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PubMed1997

Sympathovagal balance of the heart in subjects with spinal cord injury.

This study investigated the effect of abnormal autonomic cardiovascular function on heart rate variability (HRV) in individuals classified into four groups: complete quadriplegia, incomplete quadriplegia, low paraplegia, and non-spinal cord injury (SCI) controls. Measurements were collected at baseline and during provocative maneuvers. Spectral analysis using a fast-Fourier transform algorithm revealed two spectral components of HRV, termed low frequency (LF) and high frequency (HF); the LF-to-HF ratio (estimate of sympathovagal balance) was also calculated. Each group of subjects with quadriplegia exhibited significantly lower spectral components for both baseline and composite provocative measures compared with the non-SCI controls (P < 0.05). In addition, the group with paraplegia demonstrated significantly lower HF baseline and LF composite levels than controls (P < 0.05). No differences were observed among all groups for the LF-to-HF ratio. This consistency in the LF-to-HF ratio suggests that the two autonomic divisions that regulate the cardiovascular system maintain homeostasis even when one component is severely compromised. This is supported by the additional findings of decreased parasympathetic activity in the two groups with quadriplegia and the absence of significant differences among any of the four groups at rest in either heart rate or blood pressure.

Adult↗
PubMed1984

Red-edge excitation of fluorescence and dynamic properties of proteins and membranes.

In moderately polar and viscous solvents, the emission spectra of fluorophores often shift to longer wavelengths as the excitation wavelength is increased toward the long-wavelength (red) side of the absorption. Red shifts occur because long-wavelength excitation results in photoselection of those fluorophores which are interacting most strongly with the polar solvent molecules. The observation of excitation red shifts requires that these enhanced dipole-dipole interactions are maintained in the photoselected population during the lifetime of the excited state. Consequently, the magnitude of the excitation red shifts depends upon the dynamic properties of the environment surrounding the fluorophore, as well as upon the solvent polarity and the sensitivity of the fluorophore to the polarity of the solvent. We used this phenomenon to investigate the dynamic properties of reference solvents, model membranes, and the protein apomyoglobin labeled with 6-(p-toluidinyl)-2-naphthalenesulfonic acid (TNS). The spectral shifts and lifetime data indicate that red-edge excitation results in the selective excitation of "solvent-relaxed" fluorophores. By comparison of the data obtained for TNS in solvents and bound to the macromolecules, one may estimate the relaxation rate of the environment. This comparison indicates rapid spectral relaxation of TNS bound to lipid vesicles and a somewhat slower relaxation around TNS bound to the heme site of apomyoglobin.

Apoproteins↗
PubMed1998

Influence of duration and hour of recording on spectral measurements of heart rate variability.

UNLABELLED: Frequency-domain analysis of heart rate variability provides information about influences of autonomic nervous system on the heart and can be measured on short-term or long-term electrocardiogram recording. We compared heart rate variability on 24 h electrocardiogram recording with measurements of heart rate variability over shorter periods of 1 h and 12 h in order to determine the influence of duration and hour of recording on the heart rate variability parameters in the frequency domain. Heart rate variability was analyzed in 24 subjects with normal heart, with measurement of total power (Tot P), ULF, VLF, LF, HF and LF/HF ratio. Reference measurements over 24 h were compared with measurements over 4 periods of 1 h (2 AM-3 AM, 8 AM-9 AM, 2 PM-3 PM, 8 PM-9 PM) and over 4 periods of 12 h (2 AM-2 PM, 8 AM-8 PM, 2 PM-2 AM, 8 PM-8 AM). The correlations with measurements over 24 h were lower for the measurements over 1 h than for the measurements over 12 h. ULF had the lowest mean of correlation coefficients for measurements over 1 h and 12 h, whereas the other frequency bands had high correlations with measurements over 24 h. When using Bland and Altman method, only measurements over 2 AM-2 PM and 2 PM-2 AM periods were a reliable estimation of heart rate variability over 24 h. CONCLUSION: Spectral measurements of heart rate variability over 12 h have high correlations with measurements on 24 h. ULF is the parameter the most affected by the duration of the recording. Spectral measurements over 2 AM-2 PM and 2 PM-2 AM periods are reliable appreciations of heart rate variability over 24 h.

Adult↗
PubMed1975

Photopic spectral sensitivity of the peripheral retina.

Photopic spectral sensitivity was determined in the mid- and far-peripheral retina by two methods. The first consisted of measuring increment thresholds on a background similar in spectral composition to CIE Source A. The resulting spectral-sensitivity functions displayed maxima at about 440 nm, in agreement with previous work. The second method consisted of measuring dark-adaptation curves following termination of the background. From these curves, spectral-sensitivity functions were derived for various times in the dark. The results showed that the 440 nm maximum quickly diminished. When photopic thresholds were estimated from the cone plateau of the dark-adaptation curves, the spectral-sensitivity functions peaked at about 550 nm and had much the same shape from the parafovea to the far periphery. We suggest that previous findings of maximum photopic sensitivity in the short-wave region of the spectrum resulted from chromatic adaptation induced by backgrounds (such as Source A) that were weighted towards middle and long waves.

Adult↗
PubMedDate not supplied

Can 3D structural parameters be predicted from 2D (topological) molecular descriptors?

The dihedral angle between both phenyl rings determined by photoelectron spectroscopy in a series of seven alkylbiphenyl is described by the local spectral moments of the bond matrix. This series is extended to 78 alkylbiphenyl compounds by estimating the dihedral angle from molecular mechanics force field calculations. The linear correlation obtained between this angle and the local spectral moments shown a correlation coefficient of 0.9838. This result proves that 2D (topological) descriptors can account for 3D structural parameters. A new substituent constant is calculated as the contribution of groups to the studied rotational angle by using the information encoded into the local spectral moments. This substituent constant is not linearly related to the Taft's steric constants E(S) as they have a correlation coefficient of only 0.75. These steric constants are able to account only for 71% of the variance in the studied 3D parameter. The implications for QSPR/QSAR studies of the demonstration that 2D (topological) descriptors can describe 3D structural parameters are also analyzed.

Journal Article↗
PubMed1990

Activation of Torpedo acetylcholine receptors expressed in mouse fibroblasts. Single channel current kinetics reveal distinct agonist binding affinities.

The experiments described examine single channel currents recorded through Torpedo acetylcholine receptor channels stably expressed by a mouse fibroblast cell line. Closed-duration histograms were constructed from currents elicited by 0.5-300 microM acetylcholine (ACh). The concentration dependence of closed durations is well described by a four-state linear scheme with the addition of open-channel block by ACh. Analysis of closed durations measured at low concentrations gives estimates of the rate of opening of doubly liganded receptors, beta, the rate of dissociation of ACh from doubly liganded receptors, k-2, and the rate of channel closing, alpha. The rate of ACh dissociation from singly liganded receptors, k-1, is then deduced from closed-duration histograms obtained at intermediate ACh concentrations. With k-1, k-2 and beta determined, the rates of ACh association, k+1 and k+2, are estimated from fitting closed-duration histograms obtained over a range of high ACh concentrations. A complete set of rate constants is presented for three experimental conditions: (a) Ca2(+)-free extracellular solution containing 1 mM free Mg2+ at 22 degrees C, (b) Ca2(+)-free solution at 12 degrees C, and (c) extracellular Ca2+ and Mg2+, both at 0.5 mM, at 22 degrees C. For all three conditions the dissociation constant for the first agonist binding site is approximately 100-fold lower than that for the second site. The different affinities are due primarily to different dissociation rates. Both the association and dissociation rates depend strongly on temperature. At 22 degrees C ACh associates at diffusion-limited rates, whereas at 12 degrees C association is 30- to 60-fold slower. Also slowed at 12 degrees C are beta (4-fold), k-2 (3-fold), k-1 (25-fold), and alpha (15-fold). In contrast to the activation rate constants, those for ACh-induced block decrease only twofold between 22 and 12 degrees C. Changing from a Ca2(+)-free to a Ca2(+)-containing extracellular solution does not affect k+1 and k+2, but increases beta (twofold) and decreases k-2, k-1, and alpha (all twofold). Spectral analysis of single channel currents supports the parameter estimates obtained from fitting the open- and closed-duration histograms, and improves resolution of brief channel blockages produced by ACh.

Acetylcholine↗
PubMed2006

On the statistics of ultrasonic spectral parameters.

Several factors affect the accuracy and precision of ultrasonic spectrum analysis, which is used for characterization of normal and diseased tissue in a variety of organs. For example, averaging procedures and the sequence of operations affect the accuracy and precision of spectrum analysis. Averaging procedures and logarithmic conversion (i.e., conversion to dB) introduce a constant bias that affects spectral amplitudes and the values of intercept and midband fit; the bias depends on the sequencing of the log conversion and averaging as well as the number of independent spectra or spectral parameters that are averaged. We derive expressions that permit correction of such biases. Furthermore, we show that standard deviations for slope and midband-fit estimation can be minimized by averaging spectra before dB conversion and before computing spectral parameters by linear regression. Experimental results using phantoms agree remarkably with theoretical predictions for the data window functions studied in this article, Hamming and rectangular.

Humans↗
PubMed2006

Simulations of the accuracy in retrieving stratospheric aerosol effective radius, composition, and loading from infrared spectral transmission measurements.

We examine the extent to which three physical aerosol parameters--effective radius, composition (sulfate weight percent), and total volume-can be determined from infrared transmission spectra. Using simulated transmission data over the range 800-4750 cm(-1) (12.5-2.1 microm) and errors taken from the infrared spectral measurements of the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument, we use optimal estimation to recover these aerosol parameters. Uncertainties in these are examined as a function of the size, composition, and loading of stratospheric aerosols and of the spectral range employed. Using the entire spectral range above, we retrieve all three parameters with a precision to within 3% if the size distribution form is known. Additional errors result, however, from an uncertainty in the size distribution width. These are small (only a few percent) for composition and total volume but are substantial (as much as 50%) for effective radius. Errors also increase substantially when the spectral range is reduced. The retrieved effective radius can have an error of 100% or greater for typical stratospheric aerosol sizes when the spectral range is restricted to the lower wavenumber part of the range. For good accuracy in effective radius, the spectral range must extend beyond approximately 3000 cm(-1). Composition and total volume are less sensitive to the spectral range than effective radius. These simulations were carried out with modeled data to test the potential accuracy of stratospheric sulfate aerosol retrievals from the Atmospheric Chemistry Experiment (ACE). Because of the limitations that result from the use of simulated data, we have tested our retrieval algorithm using ATMOS spectra in different filter regions and present here the aerosol parameters obtained.

Journal Article↗
PubMedDate not supplied

The role of the spectral sensitivity curve in the selection of relevant biological dosimeters for solar UV monitoring.

To estimate the risk of enhanced UV-B radiation due to stratospheric ozone depletion, phage T7 and uracil thin-layer biological dosimeters have been developed, which weight the UV irradiance according to induced DNA damage. To study the molecular basis of the biological effects observed after UV irradiation, the spectral sensitivity curves of the two dosimeters and induction of the two major DNA photoproducts, cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts ((6-4)PDs), in phage T7 have been determined for polychromatic UV sources. CPDs and (6-4)PDs are determined by lesion-specific monoclonal antibodies in an immunodotblot assay. Phage T7 and uracil biological dosimeters together with a Robertson-Berger (RB) meter have been used for monitoring environmental radiation from the polar region to the equator. The biologically effective dose (BED) established with the three different dosimeters increases according to the changes in the solar angle and ozone column, but the degree of the change differs significantly. The results can be explained based on the different spectral sensitivities of the dosimeters. A possible method for determining the trend of the increase in the biological risk due to ozone depletion is suggested.

Atmosphere↗
PubMed2006

[Study on second filtering algorithm based on tracing the interfering spectral peaks of radar non-contact life-parameter detection system].

To develop a filtering algorithm which could trace the spectral peaks of the interference and which was used to extract the breath signal with the same band interference in radar non-contact life-detecting system, second filtering algorithm was studied. Through first filtering,the probable interfering spectral peaks (ISP) could be detected by Yule-Walker spectrum estimating and could be located by calculating the coefficients of normalized cross-correlation function according to standard breath signal. Thus the breath signal could be extracted through a second filtering. By using the second filtering algorithm (SFA), the same band interfering spectral peaks with breath signal could be recognized and inhibited. So we conclude that the same band mono-ISP could be inhibited by using SFA and breath signals could be effectively extracted.

Adult↗
PubMed1999

Non-invasive assessment of human baroreflex during different body positions.

Two techniques for evaluating human baroreflex sensitivity (BRS), i.e. the sequence technique and the cross-spectral technique, were compared during the following four different body positions; 6 degrees head-down tilt (HDT), supine (Sup), 60 degrees head-up tilt (HUT) and upright (Upr). The sequence technique is based on the slope of linear regression between beat-to-beat RR intervals and systolic blood pressures. The cross-spectral technique is based on the cross-spectral analysis of RR interval and systolic blood pressure variabilities, and the estimates of BRS were computed separately for the low-frequency region (0.04-0.15 Hz) and the high-frequency region (0.15-0.5 Hz). The BRS obtained by the sequence technique had a significant correlation to that obtained by the cross-spectral technique for the low-frequency region in HDT, Sup and HUT, but not in Upr. There was a significant correlation between the BRS obtained by the sequence technique and that obtained by the cross-spectral technique for the high-frequency region in every body position. It became clear that the sequence technique is mutually related to the cross-spectral technique for the high-frequency region, but not necessarily identical to the cross-spectral technique for the low-frequency region. Moreover, a comparison was also made between the baroreceptor activating sequence and the deactivating sequence in the sequence technique during the four different body positions. Although the estimates of BRS of the activating sequence and the deactivating sequence were similar in every body position, the numbers of their sequences were progressively separated in the order of HDT, Sup, HUT and Upr. The numbers of the activating sequence and the deactivating sequence in the sequence technique were found to be separated in a sympathetically dominant condition.

Adult↗
PubMed2005

Advective velocity and energy dissipation rate in an oscillatory flow.

Characterizing the transport processes at the sediment-water interface along sloping boundaries in lakes and reservoirs is of fundamental interest in lake and reservoir water quality management. The turbulent bottom boundary layer (TBBL) along a slope, induced by the breaking of internal waves in a linearly stratified fluid, was investigated through laboratory measurements. Fast response micro-scale conductivity and temperature probes in conjunction with laser-Doppler velocimetry were used to measure the time series of salinity, temperature, and velocity along a sloping boundary. Turbulent energy spectra were computed from the velocity data using a time-dependent advective velocity and Taylor's hypothesis. The energy spectra were used to estimate the energy dissipation rate at different positions in the TBBL. The advective velocity in this near-zero mean shear flow is based on an integral time scale (T(int)). The integral time scale is related to the average frequency of the spectral energy density of the flow velocity. The energy dissipation rate estimated from the variable advective velocity with an averaging time window equal to the integral time scale (T=T(int)) was 43% higher than the energy dissipation rate estimated from a constant advective velocity. The estimated dissipation rates with T=T(int) were comparable to values obtained by curve-fitting a theoretical Batchelor spectrum for the temperature gradient spectra. This study proposes the integral time scale to be used for the oscillatory flows as (a) a time-averaging window to estimate the advective velocity and associated energy dissipation level, and (b) a normalizing parameter in the energy spectrum.

Microfluidics↗
PubMed1980

Effects of illumination level on the rat's rhythmicity of brain self-stimulation behavior.

Rhythmic patterns in the rat's brain self-stimulation behavior were analyzed across levels of illumination, including conditions of constant illumination (LL), constant darkness (DD), and light-dark cycles (LD 12:12). LD entrainment was achieved with light intensities ranging from 0.25 to 440 lux, and little or no change was found in the phase-angle difference between the dominant spectral peak and the light transitions. Under constant conditions, the circadian period (tau) increased in proportion to illumination level, with means ranging from 24.10 h (DD) to 25.90 h (LL 440 lux). tau increased linearly as a function of long I within the range of 0.25 to 30 lux, yielding a change of 0.28 h for a 10-fold increment in illumination level, a value which closely matches Aschoff's [3] preliminary estimate of delta tau/delta ILL for the rat. The circadian spectral component was influenced by several factors. (1) Re-entrainment protocol. Given a succession of LL conditions without entrainment segments in between, circadian rhythmicity was obscured at high illumination levels. (2) Duration of LL exposure. Even following an entrainment segment, long-term LL resulted in reduced power or loss of the circadian component. (3) LD vs LL. Spectral power was consistently higher under entrainment than under corresponding LL intensities, and there was a trend toward reduced power as a function of LL intensity. A wide range of ultradian spectral components was found across conditions. Under entrainment, most such components were harmonics of the circadian fundamental; under constant conditions, the frequency relationships were relatively variable.

Animals↗
PubMed1993

Protein secondary structure from Fourier transform infrared and/or circular dichroism spectra.

A multivariate linear model (Gauss-Markoff model) with noise is used to analyze the estimation of protein secondary structure from spectra of 21 reference proteins whose structures are known from X-ray studies. Fourier transform infrared (FTIR) spectra from 1700 to 1500 cm-1 and circular dichroism (CD) spectra from 178 to 260 nm have been used. The secondary structure categories of interest are alpha-helix, antiparallel beta-sheets, parallel beta-sheets, beta-turns, and "other". The secondary structures are predicted from separate spectra as well as from combined FTIR and CD spectra. The characteristic spectra belonging to the secondary structures and the prediction errors are also estimated. Attention has been paid to the criteria for the choice of rank of matrices of reference spectra, which corresponds to the number of independent pieces of spectral information. Criteria used are: magnitudes of singular values, root mean square error of model fit, relative error of estimable parameters and errors in predicted secondary structure. The ranks of the spectral matrices are found to be between three and six. The model accuracy is determined by removing each protein from the sample and comparing predicted and X-ray values of secondary structure. It is concluded that the linear model is more adequate for the protein FTIR spectra than for the CD spectra. Secondary structure predictions using the FTIR amide I band (1700-1600 cm-1) and the FTIR amide II band (1600-1500 cm-1), or a combination of the two, are of comparable accuracy. In particular, antiparallel beta-sheets and "other" are more reliably estimated from FTIR spectra. However, alpha-helix is more reliably estimated from CD spectra. Combining the spectra yields the best results of both techniques for each class.

Circular Dichroism↗
PubMed2002

Estimation of the total uncertainty of sky-radiance measurements in field experimental conditions: implications for the aerosol single-scattering albedo.

We compare the spectral sky radiance measured by three ground-based optical radiometers during the second Aerosol Characterization Experiment (ACE-2) to estimate the total uncertainty of the radiance in field experimental conditions. The propagation of this uncertainty on the column-integrated aerosol single-scattering albedo omega0 at 868 nm is investigated. The radiance measurements are affected by a systematic gain uncertainty of less than 2% in the visible spectral region and within 6% in the near-IR region. Correcting the measured radiance by a systematic uncertainty reduces the dispersion of the omega0 from 0.07 to 0.03. Besides, the total relative uncertainty of the radiance measurements in field experimental conditions is within 4% at any wavelength. The corresponding uncertainty delta omega0 is 4% for an aerosol optical thickness of 0.2.

Journal Article↗
PubMed1984

Dynamic equilibrium between the two conformational states of spin-labeled tropomyosin.

Tropomyosin was labeled with a maleimide nitroxide spin-label attached to cysteine-190 via a succinimido ring which was subsequently opened by incubation at alkaline pH. Electron spin resonance (ESR) spectra showed a temperature-dependent equilibrium, below the main unfolding transition of tropomyosin, between labels which were restricted in their motion (strongly immobilized), predominating at low temperatures, and those which were highly mobile (weakly immobilized), predominating at higher temperatures. These label states were associated with two protein states from a comparison of the ESR spectral changes with the thermal unfolding profile of tropomyosin. The strongly immobilized labels were associated with the completely folded molded and the weakly immobilized labels with a partially unfolded (in the cysteine-190 region) state which is an intermediate in the thermal unfolding of tropomyosin. A spectral subtraction technique was used to measure the concentration ratio of strongly and weakly immobilized labels from which an equilibrium constant, K, was determined at different temperatures. A linear van't Hoff plot was obtained, indicating that the spin-labeled protein is in thermal equilibrium between these two conformational states with delta H = 17 kcal/mol, delta S = 56 cal/(deg X mol), and K = 1.0 at 34 degrees C. An upper limit of 10(7) s-1 for the conformational fluctuation was estimated from the shapes and separation of the two ESR spectral components. In contrast to the label with the opened succinimido ring, the spin-label with an intact succinimido ring remained strongly immobilized on the protein, indicating that in the partially unfolded state the molecule retains structure in the cysteine-190 region.

Animals↗
PubMed1987

Spectral analysis of the EEG. Some fundamentals revisited and some open problems.

This tutorial was presented during the 1986 training course of the International Pharmaco-EEG Group (IPEG) in Santa Margherita Ligure, Italy. During recent years spectral analysis has been increasingly used in experimental EEG. However, to avoid misinterpretations of results, its limitations must still be carefully considered. The tutorial starts with revisiting the fundamentals of the technique, emphasizes the practical estimation of auto- and cross-spectra, discusses the assumptions underlying the spectral analysis of stochastic processes, and ends with a brief discussion concerning the postprocessing of spectral data.

Computers↗
PubMed1978

Some waveform and spectral features of vowel roughness.

Acoustic wave-period variation (jitter) and acoustic wave-amplitude variation (shimmer) associated with vowel phonations representing a range of vocal roughness were investigated. Twenty normal-speaking adult males phonated each of the vowels /u/, /i/, /v/, /a/, and /ae/, first normally and then with simulated abnormal vocal roughness. Twenty hoarse adult males, each presenting a medically diagnosed laryngeal pathology, also produced each of the five test vowels. To provide a measurable presentation of the frequency and amplitude variations of interest, each recorded vowel was band-pass filtered to isolate the fundamental frequency component. Relations of the jitter and shimmer indices (obtained from the filtered vowel waves) to acoustic spectral noise levels and to roughness ratings for the vowel phonations were studied. The findings supported the hypothesis that increases in vowel acoustic wave variability (estimated by period or amplitude variation or both) are associated with increases in vowel spectral noise levels and perceived vowel roughness. The findings also suggested, for most of the vowels studied, that cyclic peak amplitude variation may provide a better index of perceived roughness than cyclic period variation. Vowel spectral noise levels, however, may provide a more clinically useful indicant of vowel roughness than the waveform variability indices derived from the filtering procedure employed in this study.

Acoustics↗