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At least 1,099 records · Page 61Linked to original sources
PubMed1996

Changes in R-R variability before and after endurance training measured by power spectral analysis and by the effect of isometric muscle contraction.

The long-term conditioning effects of physical training on cardiorespiratory interaction in 11 young healthy males were studied. Significant increases in maximum oxygen uptake (VO2max) (P < 0.05) and decreases in heart rate (P < 0.05) were achieved in all subjects following a 6-week training programme consisting of cycling for 25 min each day at a work level that increased heart rate to 85% of maximum. Heart rate variability, measured as the differences between the maximum and minimum R-R interval in a respiratory cycle, increased in nine of the subjects and decreased in two. The respiratory-cycle-related high-frequency peak in the power spectral plot of R-R variability also showed significant increases in the same nine subjects and decreases in two. The latter result was similar after normalisation of the data for changes in heart rate by calculating the common coefficient of variance [symbol: see text], where HF is the high-frequency component of the power spectral plots, using a further measure of vagal tone it was shown that, for all subjects, the R-R interval change in response to isometric contractions of the arm flexors in one respiratory cycle were significantly greater after training. These data suggest that cardiac vagal tone is increased by aerobic training for all subjects and that this is accompanied by a respiratory sinus arrhythmia (RSA) in most, but may be associated with a decrease in RSA in subjects with a very low (< 50 beats.min-1 heart rate.

Adult↗
PubMed1991

Power spectral analysis of EEG during sufentanil infusion in humans.

The purpose of this study was to examine the relationship of continuous sufentanil infusion (0.71 micrograms.kg-1.min-1 for 14 min) and the response of the power spectrum of the electroencephalogram (EEG) performed during the induction of anaesthesia in 12 patients undergoing CABG surgery. Data were collected at various times including the preinduction period, every minute during the infusion period (minute 0 to 14), and 15, 20 and 25 min after the start of the infusion (1, 6 and 11 min respectively after completion of the infusion). Within three minutes of the sufentanil infusion, the total power and the relative power of delta increased to near maximum, while the 95% spectral edge and the mean frequency decreased markedly. In spite of the continued infusion of sufentanil, there were very little further changes in the EEG activity. This ceiling effect for the EEG changes appear to coincide with the failure to respond to verbal command. We conclude that the power spectrum of the EEG failed to respond to increasing doses of sufentanil during its infusion after the rapid initial changes.

Alpha Rhythm↗
PubMed1990

Selection of the order of autoregressive models for spectral analysis of Doppler ultrasound signals.

Autoregressive modelling includes a model identification procedure, that is, it is necessary to choose the order of the autoregressive (AR) process that best describes the given finite record (frame) of the signal. Four previously suggested procedures to choose the "best order" of AR processes have been tested: The "first zero crossing" of the autocorrelation function (FZC), the "final prediction error" (FPE), "Akaike's information criterion" (AIC), and the "criterion autoregressive transfer-function" (CAT). It was found that: (i) For more than 98% of the 1280 frames of Doppler signals analyzed the order selected by the various criteria was ten or less. (ii) For the same records of Doppler signals, FPE, AIC and CAT behave in a very similar manner, but the FZC criterion underestimates the order in relation to the others. (iii) For true AR processes, the order selected is frequently different from the true AR order when frames of 64 samples are used. When more samples are used FPE, AIC and CAT tend to select the correct order. (iv) The effect on the spectral estimate of using too high a model order is usually insignificant, while using too low an order can change the estimate more dramatically, that is, overestimating the model order is better than underestimating it.

Analysis of Variance↗
PubMed2000

Spectral analysis of stereo-electroencephalograms: preictal slowing in partial epilepsies.

A substantial challenge in epileptology consists of reliable seizure anticipation ahead in time (minutes). We propose a procedure which derives from our demonstrating here that seizure outbreak shares the pretransitional behaviour characterizing nonequilibrium phase transitions with instabilities found in a number of domains. We investigated stereo-electroencephalograms, using chronically implanted cerebral electrodes, and found preictal (that is, preseizure) slowing. The method employed rests on reconstructing a high-dimensional phase orbit, projecting the orbit back to a scalar time series, namely Lerner's density function which is shown here to play the role of an order parameter, and Fourier-transforming the latter. This reduces the problem to comparing spectral characteristics of interictal and preictal states. The preictal states behaved alike for temporal-lobe and frontal-lobe partial seizures, as well as for the one subclinical temporal-lobe seizure studied. These signs of universality are in accordance with nonequilibrium phase-transitions being in essence the amplification up to a macroscopic size of fluctuations, which may be conjectured here to consist of synchronized neuronal assemblies.

Electroencephalography↗
PubMedDate not supplied

Effects of sleep deprivation on performance and EEG spectral analysis in young adults.

Nine totally sleep deprived (TSD) and nine control subjects were evaluated with a complete battery for attention and memory performance. Frontal and temporal EEGs (5 min, eyes closed) were also recorded before and after the night. TSD subjects exhibited three performance deficits: learning the Pursuit Rotor Task, implicit recall of paired words, and distractibility on the Brown-Peterson Test. Relative to evening recordings, control subjects showed decreased morning absolute powers in all electrodes for all frequencies except for Frontal delta; TSD subjects showed increased Frontal and Temporal theta and Frontal beta. These results show that motor procedural, implicit memory, and working memory are sensitive to one night of TSD, and that Frontal and Temporal theta spectral power seem to discriminate between a night with sleep from a night without.

Adult↗
PubMed2003

Regulation of human cutaneous circulation evaluated by laser Doppler flowmetry, iontophoresis, and spectral analysis: importance of nitric oxide and prostaglandines.

Nitric oxide (NO) and prostaglandines (PGs) are important in regulation of vascular tone and blood flow. Their contribution in human cutaneous circulation is still uncertain. We inhibited NO synthesis by infusing N(G)-monomethyl-L-arginine (L-NMMA) in the brachial artery (16 micromol/min for 5 min) and reversed it by intraarterial infusion of L-arginine (40 micromol/min for 7.5 min). PG synthesis was inhibited by the cyclooxygenase inhibitor aspirin (600 mg over 5 min intravenously). Basal cutaneous perfusion and perfusion responses during iontophoresis with the endothelium-dependent vasodilator acetylcholine (ACh) and the endothelium-independent vasodilator sodium nitroprusside (SNP) were recorded by laser Doppler flowmetry (LDF). We performed wavelet transforms of the measured signals. Mean spectral amplitude within the frequency interval from 0.0095 to 1.6 Hz and mean and normalized amplitudes of five intervals around 1, 0.3, 0.1, 0.04, and 0.01 Hz were analysed. The oscillations with frequencies around 1, 0.3, 0.1, and 0.04 Hz are influenced by the heartbeat, the respiration, the intrinsic myogenic activity of vascular smooth muscle, and the neurogenic activity of the vessel wall, respectively. We have previously shown that the oscillation with a frequency around 0.01 Hz is modulated by the vascular endothelium. L-NMMA reduced mean value of the LDF signal by approximately 20% (P = 0.0067). This reduction was reversed by L-arginine. Mean value of the LDF signals during ACh and SNP iontophoresis did not change after infusion of L-NMMA. Aspirin did not affect mean value of the LDF signal or the LDF signal during ACh or SNP iontophoresis. Before interventions the only significant difference between the effects of ACh and SNP was observed in the frequency around 0.01 Hz, where ACh increased normalized amplitude to a greater extent than SNP. L-NMMA abolished this difference, whereas it reappeared after infusion of L-arginine (P = 0.0084). Aspirin did not affect this difference (P = 0.006). We conclude that basal cutaneous blood flow and the endothelial dependency of the oscillation around 0.01 Hz are partly mediated by NO, but not by endogenous PGs. Other aspects of human cutaneous circulation studied are not regulated by NO or PGs.

Acetylcholine↗
PubMed2006

Real time spectral analysis during phytochrome chromophore and chromoprotein purification.

The plant photoreceptor phytochrome senses light quality and quantity in the red region of the spectrum, directing adaptation and development. The functional holo-protein is a dimeric chromoprotein which is formed by an autoassembly reaction between the translation product and the open chain tetrapyrroles phytochromobilin (PPhiB) or phycocyanobilin (PCB). We are interested in structure/function relationships within the phytochrome molecule, in particular chromophore/protein interaction during the assembly and photoactivation, using IR and NMR spectroscopy. For this we use an automated F/HPLC system running in a darkroom to purify large amounts of protein and chromophore separately. To obtain highly pure PCB chromophore we developed improved extraction and purification methods in which the final step is RPC-18 HPLC. As there are many spectrally only slightly different tetrapyrroles in the extract, the triple-wavelength monitoring offered by the F/HPLC detector was inadequate for distinguishing between PCB and impurities. Furthermore, lambda(max) for the phytochrome Pfr signalling state lies between 705 and 730 nm, beyond the range of the detector. Also, as both holo-protein and chromophore are photoactive, we wished to minimize light exposure of the eluate. We therefore implemented a miniature CCD-based flow UV-vis spectrophotometer using a xenon flash and quartz fiber optics enabling us monitor the entire 250-800 nm spectrum of the eluate to an accuracy of +/-3 x 10(-3)A in real time. The instrumentation described can be added to any chromatographic system, thereby allowing the purification of any molecule to be monitored easily and efficiently.

Bacterial Proteins↗
PubMed1997

Characterisation of atherosclerotic plaque by spectral analysis of intravascular ultrasound: an in vitro methodology.

Raw 30-MHz intravascular ultrasound data have been captured from postmortem coronary arteries (n = 4) to develop radio frequency analysis techniques for the characterisation of atherosclerotic plaque. Digitised data acquired from positions (n = 8) within diseased sections of artery were compared with the corresponding histology and radiology. Scan-converted images were used to locate regions of interest (ROI = 33) within areas of tissue composition: loose fibrotic tissue (LFT), dense fibrotic tissue (DFT) and calcium (CA). A range of parameters was extracted from the normalised power spectrum of each ROI within the bandwidth 17-42 MHz. Significant discrimination between LFT/DFT and between LFT/CA was provided by maximum power and spectral slope (dBMHz-1). However, the greatest discriminative power was given by the y-axis (0 Hz) intercept of the spectral slope: LFT/DFT (p = 0.001); LFT/CA (p = 0.0001); and DFT/CA (p = 0.089).

Coronary Artery Disease↗
PubMed2000

Classification of arterial plaque by spectral analysis of in vitro radio frequency intravascular ultrasound data.

To test whether radio-frequency analysis of coronary plaques predicts the histological classification, r.f. data were collected using a 30 MHz intravascular ultrasound scanner. Two hundred ninety-nine regions-of-interest from eight postmortem coronary arteries were selected and identified by histology as falling into one of seven different tissue types. These are loose fibrous tissue (n = 78), moderate fibrous tissue (n = 27), dense fibrous tissue (n = 33), microcalcification (n = 14), calcified plaque (n = 55), lipid/fibrous mixture (n = 51) and homogeneous areas of lipid pool (n = 29). On the basis of a previous study, four spectral parameters were calculated for each of the regions-of-interest: maximum power (dB), mean power (dB), spectral slope (dB/MHz) over the bandwidth 18-35 MHz and the intercept of the spectral slope with the 0 Hz axis (dB). A minimum-distance classifier using the Mahalanobis (1948) distance was applied to the data. Following resubstitution of the training data into the classifier, the total correctly classified was 54%. The data were reclassified using three broader tissue groups: (1) calcified plaque, (2) lipid pool and (3) a mixed fibrous category, incorporating loose fibrous tissue, moderate fibrous tissue, dense fibrous tissue, lipid/fibrous mixture and microcalcification. The total correctly classified was 86%. Using "leave-one-out" cross-validation, the classification rates were 48% for seven tissue subgroups and 83% for three broader categories of tissue type.

Cadaver↗
PubMed1996

A computer algorithm to impute interrupted heart rate data for the spectral analysis of heart rate variability--the ARIC study.

The shorter term beat-to-beat heart rate data collected from the general population are often interrupted by artifacts, and an arbitrary exclusion of such individuals from analysis may significantly reduce the sample size and/or introduce selection bias. A computer algorithm was developed to label as artifacts any data points outside the upper and lower limits generated by a 5-beat moving average +/- 25% (or set manually by an operator using a mouse) and to impute beat-to-beat heart rate throughout an artifact period to preserve the timing relationships of the adjacent, uncorrupted heart rate data. The algorithm applies Fast Fourier Transformation to the smoothed data to estimate low-frequency (LF; 0.025-0.15 Hz) and high-frequency (HF; 0.16-0.35 Hz) spectral powers and the HF/LF ratio as conventional indices of sympathetic, vagal, and vagal-sympathetic balance components, respectively. We applied this algorithm to resting, supine, 2-min beat-to-beat heart rate data collected in the population-based Atherosclerosis Risk in Communities study to assess the performance (success rate) of the algorithm (N = 526) and the inter-and intra-data-operator repeatability of using this computer algorithm (N = 108). Eighty-eight percent (88%) of the records could be smoothed by the computer-generated limits, an additional 4.8% by manually set limits, and 7.4% of the data could not be processed due to a large number of artifacts in the beginning or the end of the records. For the repeatability study, 108 records were selected at random, and two trained data operators applied this algorithm to the same records twice within a 6-month interval of each process (blinded to each other's results and their own prior results). The inter-data-operator reliability coefficients were 0.86, 0.92, and 0.90 for the HF, LF, and HF/LF components, respectively. The average intra-data-operator reliability coefficients were 0.99, 0.99, and 0.98 for the HF, LF, and HF/LF components, respectively. These results indicate that this computer algorithm is efficient and highly repeatable in processing short-term beat-to-beat heart rate data collected from the general population, given that the data operators are trained according to standardized protocol.

Algorithms↗
PubMed1984

Spectral analysis of kindled hippocampal afterdischarges in lead-treated rats.

Male rats were exposed to lead from parturition through weaning. When subjected to electrical hippocampal kindling as adults, although there were no alterations in the kindling rates, lead-treated animals were found to differ from controls in several other respects. In contrast to controls, lead-treated animals did not show an increase in afterdischarge (AD) duration with kindling, and the power spectrum of the AD did not shift to a higher peak frequency. There was a clear dose-related effect of lead on the spectra of the kindled AD, which in lead-treated groups was characterized by greater power in the low-frequency bands. These data indicate that long-lasting dysfunction can occur following a brief neonatal lead exposure. Power spectral techniques may be useful for future studies in neurotoxicology and epilepsy.

Animals↗
PubMed1990

Spectral analysis and acoustic transmission of mitral and aortic valve closure sounds in dogs. Part 4: Effect of modulating cardiac inotropy.

A surgical protocol was designed to implant in dogs a programmable atrioventricular pacemaker and to destroy the bundle of His with one to four 0.1 ml formaldehyde injections. The heart rate and P-R interval were paced at 100 beats min-1 and 75 ms, respectively. Cardiac inotropy was then varied in five animals by using injections or infusions of cardiotonic drugs (Dobutamine, Betalol and Quinidine). Their effect on the spectra and acoustic transmission of the mitral M1 and aortic A2 closure sound components produced within the left heart and transmitted up to the body surface was studied. Results indicate that changes in cardiac inotropy strongly modify the intensity of M1 and A2 but do not markedly affect their spectral distribution. They also affect the transfer function of the heart/thorax acoustic system, but this influence is small compared with that of a 12 min reference interval. In addition, it was shown that the intensity of M1 is more sensitive to the cardiotonic agents than the intensity of A2.

Animals↗
PubMedDate not supplied

Power spectral analysis of EEG activity obtained from cortical and subcortical sites during the vigilance states of the cat.

There is considerable evidence that the raphé system and the region of the nucleus tractus solitarious (NTS), including the area postrema, play significant roles in slow-wave sleep mechanisms and in EEG synchronization. Studies of the interactions between these systems and the neocortex are much needed. If neuronal activity in these lower brainstem regions regulates the degree of cortical synchrony then a high degree of correspondence between the EEG of the area postrema or raphé complex with that of the cortex might be expected. In order to quantitate the reequency characteristics of the EEG obtained from these subcortical sites (nucleus raphé dorsalis, area postrema, as well as anatomical controls adjacent to these regions) during the different vigilance states (waking, slow-wave sleep, REM sleep) in the cat, power spectral analyses techniques were employed. Comparison of these subcortical spectral characteristic with those obtained from cortical (frontal and occipital) sites during the same vigilance state, show that the spectral measures elicited from the region of the area postrema closely correspond to that of the cortex, particularly during slow-wave sleep. On the other hand, the EEG of the anterior portion of the raphé region, although exhibiting a substantial low frequency component during slow-wave sleep in comparison to wakefulness does not show a statistically significant shift to low frequencies such as occurs in the area postrema or the cortex. These results suggest that the increases in the low frequency content of the cortical EEG sites during slow-wave sleep results from synchronizing inputs from the area postrema to a greater extent than from the raphé complex.

Animals↗
PubMed1988

Spectral analysis of heart rate variability following human heart transplantation: evidence for functional reinnervation.

To determine the status of innervation in long-term human donor allografts, the power spectrum of heart rate variability was analysed in 9 post-transplant patients and 7 healthy control subjects. The mean post-transplant follow-up was 17.8 months (range: 2-37 months). Continuous ECG signals were recorded throughout a 15-min rest period. An R-R interval tachogram was generated and an autoregressive model using linear predictive coding, was applied to the heart rate variability data. In 8 transplant patients the frequency oscillations were irregular, broad based and widely dispersed from 0 to 1 Hz. The patterns resembled white noise and were consistent with dissociation of the donor allograft from the recipient's central nervous system. In contrast, one patient displayed a heart rate variability spectrum indistinguishable from that of control subjects. This pattern contained two distinct spectral bands; one corresponding to the patient's respiratory rate at 0.2 Hz and a low frequency Mayer wave at 0.1 Hz. Atropine abolished the respiratory (vagal) peak. Except for this patient's post-transplant time (33 months compared to the group mean of 17.6 months), there were no clinical characteristics which distinguished this patient from the others. While the mean heart rate for the remaining 8 allografts was significantly higher than controls (95.3 vs 64.5 bt/min; P less than 0.001) the standard deviation of heart rate variability for the 8 patients was significantly narrower than controls (0.7 vs 4.86; P less than 0.01). The variance of heart rate for the patient with the normal power spectrum was fourfold greater than the mean SD of the other transplant patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Two-dimensional fluorescence correlation spectroscopy II: spectral analysis of derivatives of anthracene and pyrene in micellar solutions.

Generalized two-dimensional (2D) correlation spectroscopy has been applied to the analysis of fluorescence spectra in two micellar systems: (1) a mixture of pyrene and 1,3,6,8-pyrenetetrasulfonic acid in the cationic micellar solutions of cetyltrimethylammonium chloride (CTAC) and (2) a mixture of pyrene and 9-anthracencepropionic acid in anionic micellar solutions of sodium dodecyl sulfate (SDS). Fluorescence quenching is employed as a perturbation mode for causing intensity changes in fluorescence bands (quenching perturbation). Iodide ion (I-) is used as a quencher in the former system, and cetyl pridinium chloride (CPC) is used in the latter. Vibronic bands in the complicated fluorescence spectra of the mixture of the analytes were successfully resolved. It is shown that asynchronous maps are especially useful for spectral resolution enhancement when the quenching perturbation is employed in 2D fluorescence correlation spectroscopy. Furthermore, the information about the order of response of the bands to quenching is obtained by comparing the signs of synchronous and asynchronous cross-peaks.

Anthracenes↗
PubMed1993

Spectral analysis of heart rate variability in athletes.

The objectives of the study were to characterize power spectrum pattern of the heart rate variability and assessment of the relative contributions of sympathetic and parasympathetic cardiac nervous system control in athletes. Thirty-three male athletes, swimming (1), canoeing (10), cycling (6), athletics (4), football (3), roller-skating (2) and volleyball (7) aged 23.4 +/- 5.5 years, with a mean athletic level of 18 hours/week (8-45) and 33 sedentary healthy control subjects were included. Ecg signals were recorded after a period of 15 minutes in supine rest with controlled breathing at 15 cycles/min. Signal acquisition was done at 300 samples/sec. From 512 consecutive heart beats, we calculated mean average, standard deviation, maximum and minimum R-R intervals and, after computing the fast Fourier transform, total spectrum power, low frequency (LF), high frequency (HF) components and its ratio (LF/HF). The average R-R interval was 987.7 +/- 168.8 ms and 762.7 +/- 125.3 ms, the variance was 5.44 and 2.51 ms2 and ratio of R-R interval maximum/minimum (E/I ratio) 1.53 +/- 0.16 and 1.41 +/- 0.16, respectively for athletes and control group. Differences between groups were significant (p < 0.01) for all parameters, with higher variability in the athletes. Both spectral bands (LF and HF) had higher power in athletes (LF = 925 +/- 920 and HF = 2258 +/- 2349 ms2) than in the control group (LF = 442 +/- 446 and HF = 1179 +/- 1542 ms2) (p < 0.01). There were no significant differences for LF/HF ratio, or normalized LF (LF%) or normalized HF (HF%) between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2005

Spectral analysis of blood perfusion in the free latissimus dorsi myocutaneous flap and in normal skin.

To find the properties in the oscillatory components of the cutaneous blood flow on the successful free flap, a wavelet transform was applied to the laser Doppler flowmetry (LDF) signals which were measured simultaneously on the surfaces of the free latissimus dorsi myocutaneous flap and on the adjacent intact skin of the healthy limb, of 18 patients. The frequency interval from 0.0095 to 1.6 Hz was examined and was divided into five subintervals (I: 0.0095-0.021 Hz; II: 0.021-0.052 Hz; III: 0.052-0.145 Hz; IV: 0.145-0.6 Hz and V: 0.6-1.6 Hz) corresponding to endothelial metabolic, neurogenic, myogenic, respiratory and cardiac origins. The average amplitude and total power in the frequency range 0.0095-1.6 Hz as well as within subintervals I, II, IV and V were significantly lower for signals measured on the free flap than those obtained in the healthy limb. However in interval III, they were significantly higher. The normalized spectral amplitude and power in the free flap were significantly lower in only two intervals, I and II, yet in interval III they were significantly higher; no statistical significance was observed in intervals IV and V. The distinctive finding made in this study, aside from the decrease of endothelial metabolic processes and sympathetic control, was the significant increase of myogenic activity in the free flap. It is hoped that this work will contribute towards knowledge on blood circulation in free flaps and make the monitoring by LDF more reliable.

Adolescent↗
PubMed1990

Spectral analysis and acoustic transmission of mitral and aortic valve closure sounds in dogs. Part 3. Effects of altering heart rate and P-R interval.

A surgical protocol was designed to implant, in seven dogs, a programmable sequential atrioventricular pacemaker after destruction of the bundle of His to produce a chronic heart block. The heart rate and P-R interval were then varied independently and their influence on the spectra and acoustic transmission of the mitral M1 and aortic A2 valve closure sounds was studied. Results indicate that the major effects of varying the P-R interval are a strong change in the intensity of M1 and modifications of its acoustic transmission across the heart/thorax acoustic system. No similar influence is observed on the intensity and acoustic transmission of A2. Varying the heart rate has a small effect of the intensity of M1 but none on the intensity of A2. In addition, changes in either the P-R interval or the heart rate do not seem to modify the spectral profile of the intracardiac and thoracic M1 and A2 components.

Animals↗