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At least 145 records · Page 8Linked to original sources
PubMed1994

Spectral analysis of hemodynamics during infusions of epinephrine and norepinephrine in men.

Spectral analysis of fluctuations in heart rate (HR) and arterial blood pressure (BP) during a 6-h infusion of epinephrine (15 ng.kg-1.min-1) or norepinephrine (30 ng.kg-1.min-1) in 10 normotensive males was used to analyze effects of peripheral sympathetic nervous system activity and adrenal medullary discharge on cardiovascular variability. Power spectra were calculated for each 5-min period for HR, systolic BP, and diastolic BP to yield power values for three frequency bands: low (0.02-0.06 Hz), mid (0.07-0.14 Hz), and high (0.15-0.40 Hz). Infusion of epinephrine and norepinephrine induced plasma concentrations of epinephrine and norepinephrine, respectively, within the high physiological range. Spectral analysis showed that low-frequency fluctuations of BP during infusions of epinephrine and midfrequency fluctuations of BP during infusion of norepinephrine changed in opposite directions. These fluctuations may represent different components of short-term cardiovascular control mechanisms during situations that mimic increased sympathoadrenal activity. No changes were observed in HR fluctuations or high-frequency fluctuations of BP after either catecholamine. Our data imply that changes in concentrations of circulating catecholamines cannot be unequivocally labeled as indexes of an altered sympathoadrenal involvement in short-term cardiovascular control.

Adult↗
PubMed2001

Investigation on diabetic autonomic neuropathy assessed by power spectral analysis of heart rate variability in WBN/Kob rats.

This article investigates the development of cardiovascular autonomic dysfunction caused by diabetes mellitus. We performed power spectral analysis of heart rate variability in WBN/Kob rats as a model of spontaneous diabetes. The heart rate of the rats was measured continuously for 24 hours with an implanted telemetric transmitter, and power spectral analysis of heart rate variability was performed on continuous electrocardiograms. At 4 to 5 months of age, the rats indicated a tendency toward a decrease in plasma insulin concentration without hyperglycemia. At 8 to 9 months of age, they showed remarkable hyperglycemia, loss of the circadian rhythm of the heart rate, and reversion or loss of the circadian rhythm of the blood pressure. By the power spectral analysis of heart rate variability, it became apparent that the circadian rhythm of the low frequency/high frequency ratio was absent even in prediabetic WBN/Kob rats. In addition, the circadian rhythms of the high-frequency power level and low frequency/high frequency ratio were absent in diabetic WBN/Kob rats. These findings indicate that the autonomic nervous system in WBN/Kob rats is progressively damaged from the prediabetic to diabetic state. In conclusion, diabetic autonomic neuropathy may be characterized by the appearance of sympathetic overactivity that precedes the impairment of parasympathetic activity.

Animals↗
PubMed2001

Influence of aging on cardiac baroreflex sensitivity determined non-invasively by power spectral analysis.

Aging reduces cardiac baroreflex sensitivity. Our primary aim in the present study was to assess the effects of aging on cardiac baroreflex sensitivity, as determined by power spectral analysis (alpha index), in a large population of healthy subjects. We also compared the alpha indexes determined by power spectral analysis with cardiac baroreflex sensitivity measured by the phenylephrine method (BS(phen)). We studied 142 subjects (79 males/63 females; age range 9-94 years), who were subdivided into five groups according to percentiles of age (25, 50, 75 and 95). Power spectral analysis yields three alpha indexes: an alpha low-frequency (LF) index of cardiac baroreflex sensitivity that ranges around 0.1 Hz; an alpha high-frequency (HF) index reflecting cardiac baroreflex sensitivity corresponding to the respiratory rate; and alpha total frequency (alpha TF), a new index whose spectral window includes all power in the range 0.03-0.42 Hz. Spectra were recorded during controlled and uncontrolled respiration. Under both conditions, all three alpha indexes were higher in the youngest age group (< or =34 years old) than in the three oldest groups. Notably, alpha TF was significantly higher in younger subjects than in the three oldest groups [14+/-1 ms/mmHg compared with 9+/-1 (P<0.05), 8.1+/-1 (P<0.001) and 8.1+/-1 (P<0.05) ms/mmHg respectively]. BS(phen) showed a similar pattern [12+/-1 ms/mmHg compared with 8+/-0.5 (P<0.001), 6+/-0.5 (P<0.05) and 6+/-1 (P<0.05) ms/mmHg respectively]. No significant differences were found for cardiac baroreflex sensitivity among the three oldest groups. All alpha indexes were correlated inversely with age. The index yielding the closest correlation with BS(phen) was alpha TF (r=0.81, P<0.001). Cardiac baroreflex sensitivity in normotensive individuals declines with age. It falls predominantly in middle age (from approx. 48 years onwards) and remains substantially unchanged thereafter. The elderly subjects we selected for this study probably had greater resistance to cardiovascular disease that is manifested clinically, with preserved cardiac baroreceptor sensitivity.

Adolescent↗
PubMed1995

Spectral analysis of blood pressure and heart rate variability in evaluating cardiovascular regulation. A critical appraisal.

Blood pressure variability includes rhythmic and nonrhythmic fluctuations that, with the use of spectral analysis, appear as clear peaks or broadband power, respectively. This review offers a concise and critical description of the spectral methods most commonly used (fast Fourier transform versus autoregressive modeling, time-varying versus broadband spectral analysis) and an evaluation of their advantages and disadvantages. It also provides insight into the problems that still affect the physiological and clinical interpretations of data provided by spectral analysis of blood pressure and heart rate variability. In particular, the assessment of blood pressure and heart rate spectra aimed at providing indexes of autonomic cardiovascular modulation is discussed. Evidence is given that multivariate models--which allow evaluation of the interactions between changes in blood pressure, heart rate, and other biological signals (such as respiratory activity) in the time or frequency domains--offer a more comprehensive approach to the assessment of cardiovascular regulation than that represented by the separate analysis of fluctuations in blood pressure or heart rate only.

Autonomic Nervous System↗
PubMed1994

Spectral analysis of heart rate variability in evaluation of sympathetic function in elderly subjects.

Plasma concentration of noradrenaline is often used as a measure of sympathetic nervous activity. Recently, the method of spectral analysis of heart rate variability has been introduced to detect autonomic dysfunction. To examine whether spectral analysis of heart rate variability is useful in evaluating sympathetic function, changes in the heart rate variability in the low-frequency spectral band were compared with the change of plasma noradrenaline in response to head-up tilt in elderly hypertensives (n = 13) and diabetics (n = 13). In hypertensive subjects, there was an increase in relative low-frequency power (p = 0.015) and an increase in plasma noradrenaline level (p = 0.040) in response to head-up tilt. Diabetics did not show corresponding changes. There was no change in absolute low-frequency power in either group. It is concluded that spectral analysis of heart rate variability can be useful in evaluating sympathetic function in elderly subjects.

Aged↗
PubMed1985

Differential lateralization for positive and negative emotion in the human brain: EEG spectral analysis.

The present experiment utilized EEG spectral analysis to investigate lateralization for emotional processes in the human brain. In frontal zones, a differential lateralization for positive and negative emotion was observed, with relative left-hemispheric activation (as measured by decreases in alpha abundance) for positive emotions and relative right-hemispheric activation for negative emotions. In parietal zones, a differential lateralization for verbal and spatial processes was observed, with relative left-hemispheric activation for verbal questions and relative right-hemispheric activation for spatial questions. Examination of EEG bands other than alpha (i.e. delta, theta, beta, and total power) suggested that emotional and cognitive processes are further distinguished by different EEG spectral patterns.

Adolescent↗
PubMed1999

[Determination of language dominance using EEG spectral analysis versus the Wada test in temporal epilepsy (right-handed subjects)].

Spectral analysis of the EEG alpha rhythm was studied in nine temporal epileptic right-handed patients in order to predict localization of the speech area. We studied the variation of the spectral power of the alpha rhythm during an activation paradigm previously validated in normal right-handed subjects. Significant alpha power decreases in the left hemisphere during writing with the right hand (as compared to resting) and/or significant alpha power decreases in the right hemisphere during left-hand recognition and classification of cardboard objects (as compared to resting) were considered as consistent with left-hemisphere dominance for language. The results of EEG spectral analysis were compared with those of the Wada test. The left hemisphere was dominant for language according to the Wada test in eight subjects and the right hemisphere in one subject. Six patients had a significant alpha power reduction in the hemisphere concerned during lateralized cognitive tasks, consistent with language localization in the left hemisphere according to the Wada test. The three remaining patients had no significant EEG spectral power variations. A significant decrease of alpha power in the active hemisphere during cerebral activation seems statistically related to left-hemispheric dominance for language in right-handed subjects (hemispheric specialization). However, the localization of the speech area using this electrophysiological method does not appear clinically relevant for a case-by-case decision in individual patients.

Adolescent↗
PubMed2001

Baroreflex and oscillation of heart period at 0.1 Hz studied by alpha-blockade and cross-spectral analysis in healthy humans.

1. Parameters derived from frequency-domain analysis of heart period and blood pressure variability are gaining increasing importance in clinical practice. However, the underlying physiological mechanisms in human subjects are not fully understood. Here we address the question as to whether the low frequency variability (approximately 0.1 Hz) of the heart period may depend on a baroreflex-mediated response to blood pressure oscillations, induced by the alpha-sympathetic drive on the peripheral resistance. 2. Heart period (ECG), finger arterial pressure (Finapres) and respiratory airflow were recorded in eight healthy volunteers in the supine position with metronome respiration at 0.25 Hz. We inhibited the vascular response to the sympathetic vasomotor activity with a peripheral alpha-blocker (urapidil) and maintained mean blood pressure at control levels with angiotensin II. 3. We performed spectral and cross-spectral analysis of heart period (RR) and systolic pressure to quantify the power of low- and high-frequency oscillations, phase shift, coherence and transfer function gain. 4. In control conditions, spectral analysis yielded typical results. In the low-frequency range, cross-spectral analysis showed high coherence (> 0.5) and a negative phase shift (-65.1 +/- 18 deg) between RR and systolic pressure, which indicates a 1-2 s lag in heart period changes in relation to pressure. In the high-frequency region, the phase shift was close to zero, indicating simultaneous fluctuations of RR and systolic pressure. During urapidil + angiotensin II infusion the low-frequency oscillations of both blood pressure and heart period were abolished in five cases. In the remaining three cases they were substantially reduced and lost their typical cross-spectral characteristics. 5. We conclude that in supine rest conditions, the oscillation of RR at low frequency is almost entirely accounted for by a baroreflex mechanism, since it is not produced in the absence of a 0.1 Hz pressure oscillation. 6. The results provide physiological support for the use of non-invasive estimates of the closed-loop baroreflex gain from cross-spectral analysis of blood pressure and heart period variability in the 0.1 Hz range.

Adrenergic alpha-Antagonists↗
PubMed2000

Suggestion difficulty as a hypothesized moderator of the relation between absorption and suggestibility: a new spectral analysis.

Measures of hypnotic suggestibility and absorption were administered to 146 participants in the guise of different experiments. A spectral analysis was performed by correlating the difficulty of individual hypnotic suggestions with the magnitude of the association between suggestions and absorption. Contrary to the two-component model, absorption was not more highly correlated with passing difficult suggestions than easier suggestions. This was confirmed by a meta-analysis of this and other spectral analysis studies. In addition, cross-study correlations revealed that the magnitude of the association between absorption and individual suggestions is highly variable, rendering the two-component model very difficult to test. These findings indicate that discrepant results in previous spectral analyses may have been due to low reliability of associations with individual scale items, as well as the relatively small number of correlations that constitute the raw data of these analyses.

Female↗
PubMed2001

Assessment of 3D proton MR echo-planar spectroscopic imaging using automated spectral analysis.

For many clinical applications of proton MR spectroscopic imaging (MRSI) of the brain, diagnostic assessment is limited by insufficient coverage provided by single- or multislice acquisition methods as well as by the use of volume preselection methods. Additionally, traditional spectral analysis methods may limit the operator to detailed analysis of only a few selected brain regions. It is therefore highly desirable to use a fully 3D approach, combined with spectral analysis procedures that enable automated assessment of 3D metabolite distributions over the whole brain. In this study, a 3D echo-planar MRSI technique has been implemented without volume preselection to provide sufficient spatial resolution with maximum coverage of the brain. Using MRSI acquisitions in normal subjects at 1.5T and a fully automated spectral analysis procedure, an assessment of the resultant spectral quality and the extent of viable data in human brain was carried out. The analysis found that 69% of brain voxels were obtained with acceptable spectral quality at TE = 135 ms, and 52% at TE = 25 ms. Most of the rejected voxels were located near the sinuses or temporal bones and demonstrated poor B0 homogeneity and additional regions were affected by stronger lipid contamination at TE = 25 ms.

Brain↗
PubMed1994

Quantification of the fetal heart rate variability by spectral analysis of fetal well-being and fetal distress.

Our objectives were to increase the discrimination between fetal distress and fetal well-being, using fetal heart rate spectral analysis. Monitoring of the heart rate from 259 fetuses was done between 26 and 42 weeks, interpreted with classical criteria, and analysed with the spectral analysis method we developed. The fetal heart rate spectrum analysis performed on these recordings allow discrimination of fetal distress from the normal state using the energy value and frequency of the maximal energy in the high frequency band. We can conclude that the spectral analysis produces two significant parameters which could contribute to a multivariate approach to assessments of the physiological mechanisms of heart rate variability.

Female↗
PubMed1983

[Spectral analysis of rapid (beta) EEG activity].

Spectral analysis techniques provide high resolution of the beta frequency range and, if a logarithmic transformation is used, also of lower level intensity. This is in contrast to the generally poor resolution of fast activity in the time domain, an effect which may be compared with that of a magnifying glass applied to beta activity. In the frequency domain several different types of beta activity may be distinguished, i.e., (1) narrow; (2) medium; (3) broad-band beta; (4) harmonic beta where the beta component shows a harmonic relationship to a lower frequency component; (5) complex beta as a mixture of 2 or more of the foregoing types; and (6) undefined beta, where the relative increase of beta power is the only assessable feature. If observed, significant coherence occurs most frequently between antero-posterior leads in activities of types 1 and 2, whereas coherence between hemispheres is generally low. Broad-band beta seems to be essentially non-coherent. Coherence of harmonic beta depends largely on the features of the underlying component. Bi-coherence analysis may be of help to further analysis of harmonic or complex beta activity.

Beta Rhythm↗
PubMed1989

Anterior-posterior relationships of EEG in photosensitive subjects: coherence and cross-phase-spectral analysis.

Coherence and cross-phase-spectral analysis of EEG were applied to photo-sensitive subjects to investigate the mechanism of the generalization of photo-induced paroxysms. Coherence values were high between frontal (F) and central (C) in resting records and between F-C in EEGs revealing harmonic responses, where the coherence values of F-O (occipital) were also high, and the waves of F preceded those of O. In cases of occipital-localized 3/6 Hz (poly) spike-waves, discharges of O preceded those of F. During the stage of generalized paroxysms, discharges were highly cohered between all electrodes. Discharges of F preceded those of O, and appeared to play as a generator. Two conditions with clinical symptoms had higher frequencies (greater than or equal to 12 Hz) and shorter time lags (less than or equal to 5 msec) than conditions without symptoms.

Adolescent↗
PubMed1990

Spectral analysis of tremor: understanding the results.

Spectral analysis of a tremor record can sometimes produce a spectrum with multiple components of significant amplitude. The problem is to determine whether the presence of several peaks represents the coexistence of separate tremor mechanisms or be a consequence of fluctuations in the frequency or amplitude of a single tremor. The spectrum of a tremor whose frequency or amplitude vary and are independent has the recognisable pattern of a central carrier frequency with sidebands of equal amplitudes distributed symmetrically around the carrier. However, if tremor amplitude and frequency fluctuate and are not independent, (frequency proportional to amplitude or frequency inversely proportional to amplitude), the spectrum has a pattern of sidebands which are asymmetrical in amplitudes and may resemble the spectrum of the combined signal from different independent oscillators. The investigation of sidebands in spectra has been neglected in tremor studies and multiple irregular peaks on a tremor spectrum have sometimes been used wrongly as evidence for the coexistence of multiple tremor mechanisms or frequency components assumed to be concurrent.

Computer Simulation↗
PubMedDate not supplied

Phonocardiogram spectral analysis simulator of mitral valve prostheses.

Spectral analysis of sounds produced in vitro by mitral valve prostheses placed in a specially designed flow simulator has been carried out using a short-time Fourier representation of the recorded signal. Time variations of power spectra are displayed as a three-dimensional plot. Sounds produced by three types of valves, namely ball and cage, tilting disk and porcine valves, were analysed. Each valve type produced a characteristic spectrogram, and, for a given valve, spectrograms were reproducible to within a margin of 5 dB. The simulator may be used to detect structural deficiencies and functional abnormalities of prosthetic heart valves. In addition to quantifying the noise level of mechanical valves, the system may be used for quality control purposes to identify faulty valves.

Equipment Design↗
PubMed2003

[Spectral analysis of the ECG R-R interval permits early detection of vagal responses to neurosurgical stimuli].

OBJECTIVE: To assess the efficacy of ECG spectral analysis, compared with heart rate (HR) monitoring in the detection of vagal response to surgical stimuli. METHODS: Twenty Asa II-III patients (age: 65 +/- 13 years) scheduled for surgery of cerebellopontine angle or implantation of sacral root stimulator were examined. Target controlled infusion of propofol (2-4 microg x ml(-1)) and remifentanil (4 ng x ml(-1)) was guided by the bispectral index (Bis). Arterial pressure via a radial catheter, pulse oximetry and end tidal CO2 were continuously monitored. Spectral analysis was achieved by connecting a computer to the cardiorespiratory monitor. Online power spectrum densities were calculated from the ECG R-R interval by software based on the fast Fourier transform (LabView, National Instruments, USA). Low frequency (LF: 0.04-0.15Hz) and high frequency (HF: 0.15-0.4Hz) were associated with sympathetic and parasympathetic activities respectively. We defined vagal reaction as a decrease in FC or an increase in HF >10% of the prestimuli value. HF and FC were compared according to the detection delay (by a Student t test with p < 0.05 considered significant) and a concordance test with a kappa coefficient (kappa): -1 = total discordance to 1 = total concordance. RESULTS: Twelve vagal reactions (observed in 8 patients) were detected within 5.5 +/- 1.3 s (HF) and 12.4 +/- 1.6 (FC); p < 0.001. Concordance between the 2 parameters was 95% (kappa =0.9). CONCLUSION: The ECG spectral analysis is a non-invasive technique, which permits the detection of intra-operative vagal reactions earlier than conventional monitoring of HR.

Aged↗
PubMed2005

Multi-site recording and spectral analysis of spontaneous photon emission from human body.

BACKGROUND: In the past years, research on ultraweak photon emission (UPE) from human body has increased for isolated cells and tissues. However, there are only limited data on UPE from the whole body, in particular from the hands. OBJECTIVE: To describe a protocol for the management of subjects that (1) avoids interference with light-induced longterm delayed luminescence, and (2) includes the time slots for recording photon emission. MATERIAL AND METHODS: The protocol was utilised for multi-site recording of 4 subjects at different times of the day and different seasons, and for one subject to complete spectral analysis of emission from different body locations. An especially selected low-noise end-window photomultiplier was utilised for the detection of ultraviolet / visible light (200-650 nm) photon emission. For multi-site recording it was manipulated in three directions in a darkroom with a very low count rate. A series of cut-off filters was used for spectral analysis of UPE. 29 body sites were selected such that the distribution in UPE could be studied as right-left symmetry, dorsal-ventral symmetry, and the ratio between the central body part and extremities. RESULTS: Generally, the fluctuation in photon counts over the body was lower in the morning than in the afternoon. The thorax-abdomen region emitted lowest and most constantly. The upper extremities and the head region emitted most and increasingly over the day. Spectral analysis of low, intermediate and high emission from the superior frontal part of the right leg, the forehead and the palms in the sensitivity range of the photomultiplier showed the major spontaneous emission at 470-570 nm. The central palm area of hand emission showed a larger contribution of the 420-470 nm range in the spectrum of spontaneous emission from the hand in autumn/winter. The spectrum of delayed luminescence from the hand showed major emission in the same range as spontaneous emission. CONCLUSION: Examples of multi-site UPE recordings and spectral analysis revealed individual patterns and dynamics of spontaneous UPE over the body, and spectral differences over the body. The spectral data suggest that measurements might well provide quantitative data on the individual pattern of peroxidative and anti-oxidative processes in vivo. We expect that the measurements provide physiological information that can be useful in clinical examination.

Adult↗
PubMed1997

End-plate electromyography: use of spectral analysis of end-plate noise.

An automated technique for estimating the channel open time of human end-plate acetylcholine receptors (AChR) is described. The method, which is based on the power spectral analysis of electromyographic end-plate noise, is simple and permits a rapid estimation of the dominant AChR ion channel kinetics. Values of AChR channel open time determined by spectral analysis of end-plate noise in adults (1.23 +/- 0.01 ms at 33 degrees C) were consistently shorter than those estimated from the decay phase of extracellularly recorded miniature end-plate potentials. The channel open time extracted from the end-plate noise compared well with that derived from the analysis of in vitro recorded acetylcholine-induced current noise. Therefore, spectral analysis of end-plate noise may provide a good estimation of the kinetics of the human AChR ion channel. The technique is particularly useful in identifying congenital myasthenic syndromes with altered AChR ion channel function.

Adult↗