ultraviolet/Soret absorption ratio. This value was 1.8-2.1 for the native enzyme and 1.3-1.5 for the one-subunit enzyme. The spectral properties (including the spectrum CO reduced minus reduced) were not modified by the proteolytic treatment, indicating that cytochromes a and a3 were present in equal amounts. The lack of spectral alteration and the known close association of the copper B atom with cytochrome a3 suggest that copper B is also contained within the one-subunit enzyme. The Km of the one-subunit oxidase was similar to that of the two-subunit enzyme; Vmax was decreased by about 50%. The activity of the one-subunit oxidase had a salt-dependent maximum at 30 mM KCl, almost identical with that of the undigested enzyme, and was inhibited by micromolar concentrations of KCN.

Affinity Labels↗
PubMed1999

Spectral analysis of periodic fluctuations in electrocardiographic repolarization.

Repolarization alternans (RPA) indicates alternate-beat fluctuations in the temporal or spatial characteristics of the echocardiogram (ECG) STU segment which may represent dispersion in repolarization. Spectral decomposition has revealed microvolt-level RPA which has been found to correlate with ventricular tachycardia (VT) and fibrillation, and is increasingly being used for clinical risk stratification. However, while interruptions in periodicity are known to affect spectral decomposition, their quantitative impact on RPA and its clinical utility have been poorly described. We therefore studied the effect of variable alignment, extrasystoles, dissimilar beats and beat exclusion on RPA magnitude in simulations and on the sensitivity and specificity of RPA for VT in a pilot clinical study. RPA magnitude was exquisitely sensitive to QRS alignment such that +/- 1 ms random beat misalignment reduced it by 68% in simulations. Correspondingly, suboptimal QRS alignment in clinical ECG's caused the sensitivity of RPA for inducible VT to fall from 93% to as low as 63%; while JT alignment was also less effective for RPA recovery. As an experiment in minimizing morphometric irregularities in clinical ECG's, we found that RPA magnitude actually fell when replacing either measurably dissimilar or ectopic beats with more representative beats. In addition, inserting or deleting beats also reduced RPA magnitude in clinical sequences and simulations. These statistical analyses suggest that the precision of beat alignment and interruptions to ECG periodicity, which may occur physiologically, may greatly reduce the clinical utility of RPA for VT. Dynamic alterations in RPA in response to sequence irregularities require further study before RPA may be optimally applied to screen for ventricular arrhythmias.

Chi-Square Distribution↗
PubMed1993

On-line recognition and quantitation of coeluting hypoxanthine and guanine in reversed-phase high-performance liquid chromatography of placental tissue extracts: photodiode-array detection and spectral analysis of coeluting peaks.

In a reversed-phase HPLC method, optimized for resolution and quantitation of nucleosides and nucleobases in human term placental extracts, guanine coeluted with hypoxanthine. Three numerical techniques that treat spectral data generated by photodiode-array detection to yield indices of peak purity were compared for sensitivity of on-line recognition of overlapped guanine and hypoxanthine peaks in chromatograms of 7.0 microM hypoxanthine containing 0.075-0.54 microM guanine. These techniques were purity parameter, the average wavelength of a peak spectrum (lambda w), peak area ratio, and peak absorbance ratio. Purity parameter of a 7.0 microM hypoxanthine peak containing 1% guanine was significantly different from that of pure hypoxanthine (P < 0.01); peak area and peak absorption ratios were four and seven times, respectively, less sensitive than purity parameter. In chromatograms of human term placental extracts, purity parameter values generated on-line signalled the presence of guanine in hypoxanthine peaks. Quantitation of coeluting hypoxanthine and guanine was performed on-line from dual-wavelength detection at 249 and 278 nm via calibration curves for both analytes at these wavelengths. Hypoxanthine and guanine concentrations in seven samples from five human term placentas were 41-161 and 3-76 nmol/g, respectively. These findings demonstrate that on-line signalling of hypoxanthine and guanine coelution is achieved by purity parameter, area ratio, and absorbance ratio, that purity parameter is the most sensitive index of coelution, and that quantitation of the coeluting analytes can be performed on-line. These approaches should be applicable to recognition and quantitation of coeluting analytes in chromatograms of mixtures of nucleosides and nucleobases such as occur in extracts of other tissues.

Chromatography, High Pressure Liquid↗
PubMed1993

Spectral analysis of the EEG and 99m-Tc-HMPAO SPECT-scan in Alzheimer's disease.

99m-technetium-hexamethylpropylene-amineoxine (99m-Tc-HMPAO) single-photon-emission-computer-tomography (SPECT)-scans and spectral analyzed electroencephalogram (EEGs) of 20 patients with Alzheimer's disease (AD) were studied. A significant correlation was found between the temporoparietal-cerebellar-ratio (TP/C-ratio) of the SPECT-scan and the peak frequencies of leads T3-T5, C3-P3, and C4-P4 of the EEG. In addition a significant negative correlation between the TP/C-ratio and the theta/alpha-ratio (t/a-ratio) of leads T3-T5, T4-T6, C3-P3, and C4-P4 was demonstrated. Our study demonstrates that slowing of the EEG parallels a decrease in blood flow in the temporoparietal regions in AD-patients. Both findings could be parallel phenomena of regional hypometabolism.

Adult↗
PubMed2004

Spectral analysis of burst periods in EEG from healthy and post-asphyctic full-term neonates.

OBJECTIVE: To investigate whether the periodic EEG patterns seen in healthy and sick full term neonates (trace alternant and burst suppression, respectively) have different frequency characteristics. METHODS: Burst episodes were selected from the EEGs of 9 healthy and 9 post-asphyctic full-term neonates and subjected to power spectrum analysis. Powers in two bands were estimated; 0-4 and 4-30 Hz, designated low- and high-frequency activity, respectively (LFA, HFA). The spectral edge frequency (SEF) was also assessed. RESULTS: In bursts, the LFA power was lower in periods of burst suppression as compared to those of trace alternant. The parameter that best discriminated between the groups was the relative amount of low- and high-frequency activity. The SEF parameter had a low sensitivity to the group differences. In healthy neonates, the LFA power was higher over the posterior right as compared to the posterior left region. CONCLUSIONS: Spectral power of low frequencies differs significantly between the burst episodes of healthy and sick neonates. SIGNIFICANCE: These results can be used when monitoring cerebral function in neonates.

Asphyxia Neonatorum↗
PubMed1989

A real-time system for the spectral analysis of the EEG.

We have developed an inexpensive and portable system for processing multiple channels of electroencephalograms (EEG) in real-time to assist the electroencephalographer in identifying subtle changes in these data, particularly in the interpretation of long records. Up to 16 channels of data are spectrally decomposed with a selection of bandwidth, windows, scaling methods, epoch averaging, and smoothing options available. The resulting power spectral estimate may be displayed or printed in a variety of formats, including color encoding of selectable spectral bands. Both the sampled EEG and its spectra may be stored for off-line reprocessing, for archiving, or for statistical analysis in the time or frequency domains.

Analog-Digital Conversion↗
PubMed1986

Rhythm of sounds produced by larvae of the oriental hornet Vespa orientalis: spectral analysis.

In the hornet nest of the species Vespa orientalis, there is transmission of information by acoustic means between the larvae and the adults. The rhythmic pattern of the sounds produced by the larvae was recorded and spectrally analyzed for rhythm frequencies by use of the Fast Fourier Transform. The frequency of the "larval activity duration till cessation" was 0.018 Hz whereas the interval between two successive sound productions ranged from 0 to 1.0 Hz. The possible significance of precise signaling by the larvae towards efficient communication in colonies of social insects is discussed.

Animals↗