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PubMed1996

Spectral analysis of muscle fiber images as a means of assessing sarcomere heterogeneity.

A new image-analysis-based method is described for assessing sarcomere heterogeneity in skinned rabbit psoas muscle fiber segments. This method consists of off-line, two-dimensional Fourier spectral analysis of video-taped muscle images. Local sarcomere length is assessed by partitioning the muscle images into half and quarter images spanning the original image and analyzing the associated spectra. The spectra are analyzed in two different ways, yielding two measures of sarcomere length. The first measure is obtained by calculating and inverting the centroid frequency of the first-order peak associated with each two-dimensional Fourier spectrum. The second measure is obtained in a similar manner, the only difference being that the two-dimensional spectra are first collapsed into one-dimensional line spectra by summing the pixels perpendicular to the fiber axis. Comparison of the two measures provides a measure of striation skewness that cannot be obtained by other image analysis based methods that determine sarcomere length by analyzing selected line luminance profiles.

Animals↗
PubMed1994

[The spectral analysis of heart rate variability. The methodological aspects].

OBJECTIVES: A study is made of the influence of methodology on the analysis of cardiac cycle variability in terms of frequency and time domains. METHODS: Twenty-five individuals were divided into three groups: 1) non-smokers (n = 10); 2) smokers (n = 8); and 3) non-smokers without guided respiratory frequency (n = 7). An analysis was made of RR variability during 5 min intervals in time domain (standard deviation, variation coefficient, and difference between maximum and minimum RR), and frequency domain (spectral analysis, Fast Fourier Transform algorithm using 5 types of data windows). RESULTS: On comparing the results obtained in the 25 individuals with the 5 data windows, significant differences were observed (ANOVA; p < 0.001) in maximum and total amplitudes of the spectrum (in absolute terms) in the low frequency band (0.04-0.15 Hz). No significant differences were found between the normalized values or between the low/high (0.15-0.40 Hz) frequency ratio: W1 = 1.63 +/- 0.30; W2 = 1.62 +/- 0.29; W3 = 1.65 +/- 0.31; W4 = 1.52 +/- 0.26, and W5 = 1.55 +/- 0.27 (X +/- SE). On averaging the RR intervals each 5 cycles, significant differences were encountered for great part of the parameters studied. No significant differences were encountered for great part of the parameters studied. No significant differences were noted between the non-smokers as regards the use or non-use of a metronome (low/high frequency ratio in group 1 = 1.85 +/- 0.39 vs group 3 = 1.78 +/- 0.43; NS). The linear regressions between the variability parameters in terms of time and frequency domains (absolute values), and age (group 1) were significant, with greater regression coefficients on using the linear transformation of an exponential model. On comparing groups 1 and 2, a non statistically significant trend towards smaller maximum and total amplitudes (absolute values) was noted in group 2 for both frequency bands. CONCLUSIONS: 1) The type of data window (Fourier analysis) introduces significant modifications of some parameters expressed in absolute values, but not between normalized values; 2) signal averaging greatly modifies the information obtained; 3) the decrease in variability parameters observed with age fits better to an exponential model; 4) no differences were detected on guiding or not respiratory frequency, and 5) smoking appears to induce a tendency towards reducing cardiac cycle variability.

Adult↗
PubMed1996

Autoregressive spectral analysis of phrenic neurogram during eupnea and gasping.

During hypoxic gasping, the phrenic neurogram (PN) has a steeper rate of rise, an augmented amplitude, and a shorter duration than is seen during eupnea. Because hypoxia reduces neuronal activity, we hypothesized that gasping would be characterized in the frequency domain by enhanced low-frequency power compared with eupnea. Autoregressive (AR) spectral analysis of the PN in chloralose-anesthetized, vagotomized, peripherally chemodenervated cats was performed during eupnea and hypoxic gasping. During eupnea, significant spectral peaks were seen at 41 +/- 2 and 93 +/- 2 (SE) Hz. In all cats, the 41-Hz spectral peak disappeared during hypoxic gasping and was replaced by a high-power, low-frequency peak at 26 +/- 1 Hz. No consistent change in the frequency or power of the high-frequency spectral peak was seen during gasping. To determine whether changes in the AR spectrum of the PN during gasping result from augmented respiratory output, we compared the AR spectra of the PN during gasping, hypercapnia (end-tidal CO2 fraction = 0.09), and carotid sinus nerve stimulation. Unlike during gasping, there was no shift in power toward lower frequencies during hypercapnia and carotid sinus nerve stimulation. We conclude that the spectral characteristics of gasping, loss of the medium-frequency peak and the appearance of low-frequency (< 30-Hz) power, are unique to this respiratory pattern.

Animals↗
PubMed1987

The choice of the wavelengths in spectral analysis: an application to determine the composition of a tetraribonucleotide mixture.

We present a simple program running on a pocket computer allowing us to determine the order of importance of the wavelengths (regarding the accuracy of the results) in spectral analysis and to evaluate the absolute errors made on the determination of the concentrations of the constituents. We have applied this programme to the determination of the composition of a tetraribonucleotide mixture and have compared our results with other results published.

Microcomputers↗
PubMed1991

Sympathovagal interaction during mental stress. A study using spectral analysis of heart rate variability in healthy control subjects and patients with a prior myocardial infarction.

We tested the hypothesis that psychological stress testing in the clinical laboratory provokes changes in the sympathetic and vagal activities regulating heart rate that can be assessed noninvasively using spectral analysis of RR variability. To account for the effects on respiration produced by talking, this study was performed with two different procedures: the I.K.T. (i.e., a computer-controlled mental task that is performed in silence and does not entail human confrontation) and a stressful interview. Finally, we assessed whether ischemic heart disease modifies the spectral changes induced by psychological stress by comparing a group of healthy subjects (age, 38 +/- 2 years) with a group of patients (age, 52 +/- 3 years) recovering from 1-month-old myocardial infarctions. The findings indicate that psychological stress induced marked changes in the sympathovagal balance, which moved toward sympathetic predominance. The low-frequency component of RR variability, a marker of sympathetic activity, increased from 58 +/- 5 normalized units (NU) to 68 +/- 3 NU with the I.K.T. and to 76 +/- 3 NU with the interview. This increase was absent in the group of post-myocardial infarction patients. However, arterial pressure increased significantly in both groups of subjects. The possibility of age playing an important role in determining the differences observed was disproved by the findings of a marked increase in low frequency with mental stimuli in an additional group of borderline hypertensive subjects with ages (55 +/- 2 years) comparable to those of post-myocardial infarction patients.

Adult↗
PubMed2001

[Spectral analysis of muscle sympathetic nerve activity in man].

Recent applications of frequency domain analysis to the variability of muscle sympathetic nerve activity (MSNA) have improved the comprehension of the relationship between cardiovascular oscillations and the autonomic nervous system. It has been observed that spectral analysis of MSNA is characterized by two major oscillatory components at low (LF) and high (HF) frequencies, similar to those detectable in the variability of cardiovascular signals. Pharmacological and non-pharmacological studies have shown that, at least within the physiological range, the two MSNA rhythms show a reciprocal behavior, similar to that already observed for cardiovascular oscillations. The oscillatory pattern of MSNA provides non-redundant but complementary information with respect to the time domain measures of MSNA (burst rate and amplitude) since it has been shown that completely different spectral profiles may be derived from various MSNA recordings. On the other hand, the latter are instead comparable in terms of mass activity. Due to the intrinsic characteristics of the signal, which represents the direct outflow of the central neural structures of the cardiovascular autonomic nervous system, this approach can be considered as a unique window over the central organization of excitatory and inhibitory neural mechanisms responsible for the genesis and the regulation of cardiovascular oscillations.

Electrophysiology↗
PubMed2002

Postprandial hypotension in elderly subjects: spectral analysis of heart rate variability and electrogastrograms.

BACKGROUND: In order to clarify the mechanism of postprandial hypotension in the elderly, the influence of gastric motility and autonomic nervous activity on hypotensive reactions after meals was investigated, using electrogastrograms (EGGs) and spectral analysis of heart rate variability. METHODS: EGGs, heart rate variability, blood pressure, and blood catecholamine levels before and after a meal were measured in 20 healthy young subjects (mean age, 25.6+/-5.6 years; young group) and in 20 healthy elderly subjects (mean age, 78.3+/-5.6 years; elderly group). RESULTS: In the analysis of heart rate variability, no significant changes were observed in the low-frequency component (LF power), high-frequency component (HF power), or LF/HF ratio after the meal in the young group. In the other hand, the LF/HF ratio was significantly increased after the meal in the elderly group. In the EGG analysis, the peak power amplitudes after the meal were significantly increased compared with those before the meal in both groups. After the meal, the peak power amplitudes in the young group were significantly greater than those in the elderly group. The baseline blood noradrenaline level (before the meal) was higher in the elderly group than in the younger group, but the level of this catecholamine in the elderly group did not increase significantly after the meal. CONCLUSIONS: It is suggested that the down-regulation of catecholamine may be one of the causes of postprandial hypotension in the elderly. The response to secreted catecholamine and the compensatory response to decreased blood flow in the systemic circulation were impaired in the elderly group, which finding may explain the high incidence of postprandial hypotension in the elderly subjects.

Adult↗
PubMedDate not supplied

All night spectral analysis of EEG sleep in young adult and middle-aged male subjects.

The sleep EEGs of 9 young adult males (age 20-28 years) and 8 middle-aged males (42-56 years) were analyzed by visual scoring and spectral analysis. In the middle-aged subjects power density in the delta, theta and sigma frequencies were attenuated as compared to the young subjects. In both age groups power density in the delta and theta frequencies declined from NREM period 1 to 3. In the sigma frequencies, however, no systematic changes in power density were observed over the sleep episode. In both age groups the decay of EEG power (0.75-7.0 Hz) over successive NREM-REM cycles and the time course of EEG power during NREM sleep was analyzed. The decay rate of both EEG power density over successive NREM-REM cycles and EEG power density during NREM sleep was smaller in the middle-aged subjects than in the young subjects. It is concluded that the age-related differences in human sleep EEG power spectra are not identical to the changes in EEG power spectra observed in the course of the sleep episode. Therefore age-related differences in EEG power spectra cannot be completely explained by assuming a reduced need for sleep in older subjects. The smaller decay rate of EEG power during NREM sleep in the middle-aged subjects is interpreted as a reduced sleep efficiency. The results are discussed in the frame work of the two-process model of sleep regulation.

Adult↗
PubMed2000

Sleep-EEG modulation of interictal epileptiform discharges in adult partial epilepsy: a spectral analysis study.

INTRODUCTION: In order to define accurately the relationship between EEG components (spindles, delta and theta frequencies) and the occurrence of interictal epileptiform discharges (IED) during sleep in partial epilepsy, a correlation study between spike overnight distribution and EEG spectral power time series was performed. METHODS: Eighteen patients (mean age: 24.7+/-5.5 years) affected by partial epilepsy underwent continuous EEG-polysomnography. The temporal series of Slow Wave Activity (SWA), Sigma Activity (SA) and Theta Band (TB), derived from spectral analysis, were obtained from a spike-free and pathologic alteration-free derivation, contralateral to the most active lead, where the IED count was performed. Relationships between SA, SWA and TB and time series of IED were tested by means of correlation techniques after data normalization. RESULTS: Our results revealed a significantly higher correlation between IED and SWA in 12 subjects; a significantly higher correlation between IED and SA in three subjects and a significant correlation with TB in three cases. CONCLUSIONS: Data suggest that in most adult patients with partial epilepsy IED production during sleep is facilitated by the action of synchronizing mechanisms which are active during NREM sleep and lead to the appearance of EEG delta waves. Nevertheless evidence is given of two smaller groups of patients. In one of them IED are more sensitive to the promoting action of the spindle generating mechanism, active during stage 2 of NREM sleep. In the other one the promoting action of TB, characterizing EEG during stage 1 and REM sleep, is evident.

Adult↗
PubMed2001

Radiofrequency spectral analysis of attenuated ultrasound signals in experiments with echo contrast microbubbles.

Conventional gray-scale myocardial contrast echocardiography cannot distinguish perfused but attenuated from nonperfused myocardium because both may appear similar at low image intensity. We hypothesized that with radiofrequency spectral analysis of attenuated ultrasound signals, the harmonic-to-fundamental frequency ratio of the peak power spectrum (HFR(P)) could determine the presence of contrast microbubbles. We measured frequency responses of Optison microbubbles at defined degrees of ultrasound signal attenuation with different formulations of silicone (55D, 80A, and 3M); gray-scale intensities of Optison plus water compared with degassed water were analyzed at different attenuation settings (-25, -32, and -44 dB, respectively). HFR(P) values of Optison plus water were significantly higher than reference values of degassed water at each attenuation setting (55D, -14 +/- 2 dB versus -30 +/- 2 dB, P <.001; 80A, -19 +/- 2 dB versus -30 +/- 3 dB, P <.01; 3M, -22 +/- 2 dB versus -30 +/- 3 dB, P <.05), even though conventional videodensitometric analysis could not distinguish them. HFR(P) analysis objectively detects microbubbles in clinically relevant conditions of attenuation.

Contrast Media↗
PubMed1982

Self-induction of epileptic seizures by eye-closure. Spectral analysis of concomitant EEG.

The spectral characteristics of the EEG were studied in the period immediately preceding slow eye-closures associated with the self-induction of epileptiform activity. Power levels were compared with similar spontaneous eye-closures not associated with paroxysmal activity, with eye closures performed to command, and with EEG preceding eye-blinks. A transient rise in EEG power at low frequencies 1-2 seconds before the slow eye-closure was found to be reliably associated with the subsequent occurrence of paroxysmal activity. This finding suggests that eye-closure may not be initial event in the sequence culminating in paroxysmal activity.

Adolescent↗
PubMed1991

Changes in sympathetic and parasympathetic cardiac activation during mental load: an assessment by spectral analysis of heart rate variability.

Spectral analyses of heart rate (HR) and blood pressure (BP) fluctuations yield three typical peaks at a low (0.02-0.06 Hz), a mid (0.07-0.14 Hz) and a high (around the respiratory frequency) frequency area. These so-called bands attract the interest of researchers because they seem to offer the facility of non-invasively studying autonomic cardiovascular control mechanisms. The high frequency component is solely under vagal control, the influence of sympathetic/vagal efferents on the low and mid frequency band is unclear. We therefore investigated in a single case study (23 year old male) the effects of propanol (0.06 mg/kg, 30 min. interruption, 0.12 mg/kg i.v.), dobutamine (1.14 micrograms/kg/min for 30 minutes, then 2.21 micrograms/kg/min i.v., then 4.42 micrograms/kg/min), atropine (0.01 mg/kg within 5 minutes, 30 minutes later 0.02 mg/kg within 5 minutes), and carbachol (0.125 mg, 30 min. interruption, 0.25 mg s.c.) upon HR, HR-variability spectra, BP and respiratory parameters at rest and during 5 minutes of a mental task. Under all four drug conditions BP is elevated at rest and mental stress, the latter always giving higher results than the former. Atropine shortens interbeat intervals (IBI) by almost 50 percent (from 939 msec to 514 msec), the high dose of dobutamine reduces IBI from 725 to 580 msec, propranolol increases interval length by 10 percent. Drug effects on spectral bands give clear results with atropine: It reduces spectral energy in all three frequency bands at rest and during mental stress. The other drugs show no clear-cut effects on HR-variability spectra. Even though results of a single case study should be interpreted with great caution we believe that the following conclusion can be made: At rest and during short-lasting mental stress all frequency bands in HR-variability spectra are to a large extent under parasympathetic control.

Adult↗
PubMed2004

Short-term spectral analysis of heart rate variability during supine-standing-supine test in patients with paroxysmal atrial fibrillation.

The aim of the study was to assess the sympathovagal balance in group of 27 patients without significant structural heart disease after an attack of atrial fibrillation. The investigation was performed using spectral analysis of heart rate variability during examination under conditions of different orthostatic loads in single phases, called the supine-standing- supine test. The findings were compared with a group of healthy persons. These revealed a significantly decreased total spectral power (430.7 vs 1558.0 ms(2) supine1; 477.6 vs 1042,5 ms(2) standing; 567.5 vs 1948.5 ms(2) supine2), and spectral power of the high frequency spectral component (140.8 vs 619.3 ms(2) supine1; 96.2 vs 203.3 ms(2) standing; 186.3 vs 739.4 ms(2) supine2) in the studied group of patients in comparison with the control group.

Adult↗
PubMed1984

Spectral analysis of the surface electromyogram as a tool for studying rate modulation: a comparison between theory, simulation, and experiment.

Theoretical work suggests that if the interpulse intervals ( IPIs ) of motor unit action potential trains ( MUAPTs ) are independently and normally distributed, then spectral analysis of the electromyogram could be a useful tool for studying rate modulation by virtue of the presence of a peak in the power spectrum at the average firing frequency of all active motor units. It is shown in this paper that IPIs need not be normally distributed, specifically that the results are very much the same if the IPIs are distributed according to a Gamma probability density function ( PDF ). Simulation of the electromyogram based on this theory proved the applicability of the method. Experimental results obtained for the masseter, biceps brachii and first dorsal interosseus (FDI) muscles, however, were in disagreement with both theory and simulation except for the biceps muscle at force levels up to 20% of the maximal force and for the masseter and FDI muscles in 1 out of 5 subjects. This indicates that the models for MUAPTs hitherto used might not be generally correct. Apart from this discrepancy, our results reveal differences between masseter and FDI muscles on the one hand and the biceps brachii on the other, which indicate that motor unit synchronisation is much more pronounced in the latter muscle.

Action Potentials↗
PubMed1984

Spectral analysis of fetal heart rate in sheep: the occurrence of respiratory sinus arrhythmia.

Respiratory sinus arrhythmia is a pattern of rhythmic variation in the heart rate that occurs at the frequency of respiration and is mediated principally by the vagus nerve. Spectral analysis can decompose the variance of a series of sequential measures into constituent frequencies to measure and verify whether there is respiratory sinus arrhythmia in utero in the fetal lamb. Recordings of heart period were obtained from electrodes implanted under fetal skin in six chronic preparations. Respiratory rate and heart period were recorded immediately after delivery and daily for the next 5 days. Respiratory sinus arrhythmia was clearly demonstrated in the neonatal lambs, and the same frequency of respiratory sinus arrhythmia was observed in the fetus and in the newborn lamb (0.8 to 0.1 Hz). There was a reproducible pattern of change in respiratory sinus arrhythmia from 27 days before delivery until term, with a decline in the amplitude of respiratory sinus arrhythmia 4 to 8 days before delivery. We conclude that respiratory sinus arrhythmia was demonstrated in fetal sheep and may serve as an indicator of the integrity of the central nervous system in the fetus and the neonate.

Animals↗
PubMed1987

Hemodynamic regulation in SHR: investigation by spectral analysis.

This work is based on the premise that hypertension in the spontaneously hypertensive rat (SHR) is a consequence of an imbalance in autonomic cardiovascular control. Spontaneous, instantaneous fluctuations in heart rate (HR) and arterial blood pressure (ABP) were studied by spectral analysis in age-matched groups of SHR and normotensive Wistar-Kyoto (WKY) rats. Continuous recordings of ABP and HR made in conscious, unrestrained, young 1-, 2-, 3-, and 6-mo-old rats show that power spectra of HR fluctuations were similar in both strains, whereas ABP fluctuations were significantly different in the low, presumably vasomotor frequency range being reduced in SHR as compared with age-matched WKY rats. In 1-mo-old rats, the difference between strains became smaller with urethan anesthesia and disappeared with spinalization, suggesting that it might have originated in some disparity between the strains at the level of the central nervous system. Low doses of phentolamine elicited a fall in low-frequency ABP fluctuations of WKY but a rise in SHR, whereas larger doses produced a fall in the power of both. In SHR, reduction in the power spectrum of ABP fluctuations in the presence of unaltered HR fluctuations may indicate an impaired control of sympathetic drive to resistance vessels compared with WKY. Note that in young SHR, hypertension also cannot be detected by conventional measurement. Fluctuations in ABP in WKY may reflect an optimal level of sympathetic activity; reduction in fluctuations may be associated with an increase or decrease in sympathetic activity at the vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Spectral analysis of the EEG in children during the introduction of antiepileptic therapy with valproic acid.

The EEGs of 16 newly diagnosed children with primary generalized epilepsy were examined before and during up to 3 years of antiepileptic therapy with valproic acid. Spectral analysis was performed and parameters of the relative power within the conventional frequency bands were compared with norm data. Before treatment no significant differences of the background activity between epileptic children and healthy controls were found. While treatment was able to reduce seizures and spike-wave activity, EEG parameters did not change systematically. There was no relation between valproate serum levels and parameters of the background activity.

Adolescent↗
PubMed1977

Spectral analysis of mouse EEG after the administration of N,N-dimethyltryptamine.

Mice were implanted with permanent cortical electrodes. The EEG was recorded during the sleep-wake cycle and after the administration of N,N-dimethyltryptamine (DMT). Based upon spectral analysis the EEG was classified into three categories: awake, slow-wave sleep (SWS), and rapid eye movement sleep (REM). The dominant frequencies were located below 2 Hz in the case of SWS and between 6 and 9 Hz for REM. When DMT was administered intraperitoneally at 20 or 40 mg/kg, a dose-dependent hypersynchrony at 2.5-4.5 Hz was always observed lasting for up to 60 min. Hypersynchronous activity in the same range was occasionally observed during awake. In this range DMT induced a different but unique frequency for each animal. This individual frequency was closely reproduced by repeated administrations of DMT to the same animal.

Animals↗