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PubMedDate not supplied

Sampling frequency of the RR interval time series for spectral analysis of heart rate variability.

Spectral analysis of heart rate variability (HRV) is an accepted method for assessment of cardiac autonomic function and its relationship to numerous disorders and diseases. Various non-parametric methods for HRV estimation have been developed and extensive literature on their respective properties is available. The RR interval time series can be seen as a series of non-uniformly spaced samples. To analyse the power spectra of this series using the discrete Fourier transform (DFT), we need to interpolate the series for obtaining uniformly spaced intervals. The selection of sampling period plays a critical role in obtaining the power spectra in terms of computational efficiency and accuracy. In this paper, we shall analyse the RR interval time series from selected subjects for different sampling frequencies to compare the error introduced in selected frequency-domain measures of HRV at a constant frequency resolution for a specific duration of electrocardiogram (ECG) data. It should be pointed out that, although many other error causes are possible in the frequency-domain measures, our attention will be confined only to the performance comparison due to the different sampling frequencies. While the choice of RR interval sampling frequency (f(s)) is arbitrary, the sampling rate of RR interval series must be selected with due consideration to mean and minimum RR interval; f(s = )4 Hz was proposed for a majority of cases. This is an appropriate sampling rate for the study of autonomic regulation, since it enables us to compute reliable spectral estimates between dc and 1 Hz, which represents the frequency band within which the autonomic nervous system has significant response. Furthermore, resampled RR intervals are evenly spaced in time and are synchronized with the samples of the other physiologic signals, enabling cross-spectral estimates with these signals.

Algorithms↗
PubMed1982

Detection of occlusive disease of the carotid artery with continuous wave Doppler spectral analysis.

The accuracy of Doppler spectral analysis for diagnosing stenoses of the carotid artery was evaluated in this study. Two hundred and five patients were examined, using a 4 megahertz continuous wave Doppler velocity meter and a real-time frequency analyzer. By a comparison of the results of arteriography, peak Doppler frequencies of greater than 3.8 kilohertz were diagnostic of internal carotid artery stenoses having residual lumen diameters of 3.2 millimeters, or less, with a sensitivity rate of, 91 per cent and a specificity rate of 92 per cent. Spectral broadening, evaluated by subjective grading, yielded similar results.

Arterial Occlusive Diseases↗
PubMed1995

Pitfalls in the interpretation of spectral analysis of the heart rate variability during exercise in humans.

The recent use of spectral analysis of the R-R interval variability to assess the autonomic drive during exercise has produced inconsistent results. The purpose of this study was to assess whether the spectral components of the R-R interval variability reflect different mechanisms at rest and during exercise. Autoregressive spectral analysis of the electrocardiographic and breathing signals was performed in 11 healthy young men at rest and during incremental cycle ergometry. The amplitude of respiratory sinus arrhythmia, i.e. the absolute power of the high frequency spectral component, fell at the onset of exercise, consistent with a reduction in cardiac vagal activity. Conversely, the normalized power of the high frequency component, (i.e. the percentage of R-R interval variance due to the respiratory sinus arrhythmia) increased with increasing work rates. The low frequency spectral component of the R-R interval variability, which when expressed in normalized units is believed to reflect cardiac sympathetic activity, was no longer detectable in severe exercise when the adrenergic drive is known to be elevated. In conclusion, autoregressive spectral analysis of the R-R interval variability does not adequately reflect the autonomic changes that occur during incremental exercise. In particular, the evidence indicates that as the cardiac vagal tone falls with increasing levels of exercise, a greater percentage of the residual power of the high frequency component may be due to non-neural mechanisms.

Adult↗
PubMed1995

Alterations of sympathovagal balance in patients with hypertrophic and dilated cardiomyopathies assessed by spectral analysis of RR interval variability.

Spectral analysis of RR interval variability was performed in 35 ambulatory patients with early hypertrophic cardiomyopathy (HCMa, NYHA class I), 21 hospitalized patients with advanced hypertrophic cardiomyopathy (HCMh, NYHA class II or III), and 18 hospitalized patients with dilated cardiomyopathy (DCMh, NYHA class I, II or III). Twenty-nine ambulatory subjects (COTa) and 20 hospitalized volunteers (COTh) served as normal controls. The RR interval standard deviation (SD), the high-frequency power (HF: 0.15-0.40 Hz) corrected by the mean RR interval (CCVHF) and the normalized unit of the HF power (NUHF) served as markers of vagal modulation. Low-frequency power (LF: 0.04-0.15 Hz) corrected by the mean RR interval (CCVLF) and the normalized unit of LF power (NULF) were markers of sympathetic modulation. The LF/HF ratio was an index of sympathovagal balance. There was no significant difference in the SD, CCVHF, NUHF, CCVLF, NULF or the LF/HF ratio between the HCMa and COTa groups. At night, the SD was lower in the HCMh group relative to the COTh group (P < 0.01). The HCMh group demonstrated lower CCVHF and NUHF values (P < 0.01), higher NULF values (P < 0.01) and higher LF/HF ratios (P < 0.05) at night relative to the COTh group. Two patients who later died suddenly in the HCMh group had markedly reduced CCVHF values (0.2-0.8%) relative to the survivors in the group (mean +/- SD in the morning, afternoon and night, 1.07 +/- 0.43%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1997

Autonomic nervous system activity during tilt testing in syncopal patients, estimated by power spectral analysis of heart rate variability.

Spectral analysis of heart rate variability (HRV) was used to assess changes in autonomic function before and during postural tilt in 28 syncopal patients: 14 (group A) with positive and 14 (group B) with negative tilting test, and 14 normal controls (group C). Frequency-domain measurements of the high (HF) and low (LF) frequency bands and the ratio LF/HF were derived from Holter recordings, computed by Fast Fourier analysis for 4-minute intervals immediately before tilt testing, immediately after tilting, and just before the end of the test. In group A, the mean values of LF and HF decreased slightly in response to tilting while the LF/HF ratio increased, though these changes were not statistically significant. All parameters showed a statistically significant increase just before the onset of syncope. In group B, there were no significant changes in the parameters measured throughout the test. In group C, there was an increase in the LF and LF/HF ratio and a decrease in the HF immediately after tilting. There were no further significant changes in any of the parameters during the test. Syncopal patients have a different pattern of response to the orthostatic stimulus, in that they do not show the increase in sympathetic tone observed in normal individuals immediately after tilting. In the patients with a positive tilt test, there is a shift in the balance of ANS activity towards the sympathetic system shortly before the onset of syncope.

Autonomic Nervous System↗
PubMed1997

[Autonomic nervous function in patients with vertigo--evaluation for static function, variation and dynamic change using power spectral analysis of RR intervals].

Power spectral analysis of RR intervals (PSA) of 94 vertiginous patients with associated autonomic nervous dysfunction (AND group), 31 patients with vertebro-basilar insufficiency (VBI group) and 25 controls were analyzed in supine and upright positions. In addition static function, variation from the supine to the upright position and dynamic change in autonomic nervous function (ANF) from the supine to the upright position were examined. Heart rate was recorded for 120 seconds in the supine and 40 seconds in the upright position. RR intervals for each 20-second period were computed using FFT (Fast Fourier Transformation), and the ratio of low frequency power (0.05-0.15 Hz) to high frequency power (0.15-0.4 Hz) (L/H) of PSA were analyzed as an index of sympathetic activity. The PSA was examined by the following three parameters; L/H at rest during the 80-second period from 20 to 100 seconds (static function), the L/H variation between each 20-second period from 0 to 160 seconds (variation) and the ratio of L/H to that in the upright position (dynamic change). The results of PSA were compared with those of pulse wave velocity (PWV) and the coefficient of variation of the RR interval (CVRR), and association between attacks of vertigo and ANF was determined. The results of static function of PSA and the results of PWV and CVRR were very similar, indicating that both methods are useful for evaluating ANF in vertiginous patients. In the AND group the variation in sympathetic activity tended to be larger in patients with sympathetic hyperfunction and parasympathetic hypofunction and in the patients with sympathetic hypofunction and parasympathetic hyperfunction resulting from PWV and CVRR, than in the controls. The dynamic change in patients with sympathetic hyperfunction and parasympathetic hypofunction resulting from PWV and CVRR was also significantly lower than that in the controls (p < 0.01). Some patients in the AND group already showed excessive sympathetic hyperfunction at rest, and changing the position from supine to upright might trigger sympathetic hypofunction, causing an attack of vertigo. The PSA results in the VBI group were similar to those in the controls, suggesting that sympathetic dysfunction did not affect VBI induced vertigo.

Adolescent↗
PubMed2003

Spectral analysis of cerebrovascular regulation in patients with autonomic dysfunction.

BACKGROUND: Regulation of cerebral blood flow during orthostatic stress has been a major research topic in patients with orthostatic intolerance such as autonomic dysfunction. Spontaneous fluctuations of middle cerebral artery blood flow velocity (MCAFV) recorded with transcranial Doppler (TCD) have been found to contain information related to cerebrovascular regulation, which can be deciphered with spectral analysis. The purpose of this study was to evaluate the differences in cerebrovascular regulation between healthy volunteers and patients with autonomic dysfunction and orthostatic dizziness for using spectral analysis of MCAFV information derived from TCD during supine rest and orthostasis. METHODS: Thirteen patients with autonomic dysfunction and orthostatic dizziness were found to have impaired cerebral autoregulation because of failure to maintain adequate cerebral blood flow velocity during a 30-minute head-up tilt study with concomitant TCD and cuff sphygomanometer monitoring. The data of bilateral MCAFV were compared between these 13 patients and 9 healthy volunteers using spectral analysis. RESULTS: Spectral analysis of the MCAFV showed significantly decreased low frequency (LF) power in supine position in the patient group (p = 0.0002). In addition, the spectral power in the very low and low frequency (VLF & LF) ranges remained significantly lower in the patient group after tilting up (p < 0.05). CONCLUSIONS: (1). Our study results further support the previous findings that the LF component of the spontaneous fluctuations of MCAFV is important for cerebrovascular regulation. (2) The decreased LF MCAFV power may be a useful indicator or marker of impaired cerebrovascular regulation in patients with autonomic dysfunction.

Aged↗
PubMedDate not supplied

[Spectral analysis of the variations in heart rate and cardiac activation on waking up in sleepwalking].

INTRODUCTION: In sleepwalking, a disorder that is characterised by partial waking, the subject experiences an alteration of the microstructure of sleep that can affect autonomous activity during sleep and the waking state. AIMS: In order to evaluate any possible upset in the regulation of autonomous functioning in sleepwalkers during sleep and the waking state, we conducted a spectral analysis of their heart rate variability (HRV) during both sleep and the waking state. SUBJECTS AND METHODS: Spectral analysis of HRV was conducted in the group of 10 sleepwalkers and 10 normal controls during sleep and during the waking state in both the horizontal and vertical positions. Their pattern of cardiac activation was also analysed during different types of arousal. RESULTS: There were no differences between the group of sleepwalkers and the control group in the parameters used in the spectral analysis of HRV during sleep and in the horizontal position during the waking state. Sleepwalkers showed a greater shift in the sympathovagal balance in favour of sympathetic activity, as a response to standing. During the 5-minute sequences immediately before the start of pathological arousal in sleepwalkers, the total energy in the spectral analysis of HRV was seen to increase. No differences were found between the patterns of cardiac activation displayed by the groups of patients and normal subjects during several different types of arousal. CONCLUSIONS: Autonomous reactivity was seen to be altered as a response to the orthostatic load in sleepwalkers, which could be the consequence of the instability of these patients' sleep. The increase in the total energy in the spectral analysis of HRV immediately before pathological arousal during NREM 4 sleep in sleepwalkers suggests that autonomous activation precedes cortical arousal.

Adolescent↗
PubMedDate not supplied

[Evaluation of injuries features inflicted by shots from gas guns by emission spectral analysis].

The authors describe a methodological approach to emission spectral analysis of material evidences aimed at evaluating the regularities of deposition of the shot metals at the site of injuries inflicted by gas guns. Injuries inflicted by gunshots with chemical cartridges and with shot cartridges, with and without obstructions, from different distances have been examined. The detected regularities may be useful in forensic medical expert evaluations by means of emission spectral analysis in cases with gas gunshots.

Air↗
PubMedDate not supplied

Effectiveness of high resolution ECG spectral analysis in discrimination of patients prone to ventricular tachycardia and fibrillation.

INTRODUCTION: To improve the diagnostic power of high resolution electrocardiography for discriminating patients at risk of ventricular arrhythmias, new methods based on spectral analysis have been used in recent years. The purpose of this study was to evaluate the effectiveness of these methods for predicting the risk of ventricular tachycardia and ventricular fibrillation in patients after myocardial infarction. MATERIAL AND METHODS: High resolution ECG were recorded in 129 post-infarction patients and 23 healthy volunteers. Of the post-infarction patients: 62 presented with ventricular tachycardia, 23 with ventricular fibrillation, while 44 had no clinically relevant arrhythmias. The ECG signals were recorded in three orthogonal X, Y, Z leads and averaged using cross-correlation method. Spectral analysis was performed by fast Fourier transform and the parametric modeling method with autoregressive model. Spectral analysis data were evaluated quantitatively by computing normality factor for FFT and spectral factor for AR. RESULTS: Both methods were found to be useful for evaluating the risk of arrhythmias. The sensitivity of ventricular tachycardia risk evaluation was higher (81%--FFT, 73%--AR) than that of evaluating the risk of ventricular fibrillation (30%--FFT, 48%--AR). The specificity in post-infarction patients without arrhythmias (93%--FFT, 84%--AR) was as high as that in healthy subjects (96%--FFT, 87%--AR). CONCLUSIONS: Spectral analysis of HRECG is an effective method for evaluating the risk of VT and VF in patients after myocardial infarction.

Adult↗
PubMed1998

Pharmacokinetic assessment of novel anti-cancer drugs using spectral analysis and positron emission tomography: a feasibility study.

PURPOSE: The aim of this study was to investigate the feasibility of evaluating the pharmacokinetics of radiolabeled anti-cancer drugs using spectral analysis, a non-compartmental tracer kinetic modeling technique, and positron emission tomography (PET). METHODS: Dynamic PET studies were performed on patients receiving tracer doses of 5-fluorouracil (5-[18F]-FU) and two developmental drugs [11C]-temozolomide and [11C]-acridine carboxamide. Spectral analysis was then used to (a) determine individual and group average pharmacokinetics, (b) predict tumour handling in response to different drug administration regimens, and (c) produce functional parametric images describing regional pharmacokinetics. RESULTS: Spectral analysis could distinguish tumour kinetics from normal tissue kinetics in an individual [11C]-temozolomide study and demonstrated a markedly greater volume of distribution (VD) in glioma than in normal brain, although there was no appreciable difference in mean residence time. Analysis of pooled acridine carboxamide data (n = 22) revealed a relatively large VD (and prolonged retention) in the liver and spleen and a markedly lower VD (and initial uptake) in the brain. Continuous infusion of 5-[18F]-FU was predicted to achieve a concentration in colorectal metastases in liver approximately 10 times that achieved in plasma at 10 h after commencement of the infusion. CONCLUSIONS: We conclude that spectral analysis provides important pharmacokinetic information about radiolabeled anti-cancer drugs with relatively few model assumptions.

Acridines↗
PubMed1999

Oximetry spectral analysis in the diagnosis of obstructive sleep apnoea.

Using spectral analysis of oximetry data, we prospectively evaluated the validity of this methodology in patients clinically suspected of suffering from obstructive sleep apnoea (OSA). A total of 233 outpatients were studied. Nocturnal oximetry was performed simultaneously with conventional polysomnography for all participants. The power density of oxygen saturation was analysed using Fast-Fourier transformation of the oximetric signal. Nocturnal oximetry test results were considered as abnormal (suspicion of OSA) if a peak in the spectrum between the period boundaries 30 and 70 s was observed. A normal test result was defined as the absence of the 30-70 s peak from the spectrum. Single-blind evaluation was performed by three independent observers, and agreement of two or more of these was considered definitive. The peak amplitude and the ratio of the area enclosed in the 30-70 s peak to the total area of the spectrum (r(S)) were measured. The presence of a peak has a sensitivity of 78%, a specificity of 89%, a positive predictive value of 89% and a negative predictive value of 78%. Apnoea-hypopnoea indexes were correlated significantly with peak amplitude (r=0.74; P<0.001) and with r(S) (r=0.69; P<0.001). For a peak amplitude threshold of 0.7%(2), the sensitivity was 94% and the specificity was 65% for OSA diagnosis. Using a threshold for r(S) of 0.15, the sensitivity was 91% and the specificity was 67%. Thus the spectral analysis of nocturnal oximetry and identification of a peak at 30-70 s could be useful as a diagnostic technique for OSA subjects.

Adult↗
PubMed1996

Spectral analysis of clinical signals: an interface between medical statisticians and medical engineers.

This paper reviews the current use of spectral analysis in clinical medicine. We cover the problems of aliasing and estimation of the spectrum using windowing and autoregressive techniques. These techniques are modified for nonstationary data to include evolutionary spectral analysis and recursive autoregressive methods. The relationship between evolutionary spectral analysis and the time-frequency methods such as the Wigner-Ville distribution is discussed. Other techniques covered are Walsh Transforms and cosinor analysis. The methods are shown to apply in the analysis of signals from heart rate, blood pressure, EEG, other electrical signals and hormone levels. The engineering and statistical approaches are contrasted.

Blood Pressure↗
PubMed2001

Comparison between the Fourier and Wavelet methods of spectral analysis applied to stationary and nonstationary heart period data.

The aim of this study was to assess the error made by violating the assumption of stationarity when using Fourier analysis for spectral decomposition of heart period power. A comparison was made between using Fourier and Wavelet analysis (the latter being a relatively new method without the assumption of stationarity). Both methods were compared separately for stationary and nonstationary segments. An ambulatory device was used to measure the heart period data of 40 young and healthy participants during a psychological stress task and during periods of rest. Surprisingly small differences (<1%) were found between the results of both methods, with differences being slightly larger for the nonstationary segments. It is concluded that both methods perform almost identically for computation of heart period power values. Thus, the Wavelet method is only superior for analyzing heart period data when additional analyses in the time-frequency domain are required.

Adolescent↗
PubMed1981

Spectral analysis vs. period-amplitude analysis of narrowband EEG activity: a comparison based on the sleep delta-frequency band.

This paper presents a comparison of spectral analysis with period-amplitude analysis when applied to the quantification of narrowband electroencephalographic (EEG) activity. In particular, it examines their respective usefulness in quantifying on the average the electrographic content within the delta-frequency band of EEG epochs during human stage 4 sleep. It is shown that while the power spectrum efficiently quantifies the overall power trends in the EEG data, period-amplitude analysis seems to offer more resolution than the power spectrum in detecting electrographic details in amplitude and incidence within relatively narrow frequency bands. Examples are given of the sensitivity of spectral analysis ot both wave amplitude and incidence, and of the fact that--due to the inherent averaging process in the power spectrum generation--spectral analysis cannot differentiate between low-amplitude, high-incidence EEG activity and high-amplitude, low-incidence EEG activity, in contradistinction to period-amplitude analysis. It is also shown that although two EEG epochs may exhibit similar power spectrum plots, their corresponding period-amplitude plots may not be similar. It is emphasized that discrepancies may exist when comparing spectral to period-amplitude analysis due to differences in the definition of "frequency" in the two techniques.

Adult↗
PubMed2003

[Assessment of the changes in autonomic nervous function during head up tilt test in syncopal patients using spectral analysis of heart rate variability].

OBJECTIVE: To study the pathological mechanism of vasovagal syncope, spectral analysis of heart rate variability was used to evaluate the changes of autonomic function during head up tilt test in patients with unexplained syncope. METHODS: 27 patients with recurrent episodes of unexplained syncope underwent 70 degrees head up tilt test. Spectral analysis was used to assess the changes in autonomic function before tilt testing, immediately after tilting, just before the occurrence of syncope or at the end of the test, during the syncope period or at the end of the test and after testing in supine rest. At the same time, haemodynamic changes were recorded. Spectral power in very low frequency (VLF, 0.003 - 0.04 Hz), low frequency (LF, 0.04 - 0.15 Hz) and high frequency (HF, 0.15 - 2.00 Hz) were computed with Fast Fourier Transform analysis, and LF and HF were normalized: LF norm = 100 x LF/(TP-VLF) and HF norm = 100 x HF/(TP-VLF). RESULTS: 12 patients (mean age 40 +/- 10 years) showed a negative response and 15 patients (mean age 37 +/- 9 years) showed a positive response. Both systolic and diastolic blood pressure decreased in all the patients [(118.00 +/- 10.42-->81.00 +/- 12.36) mm Hg, P < 0.01 and (76.00 +/- 8.40-->52.00 +/- 10.95) mm Hg, P < 0.01] and heart rate decreased in 8 patients (53%). No significant difference in all the indices of spectral analysis was observed in supine position between the subjects with positive and negative test results. LF norm in both the groups did not alter during the entire tilt procedure. The decreased HF norm and increased LF/HF persisted throughout head up tilt test in the negative patients. In the positive patients, similar patterns of changes were observed before the occurrence of positive symptoms, and during the occurrence of the symptoms. HF norm abruptly rose (10.47 +/- 4.04-->32.95 +/- 10.48) and obviously exceeded that before tilt testing (23.44 +/- 4.20-->32.95 +/- 10.48, P < 0.05) and LF/HF dropped (3.28 +/- 0.39-->1.07 +/- 0.31, P < 0.01). At supine rest just after test, all the indices in both groups came back. CONCLUSIONS: In the supine position, autonomic function is similar between positive and negative subjects. Positive patients have a different pattern of response to the tilting test. The pathological mechanism leading to vasovagal syncope appears to be related with the abrupt and excessive increase of vagal activity.

Adult↗
PubMed2000

[Spectral analysis of fetal heart rate variability].

OBJECTIVE: To assess power spectral densities and power spectrum of FHR variability in two categories of fetal activity, quiescence and breathing movements, in pregnancies complicated by diabetes mellitus or intrauterine growth retardation. MATERIAL AND METHODS: The study group included 70 women, 35 in uncomplicated pregnancies and 35 with above-mentioned complications. The spectral analysis of FHR variability in fetal quiescence or breathing activity was performed. The power spectrum was analyzed at frequencies 0-1.0 Hz. Successively, the power spectral density was calculated. It has been presented the plots of spectral densities of beat-to-beat variabilities well during breathing episodes as "no breathing". Subsequently, the power spectra were calculated in both analyzed activities and groups. RESULTS: The highest values of power spectral densities (0.118 +/- 0.025) at 0.6-0.8 Hz were found in uncomplicated pregnancies. In pregnancies complicated by diabetes mellitus (0.048 +/- 0.049) or IUGR (0.042 +/- 0.041) these values were statistically significantly. At 0.6 Hz and 0.8 Hz power spectra of FHR variability were lower in quiescence comparing to breathing activity, as well in uncomplicated as complicated pregnancies. At these frequencies power spectra during breathing movements were significantly lower in complicated pregnancies comparing to uncomplicated. COMMENTS: The results of this study confirm the usefulness of spectral analysis in the assessment of FHR variability. The observed disturbances may reflect an abnormal fetal reactivity. The evaluation of breathing and cardiovascular systems interaction allows to study indirectly the central nervous system that coordinates both activities.

Blood Flow Velocity↗
PubMed1995

EEG spectral analysis in vascular and Alzheimer dementia.

The role of EEG spectral analysis in the diagnosis of syndromes of dementia is still disputed. Since there have been few studies dealing with the profile of power spectra, the present investigation has focused on this aspect, constructing power spectra taken from 16 derivations and calculated by averaging twenty 2 sec epochs, using a serial array of frequencies from 1 to 32 Hz. The spectral analysis of the EEG, recorded under awake resting eyes closed (REC) and open (REO) conditions, was performed in 50 patients with Alzheimer's disease (AD), 37 with vascular dementia (VaD) and 36 elderly controls. Three spectral profiles were found under REC: (i) type A, showing a dominant 6.5-12 Hz peak (44% AD, 97.3% VaD), although lower than in controls; (ii) type B, lacking a dominant peak in the 6.5-12 Hz band, but characterised by high power in 1-6.5 Hz band (44% AD, 2.7% VaD); (iii) type C, corresponding to a flat, low voltage, spectrum (12% AD). Unlike controls, demented patients showed an increased REO/REC power ratio in the 6.5-12 Hz band, especially in those with type B spectra. AD patients with type B spectra had an earlier age of disease onset.

Aged↗