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PubMed2000

Near-ultraviolet magnetic circular dichroism spectroscopy of protein conformational states: correlation of tryptophan band position and intensity with hemoglobin allostery.

The near-UV magnetic circular dichroism spectroscopy of the aromatic amino acid bands of hemoglobin was investigated as a potential probe of structural changes at the alpha(1)beta(2) interface during the allosteric transition. Allosteric effectors were used to direct carp and chemically modified human hemoglobins into the R (relaxed) or T (tense) state in order to determine the heme-ligation-independent spectral characteristics of the quaternary states. The tryptophan magnetic circular dichroism (MCD) peak observed at 293 nm in the R state of N-ethylsuccinimide- (NES-) des-Arg-modified human hemoglobin (Hb) was shifted to a slightly longer wavelength in the T state, consistent with the shift expected for tryptophan acting as a proton donor in a T-state hydrogen bond. Moreover, the increase observed in the T-state MCD intensity of this band relative to the R-state intensity was consistent with the effect expected for proton donation by tryptophan on the basis of the Michl perimeter model of aromatic MCD. The peak-to-trough magnitude of the R - T MCD difference spectrum is equal to 30% of the total R-state peak intensity contributed by all six tryptophans present in the human tetramer; the relative magnitude specific to the two beta37 tryptophans undergoing conformational change is estimated accordingly to be 3 times larger. The Trp-beta37 spectral shift, about 200 cm(-)(1), is in good agreement with the shifts observed in other H-bonded proton donors and provides corroborating spectral evidence for the formation in solution of a T-state Trp beta37-Asp alpha94 hydrogen bond observed in X-ray diffraction studies of deoxyHb crystals.

Allosteric Regulation↗
PubMed2002

NREM sleep EEG frequency spectral correlates of sleep complaints in primary insomnia subtypes.

STUDY OBJECTIVES: To determine whether the frequency spectrum of the sleep EEG is a physiologic correlate of 1) the degree to which individuals with persistent primary insomnia (PPI) underestimate their sleep time compared with the traditionally scored polysomnogram (PSG) and 2) the sleep complaints in PPI subjects who have relatively long traditionally scored PSG sleep times and relatively greater underestimation of sleep time. DESIGN: We compared EEG frequency spectra from REM and NREM sleep in PPI subjects subtyped as subjective insomnia sufferers (those with relatively long total sleep time and relative underestimation of sleep time compared with PSG), and objective insomnia sufferers (those with relatively short PSG total sleep time) with EEG frequency spectra in normals. We also studied the correlation between these indices and the degree of underestimation of sleep. Further, we determined the degree to which sleep EEG indexes related to sleep complaints. SETTING: Duke University Medical Center Sleep Laboratory. PARTICIPANTS: Normal (N=20), subjective insomnia (N=12), and objective insomnia (N=18) subjects. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Lower delta and greater alpha, sigma, and beta NREM EEG activity were found in the patients with subjective insomnia but not those with objective insomnia, compared with the normal subjects. These results were robust to changes in the subtyping criteria. No effects were found for REM spectral indexes. Less delta non- REM EEG activity predicted greater deviation between subjective and PSG estimates of sleep time across all subjects. For the subjective insomnia subjects, diminished low-frequency and elevated higher frequency non- REM EEG activity was associated with their sleep complaints. CONCLUSIONS: NREM EEG frequency spectral indexes appear to be physiologic correlates of sleep complaints in patients with subjective insomnia and may reflect heightened arousal during sleep.

Adult↗
PubMed1982

Spectral evidence for three metal-linked ionization equilibria in the interaction of cobalt(II) horse liver alcohol dehydrogenase with coenzyme and substrate.

The visible absorption bands in the region 525-575 nm of the catalytic cobalt ion in cobalt(II) horse liver alcohol dehydrogenase show characteristic pH-dependent changes both in the free enzyme and its complexes with nicotinamide adenine dinucleotide (NAD+) and NAD+ plus ethanol or 2,2,2-trifluoroethanol. In the free enzyme, the change of the coordination environment has an apparent pK of about 9.4. In the binary complex with NAD+ the spectral changes are complex, indicating changes in the coordination sphere in a lower pH range with an estimated pK value of about 7.9. The ternary complexes enzyme X NAD+ X ethanol and enzyme X NAD+ X 2,2,2-trifluoroethanol exhibit very similar, characteristic spectral features; their apparent pK values are 6.3 and less than 4, respectively. We ascribe these pK values to the ionization of the alcohol bound in the ternary complexes. The results demonstrate that the catalytic cobalt ion is sensing changes of the ionization state of the protein when going from low pH forms to high pH forms both in the absence and presence of coenzyme and substrate/inhibitor.

Alcohol Dehydrogenase↗
PubMed1990

The influence of spectral prominence on perceived vowel quality.

Research indicates that, when the first and second formants of a vowel are separated by less than about 3.5 Bark, perception of its height and some other aspects of its quality is determined by some weighted average of the low-frequency spectrum, rather than by particular harmonic or hypothetical formant frequencies (as is the case with more widely spaced formants). This spectral averaging has been called the center of gravity (COG) effect. Although the existence of the effect is generally accepted, the factors that govern it are poorly understood. One possibility is that the influence of the spectral envelope on perceived vowel quality increases as low-frequency spectral prominences become less well defined. A series of three experiments examined this possibility in: (1) nasal vowels, where the lowest spectral prominence is broader and flatter than that of oral vowels; (2) one- versus two-formant vowels with bandwidths appropriate for oral vowels; and (3) two-formant vowels with very narrow or very wide bandwidths. The results of these experiments show that, when two or more spectral peaks lie within 3.5 Bark of one another, F1 and the centroid (an amplitude-weighted average frequency that estimates the COG in the low-frequency spectrum) roughly determine the boundaries within which the perceptual COG lies; the frequencies of spectral peaks dominate responses when formant bandwidths are narrow, whereas overall spectral shape exerts more influence when spectral prominences are wide. Assuming that all vowels undergo the same processing, it is suggested that vowel quality, particularly height, is determined both by the frequency of the most prominent harmonics in the low-frequency region and by the slopes of the skirts in the vicinity of these harmonics. These two effects are most clearly separable in vowels with poorly defined spectral prominences whose shape cannot be adequately described by specifying the frequencies and degree of prominence of just one or two harmonics, or hypothetical formant peaks.

Adolescent↗
PubMed1993

Usefulness of difference spectroscopy in the study of the binding of uracil derivatives to human serum albumin.

Propylthiouracil is an antithyroid drug which is carried by the blood, thanks to its binding with human seroalbumin (HSA), and induces a structural alteration in HSA that changes the binding capability of other ligands. Then, with the aim of fixing the functional group in propylthiouracil involved in the interactions with HSA, the binding parameters for several uracil derivatives bound on HSA have been estimated. Interaction of propyluracil, thiouracil and propylthiouracil with HSA leads to the formation of complexes that show spectral shifts. These spectral shifts are a measure of the fraction of chromophoric groups, which is perturbed in the interaction with HSA, and thus can be used in the ligand binding estimate. The difference spectroscopy results correspond to the binding on a single centre in HSA. The difference spectra of propyluracils in seroalbumin coincide with those of propyluracils in a perturbant solvent (ethanol). On the other hand, propylthiouracil and propyluracil bind to seroalbumin on a larger scale than uracil and thiouracil. Thus, we can conclude that this binding is strengthened by hydrophobic interactions between the propyl group in propyluracils and apolar substituents on HSA.

Humans↗
PubMed1985

The rhythmic structure of mother-infant interaction in term and preterm infants.

The purpose of this study was to quantify social interaction rhythms in 3- and 5-month-old term and preterm infants and their mothers. Infant-mother dyads were videotaped in a 3-min face-to-face paradigm. For each second of the interaction, separate scores were assigned to infant and mother indicating levels of affective involvement, creating 2 180-sec time series. Spectral and cross-spectral techniques were used to quantify periodicities in each member of the dyad and to estimate the synchrony or coherence of interactional rhythms between each infant and mother. Results showed the existence of periodicities in the behavior of each infant and mother at 3 and 5 months, with most subjects showing spectral peaks between .022 and .10 Hz. Increases from 3 to 5 months in behavioral periodicities were found for infants and mothers as well as for the coherence between infant-mother dyads. Term dyads showed higher coherence than preterm dyads at both 3 and 5 months. Term infants more often led the interaction at both ages. These results were taken as evidence that behavioral periodicities, which may be biologically based, underlie early mother-infant interaction and provide a temporal structure for the organization of cognitive and affective experience. Differences in synchrony between term and preterm infants may explain later reported differences in language between these groups.

Age Factors↗
PubMed2006

[Hyperspectral remote sensing estimation models on vegetation coverage of natural grassland].

By using ASD FieldSpec Pro FR spectroradiometer, the spectral measurement of natural grassland in Xilingole Leaguer of Inner Mongolia was performed, with the vegetation coverage of natural grassland calculated, and the correlation of 25 hyperspectral feature variables with the vegetation coverage of natural grassland was analyzed. The results showed that there were 17 variables correlated significantly with the vegetation coverage of natural grassland, among which, the correlation coefficient between vegetation coverage and the area of red edge peak calculated as the sum of the amplitudes between 680 nm and 780 nm (sigma dr 680 - 780 nm) was the highest, with the value of 0.781. The basic experimental data including the vegetation coverage and canopy reflectance of natural grassland were classified into two groups. One group was used as the training sample to build the regression models with one-sample linear method, nonlinear method, and stepwise analysis method, while the other was used as the testing sample to test the precision of regression models. It was suggested that the variable of the area of red edge peak calculated as the sum of amplitudes between 680 nm and 780 nm (sigma dr 680 - 780 nm) was the best one to univariate general linear model, with a standard deviation of 10.4% and an estimation precision of 83.99%, while the stepwise regression technique was not effective to estimate the grassland coverage with raw hyperspectral canopy reflectance.

Conservation of Natural Resources↗
PubMed2003

Optimization of attenuation estimation in reflection for in vivo human dermis characterization at 20 MHz.

In vivo skin attenuation estimators must be applicable to backscattered radio frequency signals obtained in a pulse-echo configuration. This work compares three such estimators: short-time Fourier multinarrowband (MNB), short-time Fourier centroid shift (FC), and autoregressive centroid shift (ARC). All provide estimations of the attenuation slope (beta, dB x cm(-1) x MHz(-1)); MNB also provides an independent estimation of the mean attenuation level (IA, dB x cm(-1)). Practical approaches are proposed for data windowing, spectral variance characterization, and bandwidth selection. Then, based on simulated data, FC and ARC were selected as the best (compromise between bias and variance) attenuation slope estimators. The FC, ARC, and MNB were applied to in vivo human skin data acquired at 20 MHz to estimate betaFC, betaARC, and IA(MNB), respectively (without diffraction correction, between 11 and 27 MHz). Lateral heterogeneity had less effect and day-to-day reproducibility was smaller for IA than for beta. The IA and betaARC were dependent on pressure applied to skin during acquisition and IA on room and skin-surface temperatures. Negative values of IA imply that IA and beta may be influenced not only by skin's attenuation but also by structural heterogeneity across dermal depth. Even so, IA was correlated to subject age and IA, betaFC, and betaARC were dependent on subject gender. Thus, in vivo attenuation measurements reveal interesting variations with subject age and gender and thus appeared promising to detect skin structure modifications.

Adult↗
PubMed1993

Twenty-four-hour power spectral analysis by maximum entropy method of blood pressure in primary hyperaldosteronism.

In the present study we estimated the periodic profiles and variance structure of systolic blood pressure, diastolic blood pressure, heart rate and mean arterial pressure by using an autoregressive model of power spectrum, Maximum Entropy Method (MEM) in 8 patients with primary aldosteronism, during long-term therapy with nicardipine slow release. The four blood pressure variables were measured at 30-min intervals, using a noninvasive device (Spacelabs 90202) in 8 hypertensive patients of whom 6 with idiopathic aldosteronism (IHA) and 2 with dexamethasone-suppressible aldosteronism (DSH), before and after 24 weeks of 80 mg nicardipine daily. Blood pressure data were processed by MEM and spectral profiles were obtained. During nicardipine therapy all patients showed a significant decrease of 24-h ambulatory blood pressure values (p < 0.01). Before therapy, spectrum analysis by MEM indicated the presence of high frequency distribution of peaks for SBP, DBP, MAP and HR. The MEM power spectrum showed an increase in amplitude of sharp peaks of systolic, diastolic, MAP and heart rate in all patients after therapy at 24 h corresponding to the circadian rhythm blood pressure. Furthermore, the trend of these variables synchronized themselves in the same period after 24 weeks of nicardipine therapy, with spectral patterns of blood pressure similar to those of normotensive subjects. This chronobiologic approach, by Maximum Entropy Method, may be used as an alternative statistical analysis to search for possible rhythmic behavior of ambulatory blood pressure data before and after pharmacological treatment in secondary hypertensive patients.

Activity Cycles↗
PubMed2006

[Nitrogen stress measurement of canola based on multi-spectral charged coupled device imaging sensor].

Site-specific variable nitrogen application is one of the major precision crop production management operations. Obtaining sufficient crop nitrogen stress information is essential for achieving effective site-specific nitrogen applications. The present paper describes the development of a multi-spectral nitrogen deficiency sensor, which uses three channels (green, red, near-infrared) of crop images to determine the nitrogen level of canola. This sensor assesses the nitrogen stress by means of estimated SPAD value of the canola based on canola canopy reflectance sensed using three channels (green, red, near-infrared) of the multi-spectral camera. The core of this investigation is the calibration methods between the multi-spectral references and the nitrogen levels in crops measured using a SPAD 502 chlorophyll meter. Based on the results obtained from this study, it can be concluded that a multi-spectral CCD camera can provide sufficient information to perform reasonable SPAD values estimation during field operations.

Agriculture↗
PubMed2002

Reconstruction of ultrasonic fields by deconvolving the hydrophone aperture effects. I. Theory and simulation.

In many ultrasound applications-especially in the area of medical diagnostics-conventional sensors and particularly piezoelectric hydrophones do not comply with the requirements for "point detectors". It therefore suggests itself to develop methods, which allow ultrasonic fields to be reconstructed from the spatially averaged measurement values with the necessary spatial resolution. In this publication, this task will be treated as an inverse problem. It will be shown by simulations that it is possible with the aid of reconstruction methods to invert the aperture effects of the sensor. Three different reconstruction methods are tested: (1) Wiener's method furnishes the best approximation of the field to be reconstructed in the sense of the minimum mean square error. (2) The power spectral equalization method is based on equalization between the spatial power spectral densities of the field to be reconstructed and that of its estimated value. (3) With the maximum a-posteriori method, the maximum a-posteriori probability density function for the reconstructed field is searched. The results of this paper show that the quality of reconstruction depends on the signal-to-noise ratio (SNR) and the spatial frequency bandwidth of the sound field investigated. Good quality reconstructions were obtained at correlation coefficients larger than 0.995 and an SNR of at least 40 dB. In general, the quality of reconstruction decreases with decreasing SNR and is unacceptable at SNR = 20 dB. The quality also decreases with decreasing axial distance from the source that is with increasing spectral frequency bandwidth.

Journal Article↗
PubMed1994

Quantal analysis based on spectral methods.

A method for calculating quantal size based on spectral analysis of postsynaptic potential (PSP) amplitude distributions was developed and tested by Monte-Carlo techniques. It was combined with a test to reveal the bias of the estimate of quantal size and to determine whether the peaks in amplitude distributions reflect quantal release or a sampling artifact. Spectral density was computed using fast Fourier transformation after subtraction of a fitted polynomial from the probability density function. The method overestimated quantal size for values less than two standard deviations of noise, indicating that those estimates as well as estimates of quantal size computed for examples of non-quantal distributions are not reliable. This was the case for 34 of 36 sets of sensorimotor excitatory PSPs of the frog, suggesting that most values of the quanta in synapses between primary fibres and lumbar motoneurons are smaller than 70-90 microV.

Animals↗
PubMed1985

[Continuous monitoring of cerebral blood volume in cats using a reflectance spectrophotometer].

The importance of cerebral blood volume (CBV) as a physiological parameter has been well recognized, especially in its relation to the intracranial pressure (ICP). Although various methods have been applied to measure CBV, several problems and difficulties still remain to be settled. In the present study, noninvasive monitoring of CBV on the cortical surface was done with organ reflectance spectrophotometry. Through the cranial window, the cat brain was illuminated by the white light via optical fibers and reflected light was analized by spectrophotometer equipped with microcomputer and image-sensor (Sumitomo Elec. Co., Spectrum analyzer TS-200), which enables to estimate CBV on real time as the absorbance value at the isobestic point of the spectral curve of hemoglobin (Hb). In order to ascertain the reliability and reproducibility, the change of CBV was examined by 5% & 10% CO2 inhalation, 5% O2 inhalation and bilateral jugular vein occlusion. A linear correlation was found between PaCO2 and Hb absorbance value on CO2 inhalation. By the bilateral jugular vein occlusion, Hb increased concomitantly with ICP, while cerebral blood flow (CBF) decreased. On 5% O2 inhalation, absorbance spectral pattern of tissue Hb changed from that of oxy-Hb to deoxy-Hb without change of absorbance value at the isobestic point. Thus, the Hb absorbance value obtained by this spectrophotometer was considered to be reliable for the estimation of CBV on the cortical surface. Using this, the change of CBV was examined on the drug-induced seizure and post-decompression state after sustained intracranial hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Assessing carotenoid content in plant leaves with reflectance spectroscopy.

Spectral reflectance of maple, chestnut and beech leaves in a wide range of pigment content and composition was investigated to devise a nondestructive technique for total carotenoid (Car) content estimation in higher plant leaves. Reciprocal reflectance in the range 510 to 550 nm was found to be closely related to the total pigment content in leaves. The sensitivity of reciprocal reflectance to Car content was maximal in a spectral range around 510 nm; however, chlorophylls (Chl) also affect reflectance in this spectral range. To remove the Chl effect on the reciprocal reflectance at 510 nm, a reciprocal reflectance at either 550 or 700 nm was used, which was linearly proportional to the Chl content. Indices for nondestructive estimation of Car content in leaves were devised and validated. Reflectances in three spectral bands, 510+/-5 nm, either 550+/-15 nm or 700+/-7.5 nm and the near infrared range above 750 nm are sufficient to estimate total Car content in plant leaves nondestructively with a root mean square error of less than 1.75 nmol/cm2.

Algorithms↗
PubMed2005

Selective homonuclear Hartmann-Hahn transfer method for in vivo spectral editing in the human brain.

A novel selective homonuclear Hartmann-Hahn transfer method for in vivo spectral editing is proposed and applied to measurements of gamma-aminobutyric acid (GABA) in the human brain at 3 T. The proposed method utilizes a new concept for in vivo spectral editing, the spectral selectivity of which is not based on a conventional editing pulse but based on the stringent requirement of the doubly selective Hartmann-Hahn match. The sensitivity and spectral selectivity of GABA detection achieved by this doubly selective Hartmann-Hahn match scheme was superior to that achievable by conventional in vivo spectral editing techniques providing both sensitivity enhancement and excellent suppression of overlapping resonances in a single shot. Since double-quantum filtering gradients were not employed, singlets such as the NAA methyl group at 2.02 ppm and the creatine methylene group at 3.92 ppm were detected simultaneously. These singlets may serve as navigators for the spectral phase of GABA and for frequency shifts during measurements. The estimated concentration of GABA in the frontoparietal region of the human brain in vivo was 0.7 +/- 0.2 mumol/g (mean +/- SD, n = 12).

Brain Chemistry↗
PubMed2001

On multivariate spectral analysis of fMRI time series.

Most of functional magnetic resonance imaging (fMRI) time series analysis is based on single voxel data evaluation using parametric statistical tests. The result of such an analysis is a statistical parametric map. Voxels with a high significance value in the parametric test are interpreted as activation regions stimulated by the experimental task. However, for the investigation of functional connectivities it would be interesting to get some detailed information about the temporal dynamics of the blood oxygen level-dependent (BOLD) signal. For investigating that behavior, a method for fMRI data analysis has been developed that is based on Wiener theory of spectral analysis for multivariate time series. Spectral parameters such as coherence measure and phase lead can be estimated. The resulting maps give detailed information on brain regions that belong to a network structure and also show the temporal behavior of the BOLD response function. This paper describes the method and presents a visual fMRI experiment as an example to demonstrate the results.

Adult↗
PubMed1990

The influence of exercise intensity on the power spectrum of heart rate variability.

The power spectral analysis of R-R interval variability (RRV) has been estimated by means of an autoregressive method in seven sedentary males at rest, during steady-state cycle exercise at 21 percent maximal oxygen uptake (%VO2max), SEM 2%, 49% VO2max, SEM 2% and 70% VO2max, SEM 2% and during recovery. The RRV, i.e. the absolute power of the spectrum, decreased 10, 100 and 500 times in the three exercise intensities, returning to resting value during recovery. In the RRV power spectrum three components have been identified: (1) high frequency peak (HF), central frequency about 0.24 Hz at rest and recovery, and 0.28 Hz, SEM 0.02, 0.37 Hz, SEM 0.03 and 0.48 Hz, SEM 0.06 during the three exercise intensities, respectively; (2) low frequency peak (LF), central frequency about 0.1 Hz independent of the metabolic state; (3) very low frequency component (VLF), less than 0.05 Hz, no peak observed. The HF peak power, as a percentage of the total power (HF%), averaged 16%, SEM 5% at rest and did not change during exercise, whereas during recovery it decreased to 5%-10%. The LF% and VLF% were about 50% and 35% at rest and during low exercise intensity, respectively. At higher intensities, LF% decreased to 16% and VLF% increased to 70%. During recovery a return to resting values occurred. The HF component may reflect the increased respiratory rate and the LF peak changes the resetting of the baroreceptor reflex with exercise. The hypothesis is made that VLF fluctuations in heart rate might be partially mediated by the sympathetic system.

Adult↗
PubMed1985

Variations of rhythmic diameter changes at the arterial microvascular bifurcations.

The variation of the pattern of the rhythmic diameter changes, in the hamster skin fold window preparation, was studied sequentially along the branching network of the arterial vessels, from A1 small arteries (70-100 micron diameter) to A4 terminal arterioles (less than 15 micron diameter). Contraction and dilation waveforms were characterized at all subsequent levels of bifurcation. The frequency of vasomotion was determined by a specialized spectral method called PRONY, which approximates the spectral composition of complex waveforms by the least square criteria and estimates the coefficient of correlation between reconstructed and original data. It was found that the frequency of vasomotion changes abruptly at the branching points, systematically increasing in the downstream direction. The power spectrum showed that the frequencies, which appear to originate at the bifurcations and have maximum amplitude at these points, are also found in the upstream waveforms. The downstream propagation of contractions and dilations causes superposition of waves. Thus the pattern of vasomotion is the composite effect of signals that originate at various branching points and spread downstream and upstream in the microvasculature. It seems likely to suggest that single unit smooth muscle cells, located at the branchings (local pacemakers), control the arterial rhythmic diameter changes. This time dependent phenomenon affects deeply the microvascular blood flow.

Animals↗