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At least 595 records · Page 33Linked to original sources
PubMed2004

Spectral analysis of the electromyograph of the erector spinae muscle before and after a dynamic manual load-lifting test.

The aim of the present study was to assess the spectral behavior of the erector spinae muscle during isometric contractions performed before and after a dynamic manual load-lifting test carried out by the trunk in order to determine the capacity of muscle to perform this task. Nine healthy female students participated in the experiment. Their average age, height, and body mass (+/- SD) were 20 +/- 1 years, 1.6 +/- 0.03 m, and 53 +/- 4 kg, respectively. The development of muscle fatigue was assessed by spectral analysis (median frequency) and root mean square with time. The test consisted of repeated bending movements from the trunk, starting from a 45 masculine angle of flexion, with the application of approximately 15, 25 and 50% of maximum individual load, to the stand up position. The protocol used proved to be more reliable with loads exceeding 50% of the maximum for the identification of muscle fatigue by electromyography as a function of time. Most of the volunteers showed an increase in root mean square versus time on both the right (N = 7) and the left (N = 6) side, indicating a tendency to become fatigued. With respect to the changes in median frequency of the electromyographic signal, the loads used in this study had no significant effect on either the right or the left side of the erector spinae muscle at this frequency, suggesting that a higher amount and percentage of loads would produce more substantial results in the study of isotonic contractions.

Adult↗
PubMed1975

Preparative method for gas chromatographic/mass spectral analysis of trace quantities of pesticides in fish tissue.

A large capacity, low efficiency pesticide cleanup method is combined with a small capacity, high efficiency method for gas chromatographic/mass spectral analysis of fish tissue. Trace chemicals are extracted from the tissue, removed from the bulk of the co-extracted lipids through selective desorption from Micro Cel-E, and isolated from the remaining lipids by gel permeation chromatography. The procedure is capable of cleaning up the extract from several hundred grams of fish, minimizes sample contamination, and permits identification of xenobiotic chemicals present at ng/g concentrations.

Chromatography, Gas↗
PubMed1992

Spectral analysis of heart rate dynamics in elderly persons with postprandial hypotension.

Prior studies suggest that postprandial hypotension in elderly persons may be due to defective sympathetic nervous system activation. We examined autonomic control of heart rate (HR) after a meal using spectral analysis of HR data in 13 old (89 +/- 6 years) and 7 young (24 +/- 4 years) subjects. Total spectral power, an index of overall HR variability, was calculated for the frequency band between 0.01 and 0.40 Hz. Relatively low-frequency power, associated with sympathetic nervous system and baroreflex activation, was calculated for the 0.01 to 0.15 Hz band. High-frequency power, representing parasympathetic influences on HR, was calculated for the 0.15 to 0.40 Hz band. Mean arterial blood pressure declined 27 +/- 8 mm Hg by 60 minutes after the meal in elderly subjects, compared with 9 +/- 8 mm Hg in young subjects (p less than or equal to 0.0001, young vs old). The mean change in low-frequency HR power from 30 to 50 minutes after the meal was +19.4 +/- 25.3 U in young subjects versus -0.1 +/- 1.5 U in old subjects (p less than or equal to 0.02). Mean change in total power was also greater in young (19.0 +/- 26.6 U) subjects compared with old subjects (0.0 +/- 1.6 U, p greater than or equal to 0.02). Mean ratio of low:high-frequency power increased 3.1 +/- 3.3 U in young subjects vs 0.5 +/- 2.7 U in old subjects (p less than or equal to 0.01). The increase in low-frequency HR power and in the low:high frequency band ratio in young subjects is consistent with sympathetic activation in the postprandial period.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

Spectral analysis of intercycle heart fluctuations in the diethyl-ether-anaesthetized or pithed rat treated with prazosin, dl-propranolol, endothelin-1, alpha-r atriopeptin and ACE-inhibitors.

1. Frequency-domain spectral analysis of stationary ECG R-R intervals was made by fast Fourier transformation (FFT) in conditions of monitored arterial blood pressure and respiratory activity in diethyl-ether-anaesthetized and pithed adult rats. This technique yields a number of parameters which allow quantitative evaluation of the non-random distribution of the mean values obtained in time-domain studies. The frequency-analysis method enables the overall heart rate variability to be broken down into its various constituents, which are differently affected by physiological loading and capable of selective reactivity to pharmacological agents. 2. The low-frequency spectral component obtained by breaking down the total spectral density power, i.e. the appropriate variability signal (band width < 0.15 Hz) and a higher-frequency band corresponding to spontaneous (0.80-1.60 Hz) or artificially imposed (0.75 Hz) respiratory activity were estimated and their integrated areas evaluated as absolute powers or normalized fractional values. 3. The power of the high-frequency spectral component increased in all animal preparations under treatment with prazosin, dl-propranolol, endothelin-1 and the angiotensin converting enzyme (ACE) inhibitors captopril, lisinopril, quinapril and ramipril. The power of the low-frequency band increased under alpha-r atriopeptin and ACE inhibitors in the pithed preparations only, and decreased in the anaesthetized animals. 4. The new power spectrum features and trends detected indicate that these time-independent, model-dependent cardiovascular and respiratory markers are subject to some form of complex peptidergic control. 5. The relative roles of the various factors operating in the genesis of these short-term changes in spectral power in the low- and high-frequency bands cannot be interpreted as indicating a reciprocal push-pull relationship between sympathetic and parasympathetic control. 6. The study findings, however, can be interpreted as providing evidence of a different and to some extent alternative form of integrative cardiovascular control persisting in the pithed rats (i.e. in the 'peripheral', CNS-destroyed preparations). 7. New areas of theoretical and applied research are being developed in the (auto)classification of (iso)receptors and drug analogues through exploration of multiple physiological and pharmacokinetic parameters in the frequency-domain. Furthermore, model-independent frequency-domain methods not requiring stationary data will afford scope for even more significant developments by separating the overlapping dynamic processes from a whole series of correlated effects.

Animals↗
PubMed2001

[Spectral analysis of heart rate responses to light and color stimulation of the cerebral hemispheres].

To study changes autonomic nervous function at differential light stimulations of the brain hemispheres in 126 healthy persons stimulated of the right and left hemifields in retinas eyes by light of different colour. Before and after influence the spectral analysis of a heart rhythm was made. The decrease of capacity of a spectral range 0.08-0.12 Hz is revealed at red-green stimulations, that testifies to decrease baroreflex tone and range 0.15-0.5 Hz at red-green and red-violet stimulations, that testifies about vagolitical influence. The conclusion about domination of the right hemisphere in autonomic nervous function is made.

Adult↗
PubMed1998

Assessment of the sympatho-vagal interaction in central serous chorioretinopathy measured by power spectral analysis of heart rate variability.

BACKGROUND: The purpose of this study was to measure the activity of the sympathetic nervous system in patients with central serous chorioretinopathy (CSC) by power spectral analysis (PSA) of heart-rate (RR-interval) variability, a noninvasive method that reflects the balance of the sympathetic-vagal interaction. METHODS: The following four different groups of patients were measured; group 1, acute CSC (n = 11); group 2, acute recurrent CSC (n = 7); group 3, chronic persistent CSC (n = 4); group 4, complete remission of CSC (n = 9). The data recorded for these 31 patients (29 men and 2 women), with an average age of 44 years were compared with those noted for a group of 15 age-matched healthy individuals. The sympathetic-vagal balance is expressed by the ratio of the low-frequency component (LF) to the high-frequency component (HF) of the power spectrum. RESULTS: Significant differences in mean LF/HF ratios were found as follows for all but one of the sub-groups as compared with the normal controls (LF/HF = 1.1): group 1, LF/HF = 5.5 (P < 0.01); group 2, LF/HF = 5.4 (P < 0.05); group 3, LF/HF = 4.2 (P = 0.1); and group 4, LF/HF = 3.0 (P < 0.01). There was also a significant difference between active CSC and inactive CSC (P < 0.05). CONCLUSIONS: These results support the view that the pathogenesis of CSC is related to an increase in the sympathetic activity of the autonomic nervous system. Furthermore, the LF/HF ratios seem to correlate with the activity of the disease.

Acute Disease↗
PubMed2004

Polarization mapping: a method to improve sum frequency generation spectral analysis.

A "polarization mapping" method has been applied to improve the fitting quality of sum frequency generation (SFG) vibrational spectra of complicated systems and validate the data analysis of simple SFG spectra. Using such a method, two-dimensional SFG spectra can be constructed, from which more reliable spectral information can be obtained from a surface/interface. Model calculations as well as experiments have been employed to illustrate the power of the polarization mapping method for spectral analysis of SFG spectra. By using a deuterated polystyrene surface and interfacial protein molecules as examples, we demonstrate that this method is especially important for complicated molecules, such as polymers and proteins.

Journal Article↗
PubMed1989

Spectral analysis of cyclic symptoms in late luteal phase dysphoric disorder.

Fifty-eight subjects self-referred for premenstrual difficulty were evaluated for late luteal phase dysphoric disorder through a spectral analysis technique applied to prospective symptom ratings. Data from the Schedule for Affective Disorders and Schizophrenia--Life-time Version were used to group the subjects according to the absence or presence of past or present psychiatric disorders. The two psychiatric groups were compared with regard to both patterns of significant symptom change and premenstrual symptom severity. Differences between the groups are used to discuss issues regarding the reliable identification of late luteal phase dysphoric disorder and the impact of other psychiatric disorders on this syndrome.

Adult↗
PubMed1976

[Method of determining system errors due to the quality of the electronic filters in the spectral analysis of noise vibration].

A method to determine systematic errors, conditioned by the extreme degree of fading out, beyond the permeability band of electric filters used in noise and vibrations' spectral analysis, is suggested. The obtained formulas for the active filters of the noise-measuring apparatus PSI-202, making part of the hygiene network equipment throughout the country, are tabulated and thus prompt determination of the respective systematic error is rendered possible.

Acoustics↗
PubMed1991

[Role of sympathetic nervous system on blood pressure and heart rate variabilities in the rat: spectral analysis].

The role of the sympathetic nervous system (SNS) in the genesis of the beat-to-beat variability of blood pressure (BP) and heart rate (HR) was studied using spectral analysis. The SNS activity of genetically normotensive rats of the Lyon strain (LN) was abolished in 2 ways: 1) adrenergic blockade with administrations of phentolamine (PHE, 5 mg/kg i.v.) or propranolol (PRO, 5 mg/kg i.v.) or both drugs (PHEPRO) or 2) destruction of the sympathetic fibers with an early chronic treatment with guanethidine (LNSx). HR and systolic (SBP) and diastolic (DBP) BP spectra were computed using 50 to 100 stationary sequences from 1 h beat-to-beat recordings and covered the 0.015-3.85 Hz frequency band. In LN rats, spectra obtained in baseline conditions exhibited a high-frequency peak (HF, 1.04-1.13 Hz) related to the respiratory frequency and a mid-frequency peak (MF, 0.38-0.45 Hz). Concerning BP, the alterations of the SNS induced significant decreases of the total modulus (mmHg/Hz1/2) of the MF band (0.27-0.74 Hz): [formula: see text] In addition, the MF peak of SBP and DBP spectra was abolished in LNSx and PHEPRO rats. Concerning HR spectra, the moduli of all the frequency components were decreased in PHEPRO rats only. In conclusion, the similarity of the results observed in LNSx and PHEPRO rats shows that the MF oscillations of BP depend in a large extent (65%) on the action of the sympathetic fibers and involve the activation of both alpha- and beta-adrenoceptors. Concerning DBP, this effect is especially mediated by the activation of alpha-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

Spectral analysis of heart rate and blood pressure variability.

The cardiovascular system contains negative feedback and time-delay mechanisms resulting in oscillations in heart rate and blood pressure, which are apparent when these signals are measured over time. Specifically, spectral analysis and nonlinear analysis techniques allow quantification of heart rate and blood pressure variability. Alterations in heart rate and blood pressure variability as evidenced from the spectral characteristics of these physiological signals allow the clinicians to have indicators of aberrations of neural control in various conditions or when drugs such as beta blockers, adrenergic agents, methylxanthines, etc., are being administered.

Animals↗
PubMed1995

Physiology and pathophysiology of heart rate and blood pressure variability in humans: is power spectral analysis largely an index of baroreflex gain?

1. It is often assumed that the power in the low- (around 0.10 Hz) and high-frequency (around 0.25 Hz) bands obtained by power spectral analysis of cardiovascular variables reflects sympathetic and vagal tone [corrected] respectively. An alternative model attributes the low-frequency band to a resonance in the control system that is produced by the inefficiently slow time constant of the reflex response to beat-to-beat changes in blood pressure effected by the sympathetic (with or without the parasympathetic) arm(s) of the baroreflex (De Boer model). 2. We have applied the De Boer model of circulatory variability to patients with varying baroreflex sensitivity to patients with varying baroreflex sensitivity and one normal subject, and have shown that the main differences in spectral power (for both low and high frequency) between and within subjects are caused by changes in the arterial baroreflex gain, particularly for vagal control of heart rate (R-R interval) and left ventricular stroke output. We have computed the power spectrum at rest and during neck suction (to stimulate carotid baroreceptors). We stimulated the baroreceptors at two frequencies (0.1 and 0.2 Hz), which were both distinct from the controlled respiration rate (0.25 Hz), in both normal subjects and heart failure patients with either sensitive or poor baroreflex control. 3. The data broadly confirm the De Boer model. The low-frequency (0.1 Hz) peak in either R-R or blood pressure variability) was spontaneously generated only if the baroreflex control of the autonomic outflow was relatively intact.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

EEG spectral analysis during hypnotic induction, hypnotic dream and age regression.

EEG was recorded monopolarly at frontal (F3, F4), central (C3, C4) and posterior (in the middle of O1-P3-T5 and O2-P4-T6 triangles) derivations during the hypnotic induction of the Stanford Hypnotic Clinical Scale (SHCS) and during performance following suggestions of hypnotic dream and age-regression as expressed in the before-mentioned scale. 10 low-hypnotizable and 9 highly-hypnotizable and right-handed female students participated in one experimental session. Evaluations were Fast-Fourier spectral analyses during the following conditions: waking-rest in eyes-open and eyes-closed condition; early, middle, and late phases of hypnotic induction; rest-hypnosis in eyes closed condition; hypnotic dream and age regression. After spectral analysis of 0 to 44 Hz, the mean spectral amplitude estimates across seven Hz bands (theta 1, 4-6 Hz, theta 2, 6-8 Hz; alpha 1, 8-10 Hz; alpha 2, 10-13 Hz; beta 1, 13-16 Hz; beta 2, 16-20 Hz; beta 3, 20-36 Hz) and the 40-Hz EEG band (36-44 Hz) for each experimental condition were extracted. In eyes-open and -closed conditions in waking and hypnosis highly-hypnotizable subjects produced a greater 40-Hz EEG amplitude than did low hypnotizable subjects at all frontal, central and posterior locations. In the early and middle hypnotic induction highly-hypnotizables displayed a greater amount of beta 3 than did low hypnotizables and this difference was even more pronounced in the left hemisphere. With posterior scalp recordings, during hypnotic dream and age regression, high hypnotizables displayed, as compared with the rest-hypnosis condition, a decrease in alpha 1 and alpha 2 amplitudes. This effect was absent for low hypnotizables. Beta 1, beta 2 and beta 3 amplitudes increased in the left hemisphere during age regression for high hypnotizables; low hypnotizables, in contrast, displayed hemispheric balance across imaginative tasks. High hypnotizables during the hypnotic dream also displayed in the right hemisphere a greater 40-Hz EEG amplitude as compared with the left hemisphere. This difference was even more evident for posterior recording sites. This hemispheric trend was not evidenced for low hypnotizable subjects. Theta power was never a predictor of hypnotic susceptibility, 40-Hz EEG amplitude displayed a very high main effect (p < 0.004) for hypnotizability in hypnotic conditions by displaying a greater 40-Hz EEG amplitude in high hypnotizables with respect to lows.

Adult↗
PubMed1997

Evaluation of cancellous structure in the distal radius using spectral analysis.

A preliminary study was conducted to analyze trabecular patterns in digitized wrist radiographic images from 68 patients (31 males and 37 females), aged from 7 to 93 years. The fast Fourier transform was used to perform the spectral analysis of the distal radius. Three indices were defined to permit quantification of the cancellous structure in terms of the spacing and orientation of bone trabeculae (periodicity): a spectral trabecular index, a longitudinal trabecular index, and a transverse trabecular index. The spectral trabecular index reflects the periodicity of the trabeculae (spacing and orientation), while the other 2 selectively reflect the periodicity of longitudinally and transversely oriented ones. The ratio of the longitudinal and transverse trabecular indices was also studied. The shape of the high magnitude frequencies in the spectrum was crosslike for all patients, implying a preferentially orthogonal 2-dimensional structure for the cancellous bone in the distal end of the radius. The variation of the defined trabecular bone indices with age corresponded with the formation of bone through infancy and adolescence, reaching a peak in adulthood and gradual loss thereafter. This quantification detects structural changes that occur with aging and may therefore be useful in the study of osteoporosis.

Adolescent↗
PubMed1998

Cross-spectral analysis of physiological tremor and muscle activity. II. Application to synchronized electromyogram.

We investigated the relationship between synchronized muscle activity and tremor time series in (enhanced) physiological tremor by cross-spectral analysis. Special attention was directed to the phase spectrum and its potential to clarify the contribution of reflex mechanisms to physiological tremor. The phase spectra are investigated assuming that the electromyogram (EMG) synchronization was caused by a reflex or a central oscillator. Comparing these results to phase spectra of measured data, we found a significant contribution of reflexes. But reflexes only modify existing peaks in the power spectrum. The main agents of physiological tremor are an efferent pace and the resonant behavior of the biomechanical system.

Biomechanical Phenomena↗
PubMed2001

Autonomic profile under hypnosis as assessed by heart rate variability and spectral analysis.

To test the hypothesis of a sympathovagal balance shift towards an enhanced vagal tone under the condition of a standardized hypnosis, we used the assessment of heart rate variability including spectral analysis in 10 healthy subjects (5 female, 5 male, age ranging from 27 to 42 years). We compared the subjects under baseline condition (resting) and under hypnosis, measured on a different day, for a measuring period of five minutes for each condition. The result was reduced total power in the low frequency band (0.01-0.05 Hz) reflecting sympathetic activity. Also, the ratio of low to high frequency power (LFIHF) was reduced when under hypnosis. This reduction was due to a reduced LF component, but only a slightly reduced mid frequency component. With considerable variability, we also found activated mid frequency bands (0.05-0.15Hz) under hypnosis, likely reflecting baroreceptor activity. We conclude that the autonomic status in hypnosis is associated with a change towards reduced low frequency activity, but not necessarily with enhanced high frequency activity.

Adult↗
PubMed1996

Power spectral analysis for autonomic influences in heart rate and blood pressure variability in fetal lambs.

Variability of R-R intervals and arterial blood pressure signals in chronically instrumented fetal lambs was analyzed by power spectral analysis based on an assumption of maximum entropy. There were four consistent components, very low (VL, 0.01-0.025 cycle/beat), low (L, 0.025-0.125 cycle/beat), middle (M, 0.125-0.2 cycle/beat), and high (H, 0.2-0.5 cycle/beat), in the normal heart rate variability and blood pressure spectra. Integrated peaks in the power spectrum were compared before and after the administration of sympathetic and parasympathetic blockades. beta-Sympathetic blockade reduced the spectral power in the VL and L frequency components. alpha-Sympathetic blockade reduced only the M frequency component in the spectrum of R-R interval variability. Parasympathetic blockade reduced the H and L frequency components in the R-R interval variability spectrum but increased these components in the systolic blood pressure variability spectrum. The results clearly demonstrate the association between fetal autonomic activity and change of power spectrum of heart rate and blood pressure variability.

Animals↗
PubMed2001

Power spectral analysis of the electroencephalogram during induced total spinal block.

PURPOSE: To evaluate the effects of total spinal block (TSB) on brain function, TSB-induced changes in cortical electrical activities were analyzed using power spectral analysis of an electroencephalogram (EEG). METHODS: Six patients suffering from chronic pain who were undergoing TSB therapy were studied. TSB was established with intrathecal 1% lidocaine (0.3 ml.kg(-1)) injected through the C1-2 lateral intervertebral space. Mechanical ventilation was continued via a laryngeal mask until the recovery of respiration. The EEG recording was started before TSB induction and continued until 10 min after extubation. The following processed EEG parameters were monitored: spectral edge frequency-90% (SEF90), spectral median frequency (SMF), and relative power in the frequency bands of delta, theta, alpha, beta, and the delta ratio [(alpha + beta)/delta]. RESULTS: TSB induced an unconscious state more than 40 min in all patients. During TSB, 12-13 Hz in SEF90 and 6-7 Hz in SMF were observed. These values are consistent with the previously reported prearousal threshold from general anesthesia. The other EEG descriptors did not change during the TSB-induced unconscious state. CONCLUSION: The dissociation of cortical electrical activities and the clinical coma-like condition may be characteristic of the TSB-induced unconscious state.

Journal Article↗