Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Spectral Analysis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 433 records · Page 24Linked to original sources
PubMed1994

Computing heart rate variability using spectral analysis techniques: HRVUAB, a ready-to-use program.

The application of spectral analysis techniques to study the nervous modulation of the vertebrate heart have given interesting results in clinical studies although nearly nothing is known in lower vertebrates. A program to compute this heart rate variability is described in detail and preliminary results are shown. Data is first statistically qualified and fragmented in smaller segments, each being further processed through linear trend removal and normalization before the application of the Fast Fourier Transform algorithm to estimate the interval spectrum. All consecutive periodograms are averaged and the interval spectrum plotted and saved.

Algorithms↗
PubMed1997

Power spectral analysis of autonomic nervous activity in spontaneously hypertensive rats.

We studied power spectral analysis of heart rate variability (HRV) in control spontaneously hypertensive rats (SHR) and tourmaline hydroxyl negative ion-treated SHR groups. The power spectrum of HRV in SHR groups was composed of two frequency components; low frequency (LF, 0.005 approximately 1.0 Hz) and high frequency (HF, 1.0 approximately 2.0 Hz) components. The low frequency power (LFP) of HRV spectrum, which indicates sympathetic nervous activity, in negative air ion-treated SHR group was significantly (p < 0.01) smaller than in control SHR group. And also we obtained that the high frequency power (HFP) showing parasympathetic nervous activity in negative air ion-treated SHR group was significantly (p < 0.01) higher than in control SHR group. It could be concluded that hydroxyl negative air ions generated by tourmaline ionizer system decreased the elevated blood pressure, and control the sympathetic nervous activity and the parasympathetic nervous activity in SHR having the elevated blood pressure.

Air Ionization↗
PubMed1975

Spectral analysis as a diagnostic aid in the management of high-risk pregnancy.

Spectral analysis of the fetal heart rate and intrauterine pressure was done with data obtained during labor for 24 patients delivered of their infants in an obstetric intensive care unit. The patients were grouped according to clinical assessment of labor and neonatal outcome as normal (11), abnormal/premature (4), and prolonged labor/cesarean section (9). A comparison among groups of spectral density functions and of coherence functions and phase angles failed to reveal consistent features that could be used to distinguish between groups. However, an analysis of the variance (integrated spectrum) and the mean of the base-line component of the fetal heart rate showed that the values for the normal and abnormal/premature groups could be distinguished from the background population. It is suggested that a study of the joint statistics of the variance and the mean may lead to the development of a diagnostic aid to the early detection of incipient fetal distress.

Analysis of Variance↗
PubMed2000

[A computational spectral analysis method for multi-component drugs based on wavelet transform].

A novel computational spectral analysis method for multi-component drugs is proposed. The method applies the wavelet denoise processing technique to principle component regression(PCR). Since noise in the original spectral data is effectively filtered, the performance of PCR is obviously improved. A typical example in multi-component drug analysis has been used to verify the effectiveness of the novel algorithm. Compared with that obtained by PCR, the average of mean relative error which obtained by PCRW decreases to 0.46% from 1.48%.

Algorithms↗
PubMed1990

Spectral analysis on fluctuation of heart period in paralyzed, vagotomized, and unanesthetized decerebrate cats.

Spectral analysis was performed on the heart period fluctuation in vagotomized, paralyzed, and unanesthetized decerebrate cats. The heart period was measured as the time interval between successive R waves of the electrocardiograms. When end-tidal PCO2 was set at the same level as that before immobilization, the power spectral density plot of the heart period fluctuation showed several distinct peaks: one peak corresponded to the frequency of the artificial ventilator and the others to its harmonics. In addition, the spectral density plot had another peak centered at the intrinsic respiratory frequency evaluated by recording efferent phrenic neural discharges. The amplitude of these spectral peaks tended to become greater when the end-tidal PCO2 was increased by adding CO2 to the input gas. Our results, therefore, provide evidence that the heart period is modulated not only by the artificial ventilation rhythm but also by the centrally generated respiratory rhythm, and suggested that the strength of such central interactions between cardiac and respiratory rhythms varies depending on the end-tidal PCO2 level.

Animals↗
PubMed2006

Power spectral analysis of two-channel EEG in hypoxic-ischaemic encephalopathy.

AIMS: Power spectral analysis combined with a two-channel EEG system may be useful in management of newborn term infants at risk of hypoxic-ischaemic encephalopathy (HIE). This pilot study aimed to determine differences in the EEG power spectrum between normal term infants, infants who were at risk of but had not developed HIE, and infants who had developed HIE. DESIGN: Observational. METHODS: EEG recordings from normal term newborn infants and term infants at risk of HIE were analyzed using fast Fourier transforms. EEG total power (TP), TP variance, TP coefficient of variation (TP CV) and spectral edge frequency (SEF) were compared between three groups: control infants (n=15); at-risk infants who had not developed clinically diagnosed HIE (n=4); and at-risk infants who had developed HIE (n=7). RESULTS: Total power was similar in all groups. Variation of TP (variance and CV) was higher (p<0.05) in control infants than in infants at risk of HIE, regardless of whether they had developed HIE. SEF values were similar across all three groups. CONCLUSION: Reduced variation of EEG power is a feature of infants at risk of HIE.

Analysis of Variance↗
PubMed2004

Spectral analysis of 99mTc-HMPAO for estimating cerebral blood flow: a comparison with H2(15)O PET.

Cerebral blood flow (CBF) can be quantified non-invasively using the brain perfusion index (BPI), which is determined using radionuclide angiographic data obtained through the use of technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO). The BPI is generally calculated using graphical analysis (GA). In this study, BPI was measured using spectral analysis (SA), and the usefulness of SA was compared with that of GA. Thirteen patients with various brain diseases and four healthy male volunteers were examined using radionuclide angiography with 99mTc-HMPAO. The BPI was measured for each subject using both SA and GA. In the four healthy volunteers, the BPI was examined at rest and after the intravenous administration of 1 g of acetazolamide (ACZ). An H2(15)O PET examination was also performed in the 13 patients; the BPIS and BPIG values were compared with the CBF measurements obtained using H2(15)O PET (CBFPET). The BPI values obtained by SA (BPIS) (x) and by GA (BPIG) (y) were correlated (y = 0.568x + 0.055, r = 0.901) in the 13 patients and four healthy volunteers at rest, although the BPIG values were underestimated by 36.1 +/- 7.5% (mean +/- SD) compared with the BPIS values. The degree of underestimation tended to increase with increasing BPIS values. The increase in the BPIS was 32.1 +/- 8.0% after the intravenous administration of ACZ, while the increase in BPIG was only 8.1 +/- 2.8%. This discrepancy was considered to be the result of the BPIG values being affected by the first-pass extraction fraction of the tracer. Although both BPIS and BPIG values were significantly correlated with the CBFPET values, the correlation coefficient for BPIS was higher than that for BPIG (BPIS: r = 0.881; BPIG: r = 0.832). These results suggest that SA produces a more reliable BPI for quantifying CBF using 99mTc-HMPAO than the conventional method using GA. The SA method should be especially useful for activation studies involving pharmacological intervention and/or clinical cases with an increased CBF.

Adult↗
PubMed1992

Isotopomer spectral analysis of triglyceride fatty acid synthesis in 3T3-L1 cells.

A new analysis of stable isotope data for biosynthesis reaction, isotopomer spectral analysis (ISA), is demonstrated. ISA is theoretically applicable for polymerization biosynthesis where data are collected using selected ion-monitoring gas chromatography-mass spectrometry. ISA utilizes the discrete spectrum of isotopomer abundances and the multinomial distribution to estimate two key parameters related to the biosynthesis. These parameters are 1) the dilution of the precursor immediately before biosynthesis and 2) the dilution of the newly synthesized product in the sampled compartment. Differentiated 3T3-L1 cells incorporated 2 mM [1,2-13C]acetate into triglyceride palmitate, yielding a spectrum of mass isotopomers of palmitate. The set of equations for the first nine isotopomers were solved for the two parameters using nonlinear regression. We found that precursor dilutions for acetate and glucose were constant over time, whereas the product dilution parameter increased with time, as expected for cells accumulating triglyceride palmitate. Mathematical procedures are presented for calculating 1) the predicted isotopomer fractional abundance values and 2) the correction for atoms other than the tracer atom in the mass ion.

3T3 Cells↗
PubMed1997

Do high proinsulin and C-peptide levels play a role in autonomic nervous dysfunction?: Power spectral analysis in patients with non-insulin-dependent diabetes and nondiabetic subjects.

BACKGROUND: Immunoreactive insulin has been shown to predict the development of parasympathetic autonomic neuropathy. It is possible that constituents of immunoreactive insulin could explain this association. In this cross-sectional study, the relationship of specific insulin, C-peptide, and proinsulin with autonomic nervous dysfunction was evaluated in 57 NIDDM patients and 108 control subjects. METHODS AND RESULTS: The frequency-domain analysis of heart rate variability was determined by using spectral analysis from stationary regions of registrations while the subjects breathed spontaneously in a supine position. Total power was divided into three frequency bands: low (0 to 0.07 Hz), medium (MFP, 0.07 to 0.15 Hz), and high (HFP, 0.15 Hz to 0.50 multiplied by the frequency equal to the mean RR interval). In NIDDM patients, total power, the three frequency bands (P<.001 for each), and the MFP/HFP ratio (P=.016), which expresses sympathovagal balance, were reduced compared with control subjects. Fasting proinsulin (r(s)=-.324, P=.014 for diabetics and r(s)=-.286, P=.003 for control subjects), C-peptide (r(s)=-.492, P<.001 for diabetics and r(s)=-.304, P=.001 for control subjects), and total immunoreactive insulin (r(s)=-.291, P=.028 for diabetics and r(s)=-.228, P=.017 for control subjects) were inversely related to MFP/HFP. For proinsulin and C-peptide the results did not change after controlling for the effects of age, body mass index, and fasting glucose. CONCLUSIONS: Both proinsulin and C-peptide levels were significantly associated with the sympathovagal balance of autonomic nervous function in NIDDM patients and control subjects, but this study cannot determine whether these compounds are directly involved in autonomic nervous dysfunction.

Aged↗
PubMed1984

Application of Taylor's hypothesis to an unsteady convective field for the spectral analysis of turbulence in the aorta.

Two types of unsteadiness must be considered when spectral analysis is applied to unsteady turbulence such as that found in the aorta. Firstly, the statistical properties of the turbulence itself change in time and so the definition of spectral density must be reconsidered. Secondly, the turbulent velocity fluctuations, whether they are steady or unsteady, are carried by an unsteady convective velocity which alters their properties as seen by a stationary observer. In the present study, unsteadiness of turbulence in the latter sense is discussed by applying Taylor's hypothesis of 'frozen turbulence' to turbulence with an unsteady convective velocity. If both a 'frozen' pattern of turbulence and a constant convective velocity are assumed, measured frequency spectra can be easily transformed into wavenumber (spatial) spectra, usually as a trivial part of normalisation. In the case of unsteady turbulence, however, the convection velocity is no longer constant and the conventional method can not be used. A new method of estimating the spatial properties of unsteady turbulence is proposed in which the temporal fluctuations of the turbulent velocity are transformed into spatial fluctuations using a nonlinear transformation based upon the unsteady convective velocity. The transformed data are then Fourier analysed to yield a wavenumber spectrum directly. The proposed method is applied to data obtained in the canine ascending aorta. Spectra calculated by the proposed method differ significantly from those obtained by the conventional method, particularly in the high wavenumber (or frequency) range. This difference is discussed as an 'aliasing' phenomenon that has also been known in steady turbulence.

Animals↗
PubMed1989

Spectral analysis of EEG responses.

The techniques used and the results obtained in a spectral analysis of two specific responses in the human electroencephalogram are presented in this paper. The purposes are to show how the techniques may be applied to the necessarily short lengths of EEG data and to illustrate these techniques and the useful results obtained by relevant examples. The necessary data-processing procedures and precautions for transforming from the time to frequency domain are presented in a tutorial fashion. The importance of augmenting zeros, choice of the most appropriate data window and pretransformation of the data to avoid the combined effects of energy loss and low frequency content biasing caused by windowing is explained. The pros and cons of the tapered-cosine (Tukey) and Kaiser-Bessel windows are illustrated. The usefulness of applying certain statistical tests, which are based on a physical model of the responses, to the harmonic components of the responses is demonstrated. Thus a comparison is made between the features of auditory evoked responses and of the contingent negative variation, and the usefulness of predictive statistical diagnosis in differentiating between subject groups is illustrated by application to normal subjects and Huntington's chorea patients.

Biomedical Engineering↗
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↗
PubMed1985

Power spectral analysis and cortical coupling of EEG for young and old normal adults.

Power spectral analysis and cortical coupling were computed on eyes closed EEG recorded from 80 normal volunteers: 20 females and 20 males aged 25-35 years and 20 females and 20 males aged 55-70 years. Recordings were from Fz, Cz, C3, Pz and Oz areas. The results indicate that with increased age there was a greater uniformity of EEG activity across the brain. Magnitude of EEG power was significantly less variable across recording sites for the old than for the young. In addition, cortical coupling values were reliably higher for the older subjects indicating a greater congruity among EEG patterns. The EEG power and cortical coupling measures were significantly correlated and thus may indicate an underlying mechanism common to both. The results support a theory of decreased central inhibitory function in old age and may reflect an age-related breakdown of functional autonomy of cortical areas. Gender had no significant effect on either EEG power or cortical coupling.

Adult↗
PubMedDate not supplied

Pulsed Doppler spectral analysis of bounded fluid jets.

To test the hypothesis that pulsed Doppler ultrasound spectral properties of bounded fluid jets related to orifice size, in vitro examinations were performed using a hydraulic simulator (standpipe, compliant receiving chamber, and variable round orifice). Orifices of 17.3, 7.9, 4.5 and 2.0 mm2 area resulted in flows of 4.0, 1.7, 1.1 and 0.3 L/min respectively. We interrogated the fluid jet at midchamber (MC) and at the chamber will impact site (IS), and the resulting Doppler shifts were displayed on a spectrum analyzer. For each orifice size, 36 independent observations were made at each interrogation site. At site MC, a characteristic low break frequency (K) was observed in an otherwise flat spectrum. The spectrum from site IS were peaked, with the peak described by center frequency (P), peak amplitude (A), and frequency at which the peak merged with the background (X). As orifice size increased from smallest to largest, monotonic changes in K (1020-440 Hz), P(330-750 Hz), A (8-28 db), and X (840-2660 Hz) were observed. Standard deviation about each mean ranged from 9 to 28%. Orifice shape, receiving chamber viscosity, and standpipe pressure significantly influenced the spectra. These data suggest that quantification of jet flow is possible in vitro using spectral analysis and pulsed Doppler ultrasound.

Humans↗
PubMed1998

Power spectral analysis of variations in heart rate in patients with hyperthyroidism or hypothyroidism.

Power spectral analysis (PSA) of the variation in heart rate is useful in determining the relative activity of the sympathetic and parasympathetic nerves. In this study, PSA was used to investigate the relationship between abnormalities in autonomic nerve function and the presence of thyroid disorders in patients with autoimmune thyroid diseases. The low frequency (LF) or high frequency (HF) components of R-R variations were determined by PSA. The coefficient of variation of the R-R time intervals (CV(R-R)) was positively correlated with HF in healthy subjects. In untreated hyperthyroid patients with Graves' disease, the CV(R-R) and HF values were significantly lower than in healthy controls. Moreover, the LF/HF ratio in patients with untreated Graves' disease was significantly higher, and the LF/HF ratio in hypothyroid patients with Hashimoto's thyroiditis was significantly lower than in healthy controls. A negative correlation was observed between serum levels of free thyroid hormones (FT4 and FT3) and HF in Graves' disease patients. In some hyperthyroid patients, antithyroid drug therapy or beta-blocker administration gradually restored reduced HF values. Present results suggest that relative vagal nerve activity is reduced in hyperthyroid patients and that this reduction is reversible according to the decrease in serum levels of thyroid hormones.

Adrenergic beta-Antagonists↗
PubMed2001

Influences of a relaxation intervention on perceived stress and power spectral analysis of heart rate variability.

This study was designed to determine whether power spectral analysis (PSA) of heart rate variability (HRV) can detect change in autonomic tone following a relaxation intervention called therapeutic touch (TT). Thirty healthy subjects underwent TT by one of three TT practitioners using the steps developed by Krieger and Kunz (The Therapeutic Touch, Prentice-Hall, 1979). Both subjects and TT practitioners were monitored by continuous electrocardiographic monitoring (Holter) before (15 minutes), during, and after (15 minutes) TT was administered. Subjects and TT practitioners completed a visual analogue scale (VAS) of perceived stress before and after TT. Change scores for VAS and PSA of high-frequency/low-frequency (HF/LF) ratios were compared for the 2-minute interval before TT began and the end of TT and the end of the recovery period, using t tests. VAS scores decreased (less stress) from before to after TT for both subjects (p < 0.0005) and TT practitioners (p < 0.0005). Mean HF/LF ratios increased significantly to reflect greater parasympathetic dominance from before TT to the end of treatment for subjects (p = 0.006), but not for TT practitioners. However, further analysis revealed that this change was due to an exaggerated HF/LF response from four outliers (p < 0.0005). Data collected in this study did not reveal differences between these four subjects and the rest of the sample. There were no significant changes in HF/LF ratios from the end of TT to end of recovery for either group. Further research is needed to determine why some subjects may have greater change in autonomic tone in response to relaxation in order to be able to predict who will demonstrate physiologic response to relaxation interventions.

Adult↗
PubMed2003

[Spectral analysis of maorenshen (Actinidia valvata) and its confusable materials].

This article reports the spectral analysis of Maorenshen (Actinidia valvata) and its confusable materials Actinidia chinennsis and Actinidia polygama by fluorescence test, ultraviolet spectrophotometry and fluorescence spectrophotometry. Strong green or blue fluorescence was observed at UV 254 nm in aqueous solutions of Actinidia chinesis and Actinidia polygama, and was barely seen in that of Maorenshen. There were also obvious differences among the ultraviolet spectra and fluorescence spectra of the extracted solutions of the three materials. No obvious absorption band was observed in the UV spectra of ethanol-extracted solution of Maorenshen, an absorption band at 280 nm was observed in the UV spectra of Actinidia chinensis and Actinidia polygama in ethanol extract-solutions. There were also different wavelength and strength in fluorescence spectra among extracted solutions of Maorenshen, Actinidia chinensis and Actinidia polygama. Therefore, it is feasible to identify Maorenshen (Actinidia valvata) and its confusable materials by ultraviolet spectrophotometry and fluorescence spectrophotometry.

Actinidia↗
PubMedDate not supplied

[A spectral analysis of the periodic components in the heart rhythm structure of newborn infants].

Spectral analysis of spontaneous heart rate fluctuations were assessed in 12 healthy newborn infants and in 14 low birth weight newborns. The orthostatic test was performed by the change of newborns posture. High-frequency fluctuations at the respiratory rate were detected in healthy infants and orthostatic reactions of heart rate resembled the same reactions in healthy adults. High-frequency (respiratory) fluctuations were diminished in low-birth weight infants. It is supposed that respiratory fluctuations can be used as a sign of newborn infants well-being and maturation.

Aging↗