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PubMed1992

A nonstationarity test for the spectral analysis of physiological time series with an application to respiratory sinus arrhythmia.

The spectral analysis of time series requires the signal to be at least weakly stationary; i.e., the mean, (co-) variance, and spectrum of the time series should not vary from segment to segment. It is commonly assumed that psychophysiological time series are not stationary. This study introduces a nonstationarity test to the psychophysiological literature, which is derived from evolutionary spectral analysis. Basically, the test consists of a double window technique in both the time and frequency domains, leading to a two-way analysis of variance for times and frequencies. In the current study, the nonstationarity test is applied to heart rate data obtained in a typical psychophysiological setting. Heart rate and respiration were measured in four age groups under four conditions--rest, paced breathing, vigilance, and reaction time. The results indicate that only few physiological time series were completely stationary. However, for every subject, and in every condition stationary stretches could be found that were long enough to apply spectral analysis. Spectral measures (power, coherence, and phase spectra) were then compared for stationary parts of the data and the total data. This comparison indicated that nonstationarity affects all spectral measures. Most importantly, Stationarity x Task Condition x Frequency Band interactions were observed for coherence and phase spectra, and there were significant interactions with age for each of the spectral indices. These findings suggest that nonstationarity may result in biased outcomes of significance tests of the effects of task manipulations on the spectral indices of cardiac time series. Thus, it was concluded that the stationarity test should be routinely applied in the spectral analysis of physiological time series. In addition, it was suggested that the nonstationarity test has an even wider range of application that might be of interest to the psychophysiologist.

Adult↗
PubMed1985

The contribution of spectral analysis to the diagnosis of carotid artery disease.

Pulsed and continuous-wave Doppler examinations with spectral analysis were performed on 258 carotid arteries in 220 patients and compared with multiplane contrast angiography. Each artery was examined for stenosis and assigned to one of four groups: normal to 19%, 20% to 49%, 50% to 99%, and occlusion. The incidence of disease was 70%. Diagnostic sensitivity with all noninvasive techniques varied from 76% to 90% depending on the degree of stenosis, with an overall accuracy rate of 86%. In an attempt to evaluate the diagnostic contribution of spectral analysis, stenosis classification by peak frequency alone was compared with that of the full laboratory profile, including spectral analysis. In the 147 carotid arteries in which such data were available, diagnostic sensitivity was improved with spectral analysis by 8% to 29% depending on the degree of stenosis. Detection of occlusions was unchanged. The major contribution of spectral analysis was in detecting non-flow-limiting stenoses of 20% to 49%. Spectral analysis added little to the diagnostic ability of peak frequency to detect lesions with greater than 50% stenosis. Spectral analysis of either pulsed Doppler or continuous-wave Doppler signals is an accurate noninvasive method for evaluating carotid bifurcation disease, which particularly improves the detection of non-flow-limiting stenoses.

Arterial Occlusive Diseases↗
PubMed2006

Tutorial on univariate autoregressive spectral analysis.

In the present paper, the theoretical basis of autoregressive (AR) modelling in spectral analysis is explained in simple terms. Spectral analysis gives information about the frequency content and sources of variation in a time series. The AR method is an alternative to discrete Fourier transform, and the method of choice for high-resolution spectral estimation of a short time series. In biomedical engineering, AR modelling is used especially in the spectral analysis of heart rate variability and electroencephalogram tracings. In AR modelling, each value of a time series is regressed on its past values. The number of past values used is called the model order. An AR model or process may be used in either process synthesis or process analysis, each of which can be regarded as a filter. The AR analysis filter divides the time series into two additive components, the predictable time series and the prediction error sequence. When the prediction error sequence has been separated from the modelled time series, the AR model can be inverted, and the prediction error sequence can be regarded as an input and the measured time series as an output to the AR synthesis filter. When a time series passes through a filter, its amplitudes of frequencies are rescaled. The properties of the AR synthesis filter are used to determine the amplitude and frequency of the different components of a time series. Heart rate variability data are here used to illustrate the method of AR spectral analysis. Some basic definitions of discrete-time signals, necessary for understanding of the content of the paper, are also presented.

Heart Rate↗
PubMed1985

Detection of a fundamental modular format common to transfer and ribosomal RNAs: second-order spectral analysis.

Second-order spectral analysis is used to detect rigorously and to characterize the principal periodicities in the positions of conserved sequences common to tRNAs and rRNAs. It is shown that the shared periodicity having the largest spectral amplitude is 9, followed by 8 and 10, thus forming a closed triad of significant multiplets centered at 9 bases. This conclusion is proposed to reflect a closed triadic set of fundamental tandem repeat lengths in a class of ancestral macromolecules possessing a restricted sequence symmetry. The terms "remanent" and "archeomodular" are used to describe a relic modular format, traces of which are shown here to persist despite the changes that have occurred in the primary structures of ribonucleic acids during the course of their evolution.

Animals↗
PubMed1990

[A power spectral analysis of the EEG in the newborns. II. The power spectral changes of the infants with neonatal asphyxia].

Power spectral analysis of the EEG at the neonatal period was performed in 33 babies with an Apgar score of 6 or less 1 minute after delivery. Their gestational ages ranged from 27 to 40 weeks, and birth weight from 1,013 g to 4,416 g. They were followed up until 18 months of age. All EEGs were recorded when the babies reached to 37-41 weeks of conceptional age, and analyzed using fast Fourier transformation. The percent power in active sleep was evaluated in this study. The abnormal EEG patterns in infants with neurological damage was classified into the following groups: (1) Increase of the percent power of the delta 1 band, (2) Decrease of the percent of the power of the delta 1. On the other hand, the EEG patterns at the neonatal period in infants with normal development who suffered from neonatal asphyxia were similar to those of age-matched controls. These results suggest one of the most important factors deciding the prognosis of the brain damage is the presence of a normal percent pattern. In conclusion, power spectral analysis of EEG at the neonatal period is useful in predicting the outcome of brain damage if it is used with visual inspection.

Asphyxia Neonatorum↗
PubMed1995

[Autonomic nervous activity at episodes of myocardial ischemia in patients with coronary artery disease by heart rate power spectral analysis].

Heart rate power spectral analysis in 44 patients with coronary artery disease was obtained from 24-hour dynamic electrocardiogram. 195 episodes of transient myocardial ischemia that was defined as horizontal or down sloping depression of the ST segment of > or = 0.1 mV and lasted for > or = 2 minutes were studied. The area of low frequency components (LF, 0.02-0.10 Hz) representing predominontly sympathetic tone with some contribution from the parasympathetic tone and that of high frequency components (HF, 0.15-0.40 Hz) representing mainly parasympathetic tone and the value of LF/HF on 4 minute heart rate power spectral graph at the deepest depression of ST segment were compared with that before the episode of myocardial ischemia. The area of HF of fast rate myocardial ischemia occurring in night reduces significantly (P < 0.001), the value of LF/HF increases markedly (P < 0.05) and the area of LF increases slightly. The results suggest that there is a change of autonomic nervous activity during the episode of fast rate myocardial ischemia in night, parasympathetic nervous tone decreases markedly, there may be secondary increase of sympathetic nervous activity.

Adult↗
PubMed2002

Renal uptake rate measurement of 99m Tc-dimercaptosuccinic acid using spectral analysis.

We developed a new method for measuring the rate of renal uptake of 99mTc-dimercaptosuccinic acid (DMSA) using spectral analysis. The renal uptake rate (per minute) of DMSA (K) was calculated by averaging the tissue impulse response function values obtained by spectral analysis between 10 min and 15 min. The K values obtained by spectral analysis correlated well with the renal uptake rates (%) measured 2h after DMSA administration (r=0.921 with background correction; r=0.924 without background correction). There was a good agreement between the K values obtained by spectral analysis using the kidney time-activity curves with (x) and without (y) background correction (r=0.993, y=1.089x+0.004), suggesting that our method requires no background correction. There was excellent correlation between the K values obtained by spectral analysis using the kidney time-activity curves with (y) and without (x) kidney depth correction (r=0.992, y=1.721x+0.000 with background correction; r=0.990, y=1.720x+0.000 without background correction), suggesting that our method requires no kidney depth correction. These results indicate that spectral analysis is appropriate and useful for the quantification of renal uptake rate of DMSA. We believe that this method will facilitate even more widespread utilization of the quantitative assessment of DMSA uptake by planar scintigraphy, since it needs only 10-15 min for imaging, and background and kidney depth correction and blood sampling are not required.

Female↗
PubMed1981

Spectral analysis of the EEG: comparison of various spectral parameters.

One of the main problems in spectral analysis of the EEG consists of finding relevant parameters which are capable of summarizing all information included in the power spectrum. The mathematical properties and the clinical applicability of 4 sets of parameters were compared: (1) percentage of power within the conventional frequency ranges, (2) mobility and complexity (Hjorth), (3) the slope parameter (Dumermuth), (4) the coefficients of the autoregressive model. They were applied to the EEG changes in a child with brain stem tumour during cerebral radiotherapy. The statistical analysis suggests: (I) there are only minor differences in describing the EEG course between the conventional frequency ranges, mobility and the slope parameter, (II) the complexity is less satisfactory, (III) the first autoregressive coefficient of the AR model yields the best results.

Brain Neoplasms↗
PubMed1976

Applications of spectral analysis in medical ultrasonography.

Spectral analysis of ultrasonic reflections from biological tissues can be used to determine basic tissue parameters for use in differential diagnosis. This paper describes the use of the technique under circumstances encountered in several types of clinical examinations. The applications are illustrated with results obtained from laboratory measurements with a system now being employed in a clinical evaluation programme. The test objects studied simulate tissues with planar boundaries, tissues with heterogeneous interior structure, and tissues causing acoustic 'shadowing' of posterior regions.

Animals↗
PubMed1990

Adaptive spectral analysis of cutaneous electrogastric signals using autoregressive moving average modelling.

The recording of the human gastric myoelectrical activity by means of cutaneous electrodes is called electrogastrography (EGG). It provides a noninvasive method of studying electrogastric behaviour. The normal frequency of the gastric signal is about 0.05 Hz. However, sudden changes of its frequency have been observed and are generally considered to be related to gastric motility disorders. Thus, spectral analysis, especially online spectral analysis, can serve as a valuable tool for practical purposes. The paper presents a new method of the adaptive spectral analysis of cutaneous electrogastric signals using autoregressive moving average (ARMA) modelling. It is based on an adaptive ARMA filter and provides both time and frequency information of the signal. Its performance is investigated in comparison with the conventional FFT-based periodogram method. Its properties in tracking time-varying instantaneous frequencies are shown. Its applications to the running spectral analysis of cutaneous electrogastric signals are presented. The proposed adaptive ARMA spectral analysis method is easy to implement and is efficient in computations. The results presented in the paper show that this new method provides a better performance and is very useful for the online monitoring of cutaneous electrogastric signals.

Electromyography↗
PubMed2003

Effect of donepezil on EEG spectral analysis in Alzheimer's disease.

EEG spectral analysis allows a quantitative analysis of changes in the frequency bands during disease progression in Alzheimer's disease (AD) and could be used to monitor treatment and disease progression. Eighteen patients with probable AD were evaluated by Folstein Mini Mental State Examination (MMSE) and EEG spectral analysis before donepezil treatment, 2 months after 5 mg/day and 4 months after the dose was raised to 10 mg/day. EEG evaluations were done in 4 derivations (T3-T5, T4-T6, C3-P3, C4-P4). Six months after treatment there was a significant reduction in the temporal delta amplitudes and an increase in the amplitudes of all the other frequency ranges including theta amplitudes both in the temporal and centroparietal derivations. MMSE scores increased during treatment but the change was not significant. These findings show that donepezil exerts a positive effect on EEG in AD by decreasing delta activity and increasing alpha and beta activity. The increase in theta activity after treatment may reflect a therapeutic shift of delta activity to theta activity.

Aged↗
PubMed1987

Intraoperative assessment of renal and visceral artery reconstruction: the role of duplex scanning and spectral analysis.

To refine our ability to assess intraoperatively renal and visceral reconstructions, we have investigated the usefulness of combined duplex scanning and Doppler spectral analysis to determine the technical adequacy and flow characteristics of these repairs. We studied 62 patients (116 arteries) who underwent renal (83 arteries) or visceral (13) reconstruction by transaortic endarterectomy (76), autogenous graft (12) or prosthetic (5) bypass, reimplantation (2), and dilation (1). Twenty-six nonreconstructed vessels were also studied, including preoperative arteries (6), unrepaired arteries (14), and normal renal arteries (donor nephrectomies) (6). Duplex scanning was performed by means of a 7.5 or 10 MHz probe placed in a sterile glove and plastic sleeve. Peak (Vs) and mean (Vm) velocities measured in meters per second were subsequently calculated from frequency spectral analysis. Spectral broadening (SB) and aortic inflow data were also collected and analyzed. There were no complications related to ultrasound scanning. Mean scan time was 7.8 minutes. Fourteen of 26 nonreconstructed vessels (54%) appeared normal by duplex scanning, including all six control (normal) renal arteries. Sixty-five reconstructed arteries (68%) appeared normal, 27 had various minor defects, and four had major defects (three occlusions and one floating thrombus). The major defects were repaired, whereas minor ones were not. Confirmatory studies were obtained in 19 (73%) nonoperated and 73 (76%) operated vessels. There were two false negative duplex studies (sensitivity 89%) and 17 false positive duplex studies--all minor defects (specificity 77%). The predictive value of duplex scans in detecting the presence of confirmed defects was Tau = 0.47 (p = 0.01). Although SB correlated with B-mode imaging alone (Tau = 0.21, p = 0.07), it added no independent value in predicting the results of a confirmatory study. No other variable (Vs, Vm, or aortic inflow) added to the duplex scan in predicting an abnormal confirmatory study. Detailed renal and visceral artery spectral analysis data are provided for validation of this technique and comparison with transcutaneous studies. These data suggest that the requirement for reliable and immediate assessment of renal and visceral reconstructions, particularly those involving transaortic extraction endarterectomy, is satisfied by duplex scanning.

Endarterectomy↗
PubMed1990

Effect of stimulus parameters on auditory brainstem response spectral analysis.

A recent increase of interest in spectral analysis has been prompted by the suggestion that spectral components of the ABR may contribute to differential diagnosis. Knowledge of the effects of stimulus parameters on the spectral content of the ABR is essential. The present study examined the effect of intensity, rate, and polarity on the spectral content of ABRs of 15 normal-hearing subjects. The effects of intensity were significant at all spectral frequencies examined while the effects of rate and polarity were frequency specific. These results indicate that the effects of stimulus parameters must be considered in examining the ABR spectral analysis.

Acoustic Stimulation↗
PubMed1977

Spectral analysis of Doppler ultrasonic decompression data.

Several aspects of spectral analysis of bubble transients in Doppler ultrasonic decompression data are discussed. The computation of energy density spectra, using fast Fourier transform techniques for analyzing bubble transients, is described. Spectral analysis of data from probes implanted within animals, using a conventional Fourier analyzer, provided good visual indications of bubble events and interesting changes in spectral structure. A new transient spectral analysis technique that is suitable for quantitative real-time monitoring of small decompression bubbles is described. In a feasibility study using data from an implanted probe, an increase of 900% in bubble signal/noise ratio was observed.

Animals↗
PubMed1993

Sound spectral analysis of prosthetic valvular clicks for diagnosis of thrombosed Björk-Shiley tilting standard disc valve prostheses.

To evaluate clinical usefulness of sound spectral analysis in the early detection of prosthetic thrombosis, we analyzed specific patterns of thrombus formation in Björk-Shiley tilting standard disc prostheses in relation to the sound spectral analysis of their click sounds. Among a total of 365 Björk-Shiley tilting standard disc prostheses, nine became thrombotic. These consisted of seven prostheses in the mitral position and two in the aortic position, and the affected valves were replaced in all cases. The sound spectral analysis system includes a wide-frequency microphone and a sound spectral analyzer. To quantify the amplitude of the metallic clicks that are specific to the prosthetic valve sounds, we used a normalized maximal frequency as a diagnostic parameter for valve thrombosis. Thrombus formation was localized at the minor strut in two cases, and these demonstrated abnormally low normalized maximal frequency values only on opening clicks. In four cases thrombus formations were noted at both minor and major struts, and these showed abnormally low normalized maximal frequency values on both opening and closing clicks. In two cases with pannus formation, no abnormalities were found by sound spectral analysis. In one case, which had demonstrated abnormally decreased normalized maximal frequency values of both opening and closing clicks, the normalized maximal frequency values were normalized after thrombolytic therapy, suggesting resolved thrombosis. Reoperation, which was performed for concomitant complication of perivalvular leak, revealed no noticeable thrombus formation. The thrombi were seen on the minor strut during surgical procedures in all cases in which valve thrombosis was indicated by the sound spectral analysis. Therefore, the minor strut is considered to be the prevalent area of thrombus formation, and diagnosis could be made after observation of abnormally low normalized maximal frequency on opening clicks. We found the sound spectral analysis to be an extremely useful diagnostic tool for early detection of thrombosis in the Björk-Shiley tilting standard disc prostheses, especially because the opening clicks of the tilting disc valve were too low in amplitude for auscultation to detect the existence of mild abnormality.

Adolescent↗
PubMed2001

[Parameters of power spectral analysis of heart rate variability for use in clinical evaluation of various stages of diabetic cardiovascular autonomic neuropathy].

UNLABELLED: The aim of the study was to select parameters of power spectral analysis appropriate for clinical evaluation of various degrees of diabetic cardiovascular autonomic neuropathy. The diagnosis of autonomic neuropathy was based on Ewing's battery of cardiovascular autonomic function tests and on short-term power spectral analysis of heart rate variability during a modified orthostatic load (in positions supine-standing-supine). 52 diabetic patients and 24 age-matched controls were included. Diabetic patients were divided into two groups according to the total Ewing score. Groups of 14 subjects with early autonomic neuropathy and 38 subjects with severe AN were comparable in age and diabetes duration. RESULTS: Cumulative spectral power of the total frequency band in all three positions (Total Power LFHF 1 + 2 + 3) proved to be the most selective and discriminating parameter of power spectral analysis between the control group and diabetic patients with severe autonomic neuropathy in stepwise discriminant analysis. Spectral power of low-frequency band in positions 1 + 2 + 3 (Power LF 1 + 2 + 3) proved to be the most selective and discriminating parameter between diabetic groups with early and severe autonomic neuropathy. CONCLUSION: The most discriminating parameters of power spectral analysis of heart rate variability for the determination of autonomic function seem to be Total Power LFHF 1 + 2 + 3 and Power LF 1 + 2 + 3.

Adult↗