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Spectral Components (spectral + component)
Selected AbstractsEPR Analysis of n -Butyl Acrylate Radical PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2009Johannes Barth Abstract Via electron paramagnetic resonance (EPR) spectroscopy, concentrations of secondary propagating radicals (SPRs) and tertiary mid-chain radicals (MCRs) in n -butyl acrylate solution polymerization were measured. The EPR spectrum is dominated by the 4-line spectrum of SPRs at ,50,°C and by the 7-line spectrum of MCRs at +70,°C. At intermediate temperatures, a third spectral component is seen, which is assigned to an MCR species with restricted rotational mobility. The MCR components are produced by 1,5-hydrogen shift (backbiting) of SPRs. The measured ratio of MCRs to SPRs allows for estimating the rate coefficient k for monomer addition to a mid-chain radical. For 70,°C, k is obtained to be 65.5 L,·,mol,1,·,s,1. [source] An additional soft X-ray component in the dim low/hard state of black hole binariesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010C. Y. Chiang ABSTRACT We test the truncated disc models using multiwavelength (optical/ultraviolet/X-ray) data from the 2005 hard state outburst of the black hole Swift J1753.5,0127. This system is both fairly bright and has fairly low interstellar absorption, so gives one of the best data sets to study the weak, cool disc emission in this state. We fit these data using models of an X-ray illuminated disc to constrain the inner disc radius throughout the outburst. Close to the peak, the observed soft X-ray component is consistent with being produced by the inner disc, with its intrinsic emission enhanced in temperature and luminosity by reprocessing of hard X-ray illumination in an overlap region between the disc and corona. This disc emission provides the seed photons for Compton scattering to produce the hard X-ray spectrum, and these hard X-rays also illuminate the outer disc, producing the optical emission by reprocessing. However, the situation is very different as the outburst declines. The optical is probably cyclo-synchrotron radiation, self-generated by the flow, rather than tracing the outer disc. Similarly, limits from reprocessing make it unlikely that the soft X-rays are directly tracing the inner disc radius. Instead they appear to be from a new component. This is seen more clearly in a similarly dim low/hard state spectrum from XTE J1118+480, where the 10 times lower interstellar absorption allows a correspondingly better view of the ultraviolet/extreme ultraviolet (EUV) emission. The very small emitting area implied by the relatively high temperature soft X-ray component is completely inconsistent with the much larger, cooler, ultraviolet component which is well fit by a truncated disc. We speculate on the origin of this component, but its existence as a clearly separate spectral component from the truncated disc in XTE J1118+480 shows that it does not simply trace the inner disc radius, so cannot constrain the truncated disc models. [source] X-ray active galactic nuclei in the core of the Perseus clusterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007S. Santra ABSTRACT We present a study of the X-ray emission from the nuclei of galaxies observed in the core of the Perseus cluster in a deep exposure with Chandra. Point sources are found coincident with the nuclei of 13 early-type galaxies, as well as the central galaxy NGC 1275. This corresponds to all galaxies brighter than MB > ,18 in the Chandra field. All of these sources have a steep power-law spectral component and four have an additional thermal component. The unabsorbed power-law luminosities in the 0.5,7.0 keV band range from 8 × 1038 to 5 × 1040 erg s,1. We find no simple correlations between the K -band luminosity, or the FUV and NUV AB magnitudes of these galaxies and their X-ray properties. We have estimated the black hole masses of the nuclei using the K -band MBH,LKbol relation and again find no correlation between black hole mass and the X-ray luminosity. Bondi accretion on to the black holes in the galaxies with minihaloes should make them much more luminous than observed. [source] The nature of X-ray spectral variability in Seyfert galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003Richard D. Taylor ABSTRACT We use a model-independent technique to investigate the nature of the 2,15 keV X-ray spectral variability in four Seyfert galaxies and distinguish between spectral pivoting and the two-component model for spectral variability. Our analysis reveals conclusively that the softening of the X-ray continuum with increasing flux in MCG,6-30-15 and NGC 3516 is a result of summing two spectral components: a soft varying component (SVC) with spectral shape independent of flux and a hard constant component (HCC). In contrast, the spectral variability in NGC 4051 can be well described by simple pivoting of one component, together with an additional hard constant component. The spectral variability model for NGC 5506 is ambiguous, due to the smaller range of fluxes sampled by the data. We investigate the shape of the hard spectral component in MCG,6-30-15 and find that it appears similar to a pure reflection spectrum, but requires a large reflected fraction (R > 3). We briefly discuss physical interpretations of the different modes of spectral variability. [source] Mapping the geochemistry of the northern Rub' Al Khali using multispectral remote sensing techniquesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2001Kevin White Abstract Spatial variations in sand sea geochemistry relate to mixing of different sediment sources and to variations in weathering. Due to problems of accessibility, adequate spatial coverage cannot be achieved using field surveys alone. However, maps of geochemical composition produced from remotely sensed data can be calibrated against limited field data and the results extrapolated over large, inaccessible areas. This technique is applied to part of the Rub' Al Khali in the northern United Arab Emirates. Trend surface analysis of the results suggests that the sand sea at this location can be modelled as an east,west mixing zone of two spectral components: terrestrial reddened quartz sands and marine carbonate sands. Optical dating of these sediments suggests that dune emplacement occurred rapidly around 10 ka BP, when sea level was rising rapidly. The spatial distribution of mineralogical components suggests that this phase of dune emplacement resulted from coastal dune sands being driven inland during marine transgression, thereby becoming mixed with rubified terrestrial sands. Copyright © 2001 John Wiley & Sons, Ltd. [source] Cardiac Autonomic Control in Patients with Refractory Epilepsy before and during Vagus Nerve Stimulation Treatment: A One-Year Follow-up StudyEPILEPSIA, Issue 3 2006Eija Ronkainen Summary:,Purpose: To elucidate possible effect of vagus nerve stimulation (VNS) therapy on interictal heart rate (HR) variability in patients with refractory epilepsy before and after 1-year VNS treatment. Methods: A 24-hour electrocardiogram (ECG) was recorded at the baseline and after 12 months of VNS treatment in 14 patients with refractory epilepsy, and once in 28 healthy age- and sex-matched control subjects. Time and frequency domain measures, along with fractal and complexity measures of HR variability, were analyzed from the ECG recordings. Results: The mean value of the RR interval (p = 0.008), standard deviation of N-N intervals (SDNN) (p < 0.001), very-low frequency (VLF) (p < 0.001), low-frequency (LF) (p = 0.001), and high-frequency (HF) (p = 0.002) spectral components of HR variability, and the Poincaré components SD1 (p = 0.005) and SD2 (p < 0.001) of the patients with refractory epilepsy were significantly lower than those of the control subjects before VNS implantation. The nocturnal increase in HR variability usually seen in the normal population was absent in patients with refractory epilepsy. VNS had no significant effects on any of the HR-variability indexes despite a significant reduction in the frequency of seizures. Conclusions: HR variability was reduced, and the nocturnal increase in HR variability was not present in patients with refractory epilepsy. One-year treatment with VNS did not have a marked effect on HR variability, suggesting that impaired cardiovascular autonomic regulation is associated with the epileptic process itself rather than with recurrent seizures. [source] Changes in the Frequency Structure of a Mating Call Decrease Its Attractiveness to Females in the Cricket Frog Acris crepitans blanchardiETHOLOGY, Issue 8 2001Klaudia Witte In many species, females often prefer male signals that are more complex than in nature or beyond the range of calls naturally produced by conspecific males in spectral, temporal and amplitude features. In this study we examined both the ability of females to recognize signals outside the normal range of spectral frequency variation seen in male advertisement calls, and the influence of increasing call complexity by adding spectral components to enhance the attractiveness of a male advertisement call in the cricket frog Acris crepitans blanchardi, while keeping its amplitude constant. We used two different natural male call groups and created the following synthetic call groups: with a dominant frequency at 3500 Hz, i.e. at the normal dominant frequency with a frequency band within the sensitivity range of the inner ear basilar papilla; with a dominant frequency at 700 Hz, i.e. outside the normal range of variation and with a frequency band outside the sensitivity range of the basilar papilla but within the range of the amphibian papilla; with two dominant frequencies, one at 700 Hz and another at 3500 Hz, stimulating the basilar and amphibian papilla simultaneously. In double choice experiments we tested all combinations of the three call groups, and we tested the 3500 Hz call groups against the same natural call groups. Additionally, we tested the 700 Hz call groups against white noise to see whether these signals are meaningful in mate choice. Females preferred 3500 Hz call groups over all other call groups. The synthetic call group was as attractive to females as the same natural call group. The 700 Hz call group was not meaningful in mate choice. The combined (700 Hz + 3500 Hz) call group was significantly less attractive to females than the 3500 Hz call group. Thus, making a call more spectrally complex without increasing its overall amplitude decreases its attractiveness to cricket frog females. [source] Spatially adaptive color filter array interpolation for noiseless and noisy dataINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 3 2007Dmitriy Paliy Abstract Conventional single-chip digital cameras use color filter arrays (CFA) to sample different spectral components. Demosaicing algorithms interpolate these data to complete red, green, and blue values for each image pixel, to produce an RGB image. In this article, we propose a novel demosaicing algorithm for the Bayer CFA. For the algorithm design, we assume that, following the concept proposed in (Zhang and Wu, IEEE Trans Image Process 14 (2005), 2167,2178), the initial interpolation estimates of color channels contain two additive components: the true values of color intensities and the errors that are considered as an additive noise. A specially designed signal-adaptive filter is used to remove this so-called demosaicing noise. This filter is based on the local polynomial approximation (LPA) and the paradigm of the intersection of confidence intervals applied to select varying scales of LPA. This technique is nonlinear and spatially-adaptive with respect to the smoothness and irregularities of the image. The presented CFA interpolation (CFAI) technique takes significant advantage from assuming that the original data is noise-free. Nevertheless, in many applications, the observed data is noisy, where the noise is treated as an important intrinsic degradation of the data. We develop an adaptation of the proposed CFAI for noisy data, integrating the denoising and CFAI into a single procedure. It is assumed that the data is given according to the Bayer pattern and corrupted by signal-dependant noise common for charge-coupled device and complementary-symmetry/metal-oxide semiconductor sensors. The efficiency of the proposed approach is demonstrated by experimental results with simulated and real data. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 105,122, 2007 [source] MarqX: a new program for whole-powder-pattern fittingJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2000Y. H. Dong MarqX is a computer program for the modelling of powder diffraction data. It can be used for an unconstrained profile fitting (pattern decomposition, PD) or constrained modelling of the whole powder pattern (Pawley method, PM), for single- as well as multiple-phase samples. The program output includes: lattice parameters or peak positions (for PM and PD, respectively), width and shape of the diffraction peak (in terms of half width at half-maximum and mixing parameter of a pseudo-Voigt function), corrected for the instrumental broadening component, intensity, peak area and profile asymmetry. In addition, errors on the goniometer zero and shift in sample position with respect to the goniometric axis can also be modelled, together with distance and relative intensity of the spectral components of the X-ray beam (e.g.K,1 and K,2). Specific output files are provided for line-profile analysis, including the Williamson,Hall plot and Warren,Averbach method. [source] Detection of the OH band fine structure in liquid water by means of new treatment procedure based on the statistics of the fractional momentsLASER PHYSICS LETTERS, Issue 11 2007S.M. Pershin Abstract Three main spectral components ,3210, 3450, and 3650 cm,1 separated by deep gaps in the Raman OH band of liquid water have been detected by a new treatment procedure of experimental data. The applied treatment is based on the statistics of the fractional moments. This approach includes the consideration of the total set of the moments (the fractional and even complex ones) and the generalized mean value functions (GMV) as a specific noise "label". The possibility of the extraction and quantitative description of the fine structure of the averaging experimental spectra is demonstrated. In the frame of the novel approach the reliable separation between Raman spectra of the distilled and Milli-Q water is obtained. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Solid-state NMR studies of the molecular structure of TaxolMAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2006Yu Ho Abstract Solid-state 13C{1H} cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been utilized to extract the molecular structure information of Taxol, which is an anti-tumor therapeutic medicine extracted from the yew bark. The 13C signals have chemical shift values quite consistent with those measured in solution phase, and the overall chemical shift range is over 200 ppm. Notably, most of the 13C resonances of the taxane ring have two clearly resolved spectral components except the resonance peaks of C-15, C-16 and C-17, which are located at the central part of the taxane ring. On the basis of our NMR data, we propose that these doublets originate from two slightly different molecular conformations of the taxane ring and still the central part of the ring remains structurally similar. Furthermore, it is demonstrated that the 13C chemical shift difference deduced from the doublet splittings can serve as a direct measure of the structural difference between the two conformations, which could possibly correlate with the anti-tumor activity of Taxol. Copyright © 2006 John Wiley & Sons, Ltd. [source] Accreting millisecond pulsar SAX J1808.4,3658 during its 2002 outburst: evidence for a receding discMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009Askar Ibragimov ABSTRACT An outburst of the accreting X-ray millisecond pulsar SAX J1808.4,3658 in 2002 October,November was followed by the Rossi X-ray Timing Explorer for more than a month. A detailed analysis of this unprecedented data set is presented. For the first time, we demonstrate how the area covered by the hotspot at the neutron star surface is decreasing in the course of the outburst together with the reflection amplitude. These trends are in agreement with the natural scenario, where the disc inner edge is receding from the neutron star as the mass accretion rate drops. These findings are further supported by the variations of the pulse profiles, which clearly show the presence of the secondary maximum at the late stages of the outburst after October 29. This fact can be interpreted as the disc receding sufficiently far from the neutron star to open the view of the lower magnetic pole. In that case, the disc inner radius can be estimated. Assuming that disc is truncated at the Alfvén radius, we constrain the stellar magnetic moment to ,= (9 ± 5) × 1025 G cm3, which corresponds to the surface field of about 108 G. On the other hand, using the magnetic moment recently obtained from the observed pulsar spin-down rate we show that the disc edge has to be within factor of 2 of the Alfvén radius, putting interesting constraints on the models of the disc,magnetosphere interaction. We also demonstrate that the sharp changes in the phase of the fundamental are intimately related to the variations of the pulse profile, which we associate with the varying obscuration of the antipodal spot. Using the phase-resolved spectra, we further argue that the strong dependence of the pulse profiles on photon energy and the observed soft time lags result from the different phase dependence of the normalizations of the two spectral components, the blackbody and the Comptonized tail, being consistent with the model, where these components have significantly different angular emission patterns. The pulse profile amplitude allows us to estimate the colatitude of the hotspot centroid to be ,4°,10°. [source] The nature of X-ray spectral variability in Seyfert galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003Richard D. Taylor ABSTRACT We use a model-independent technique to investigate the nature of the 2,15 keV X-ray spectral variability in four Seyfert galaxies and distinguish between spectral pivoting and the two-component model for spectral variability. Our analysis reveals conclusively that the softening of the X-ray continuum with increasing flux in MCG,6-30-15 and NGC 3516 is a result of summing two spectral components: a soft varying component (SVC) with spectral shape independent of flux and a hard constant component (HCC). In contrast, the spectral variability in NGC 4051 can be well described by simple pivoting of one component, together with an additional hard constant component. The spectral variability model for NGC 5506 is ambiguous, due to the smaller range of fluxes sampled by the data. We investigate the shape of the hard spectral component in MCG,6-30-15 and find that it appears similar to a pure reflection spectrum, but requires a large reflected fraction (R > 3). We briefly discuss physical interpretations of the different modes of spectral variability. [source] On the accretion geometry of Cyg X-1 in the low/hard stateMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003F. Eugenio Barrio ABSTRACT We fit the broad-band RXTE PCA and HEXTE spectrum of Cyg X-1 from 3,200 keV with reflection models which calculate the vertical ionization structure of an X-ray illuminated disc. We consider two geometries corresponding to a truncated disc/inner hot flow and magnetic flares above an untruncated disc. Both models are able to fit the PCA 3,20 keV data, but with very different spectral components. In the magnetic flare models the 3,20 keV PCA spectrum contains a large amount of highly ionized reflection, while in the truncated disc models the amount of reflection is rather small. The Compton downscattering rollover in reflected emission means that the magnetic flare models predict a break in the spectrum at the high energies covered by the HEXTE bandpass which is not seen. By contrast, the weakly illuminated truncated disc models can easily fit the 3,200 keV spectra. [source] Characterization of tissue structure at varying length scales using temporal diffusion spectroscopy,NMR IN BIOMEDICINE, Issue 7 2010John C. Gore Abstract The concepts, theoretical behavior and experimental applications of temporal diffusion spectroscopy are reviewed and illustrated. Temporal diffusion spectra are obtained using oscillating-gradient waveforms in diffusion-weighted measurements, and represent the manner in which various spectral components of molecular velocity correlations vary in different geometrical structures that restrict or hinder free movements. Measurements made at different gradient frequencies reveal information on the scale of restrictions or hindrances to free diffusion, and the shape of a spectrum reveals the relative contributions of spatial restrictions at different distance scales. Such spectra differ from other so-called diffusion spectra which depict spatial frequencies and are defined at a fixed diffusion time. Experimentally, oscillating gradients at moderate frequency are more feasible for exploring restrictions at very short distances which, in tissues, correspond to structures smaller than cells. We describe the underlying concepts of temporal diffusion spectra and provide analytical expressions for the behavior of the diffusion coefficient as a function of gradient frequency in simple geometries with different dimensions. Diffusion in more complex model media that mimic tissues has been simulated using numerical methods. Experimental measurements of diffusion spectra have been obtained in suspensions of particles and cells, as well as in vivo in intact animals. An observation of particular interest is the increased contrast and heterogeneity observed in tumors using oscillating gradients at moderate frequency compared with conventional pulse gradient methods, and the potential for detecting changes in tumors early in their response to treatment. Computer simulations suggest that diffusion spectral measurements may be sensitive to intracellular structures, such as nuclear size, and that changes in tissue diffusion properties may be measured before there are changes in cell density. Copyright © 2010 John Wiley & Sons, Ltd. [source] 1H- and 31P-MR spectroscopy of primary and recurrent human brain tumors in vitro: malignancy-characteristic profiles of water soluble and lipophilic spectral componentsNMR IN BIOMEDICINE, Issue 5 2001Fritz-Georg Lehnhardt Abstract In vitro NMR spectrocopy was performed on specimen of human brain tumors. From all patients, tissue samples of primary tumors and their first recurrences were examined. 31P- and 1H-spectra were recorded from samples of meningioma, astrocytoma and glioblastoma. A double extraction procedure of the tissue samples permitted acquisition of information from the membrane fraction and from the cytosolic fraction. 31P-spectra were used to analyze the lipophilic fraction (phospholipids of the membrane) of the tissue extracts, while the 1H-spectra reflected information on the metabolic alterations of the hydrophilic, cytosolic fraction of the tissue. The tumor types showed distinctive spectral patterns in both the 31P- and the 1H-spectra. Based on the total detectable 31P signal, the level of phosphatidylcholine was about 34% lower in primary astrocytomas than in primary glioblastomas (p,=,0.0003), whereas the level of sphingomyelin was about 45% lower in primary gioblastomas than in primary astrocytomas (p,=,0.0061). A similar tendency of these phospholipids was observed when comparing primary and recurrent astrocytoma samples from the same individuals [+15% (p,=,0.0103) and ,23% (p,=,0.0314) change, respectively]. 1H-spectra of gliomas were characterized by an increase of the ratios of alanine, glycine and choline over creatine as a function of the degree of malignancy. In agreement with findings in the 31P-spectra, the 1H-spectra of recurrent astrocytomas showed metabolic profiles of increased malignancy in comparison to their primary occurrence. Since gliomas tend to increase in malignancy upon recurrence, this may reflect evolving tumor metabolism. 1H-spectra of meningiomas showed the highest ratio of alanine over creatine accompanied by a near absence of myo-inositol. Phospholipid profiles of meningiomas showed higher fractional contents of phosphatidylcholine along with lower phosphatidylserine compared to astrocytomas, while higher phosphatidylethanolamine and sphingomyelin fractional contents distinguished meningiomas from glioblastomas. The extraction method being used in this study combined with high-resolution 1H- and 31P-MRS provides a wide range of biochemical information, which enables differentiation not only between tumor types but also between primary and recurrent gliomas, reflecting an evolving tumor metabolism. Copyright © 2001 John Wiley & Sons, Ltd. [source] Ectopic Beats in Heart Rate Variability Analysis: Effects of Editing on Time and Frequency Domain MeasuresANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 1 2001Mirja A. Salo M.Sc. Background: Various methods can be used to edit biological and technical artefacts in heart rate variability (HRV), but there is relatively little information on the effects of such editing methods on HRV. Methods: The effects of editing on HRV analysis were studied using R-R interval data of 10 healthy subjects and 10 patients with a previous myocardial infarction (Ml). R-R interval tachograms of verified sinus beats were analyzed from short-term (,5 min) and long-term (,24 hours) recordings by eliminating different amounts of real R-R intervals. Three editing methods were applied to these segments: (1) interpolation of degree zero, (2) interpolation of degree one, and (3) deletion without replacement. Results: In time domain analysis of short-term data, the standard deviation of normal-to-normal intervals (SDANN) was least affected by editing, and 30%-50% of the data could be edited by all the three methods without a significant error (< 5%). In the frequency domain analysis, the method of editing resulted in remarkably different changes and errors for both the high-frequency (HF) and the low-frequency (LF) spectral components. The editing methods also yielded in different results in healthy subjects and AMI patients. In 24-hour HRV analysis, up to 50% could be edited by all methods without an error larger than 5% in the analysis of the standard deviation of normal to normal intervals (SDNN). Both interpolation methods also performed well in the editing of the long-term power spectral components for 24-hour data, but with the deletion method, only 5% of the data could be edited without a significant error. Conclusions: The amount and type of editing R-R interval data have remarkably different effects on various HRV indices. There is no universal method for editing ectopic beats that could be used in both the time-domain and the frequency-domain analysis of HRV. A.N.E. 2001;6(1):5,17 [source] Rapid monitoring of recombinant antibody production by mammalian cell cultures using fourier transform infrared spectroscopy and chemometricsBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2010Christopher A. Sellick Abstract Fourier transform infrared (FT-IR) spectroscopy combined with multivariate statistical analyses was investigated as a physicochemical tool for monitoring secreted recombinant antibody production in cultures of Chinese hamster ovary (CHO) and murine myeloma non-secreting 0 (NS0) cell lines. Medium samples were taken during culture of CHO and NS0 cells lines, which included both antibody-producing and non-producing cell lines, and analyzed by FT-IR spectroscopy. Principal components analysis (PCA) alone, and combined with discriminant function analysis (PC-DFA), were applied to normalized FT-IR spectroscopy datasets and showed a linear trend with respect to recombinant protein production. Loadings plots of the most significant spectral components showed a decrease in the C,O stretch from polysaccharides and an increase in the amide I band during culture, respectively, indicating a decrease in sugar concentration and an increase in protein concentration in the medium. Partial least squares regression (PLSR) analysis was used to predict antibody titers, and these regression models were able to predict antibody titers accurately with low error when compared to ELISA data. PLSR was also able to predict glucose and lactate amounts in the medium samples accurately. This work demonstrates that FT-IR spectroscopy has great potential as a tool for monitoring cell cultures for recombinant protein production and offers a starting point for the application of spectroscopic techniques for the on-line measurement of antibody production in industrial scale bioreactors. Biotechnol. Bioeng. 2010; 106: 432,442. © 2010 Wiley Periodicals, Inc. [source] Effects of local arteriosclerosis on carotid baroreflex sensitivity and on heart rate and arterial pressure variability in humansCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 1 2006Ola Eiken Summary The study examined whether the alterations in heart rate variability (HRV) and baroreflex sensitivity (BRS) observed in patients with coronary artery disease can also be discerned in otherwise healthy subjects with mild-to-moderate arteriosclerosis in the carotid artery bifurcation. Based on the results of carotid duplex ultrasonography, subjects were designated as either having no arteriosclerotic lesions (n = 18), unilateral (n = 19) or bilateral lesions (n = 18) in the bifurcation. Electrocardiograms were recorded and simultaneous and continuous records of arterial pressure were obtained. Resting HRV was determined by calculating the spectral power density in three frequency bands: 0,0·05 Hz [very low frequency (VLF) band], 0·05,0·15 [low frequency (LF) band] and 0·15,2 Hz (high frequency band), whereas the arterial pressure variability (APV) was determined from spectral power density of the VLF and LF bands. Carotid BRS was evaluated by measuring R-R intervals during application of pulse-synchronous graded pressures (40 to ,65 mmHg) in a neck-chamber device. Analysis of variance revealed no effect of mild-to-moderate carotid arteriosclerosis on the spectral components of HRV and APV or on BRS. It thus appears that mild-to-moderate asymptomatic carotid arteriosclerosis does not affect carotid BRS, APV or HRV at rest. [source] Effects of pharmacological adrenergic and vagal modulation on fractal heart rate dynamicsCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 5 2001Mikko P. Tulppo Breakdown of short-term fractal-like behaviour of HR indicates an increased risk for adverse cardiovascular events and mortality, but the pathophysiological background for altered fractal HR dynamics is not known. Our aim was to study the effects of pharmacological modulation of autonomic function on fractal correlation properties of heart rate (HR) variability in healthy subjects. Short-term fractal scaling exponent (,1) along with spectral components of HR variability were analysed during the following pharmacological interventions in healthy subjects: (i) noradrenaline (NE) infusion (n=22), (ii) NE infusion after phentolamine (PHE) (n=8), (iii) combined NE + adrenaline (EPI) infusion (n=12), (iv) vagal blockade with high dose of atropine (n=10), (v) and vagal activation by low dose of atropine (n=10). Then ,1 decreased progressively during the incremental doses of NE (from 0·85 ± 0·250 to 0.55 ± 0·23, P<0·0001). NE also decreased the average HR (P<0·001) and increased the high frequency spectral power (P<0·001). Vagal blockade with atropine increased the ,1 value (from 0·82 ± 0·22 to 1·24 ± 0·41, P<0·05). Combined NE + EPI infusion and vagal activation with a low dose atropine did not result in any changes in ,1, and ,-adrenergic blockade by PHE did not completely reverse the effects of NE on ,1. Increased levels of circulating NE result in reduction of short-term correlation properties of HR dynamics. The results suggest that coactivation of cardiac vagal outflow at the time of high levels of a circulating sympathetic transmitter explains the breakdown of fractal-like behaviour of human HR dynamics. [source] | ||||||||||||||||||||||