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PubMed1994

Spectral components of short-term RR interval variability in healthy subjects and effects of risk factors.

Cardiac neural control can be estimated by frequency domain characterization of RR interval variations. This technique may become a clinical tool, as autonomic dysfunction is involved in the pathophysiology of sudden cardiac death. The study was designed to investigate 24-h cardiac autonomic control in 104 healthy subjects aged 40-77 years and to evaluate the impact of gender, age, smoking and physical training level. The sympathovagal balance was evaluated by spectral analysis of RR interval oscillations. The square-root of power of the high- (HF; 0.15-0.40) and low-frequency (LF; 0.04-0.15 Hz) bands were considered indexes of the vagal function and of the sympathovagal interaction, respectively. In addition, the precise centre frequency of the LF and HF oscillations was determined. The vagal mediated respiratory-dependent HF oscillation exhibited a clear circadian variation, and obtained the highest power values during sleep. The centre frequency was significantly lower during sleep (0.26 Hz vs 0.28 Hz), probably due to a slower respiratory frequency at night. Values for vagal tone were higher in physically trained subjects throughout the 24-h, and decreased by 13% for every 10-year increase in age; it was also reduced in smokers. The amplitude of the LF oscillation exhibited no clear diurnal variation. The mean LF/HF ratio was 3.1. LF power was much higher in males, was reduced by 15% per 10 year increase in age, and was lower in sedentary and smoking subjects, throughout the 24-h. The mean centre frequency of this component was reduced with advancing age (0.08 to 0.06 Hz from age 40 to 80 years). LF and HF power correlated positively, (r = 0.68), and 46% and 16% of the interindividual variation in LF and HF power, respectively, was explained by the four factors (gender, age, smoking, physical activity). Thus gender, age smoking and physical training level have a significant impact on the power and centre frequency of the HF and LF components. These effects must be addressed in investigations on autonomic balance.

Adult↗

PubMed2002

[Selection of optimum periods for rice estimation using remote sensing data based on GIS].

The optimum temporal for rice estimation using remote sensing data included the optimum temporal for rice planting area estimation and the optimum temporal for rice yield estimation. Based on GIS, the rice potential planting area was extracted. Therefore, the study area became smaller and the plant species considered decreased. So the optimum temporal for rice planting area estimation were determined through comparing the crop phonological calendars. In order to select the optimum temporal for rice yield estimation using remote sensing data, the relationships between the rice yield and agronomic parameters, the agronomic parameters and spectral variables, the rice yield and spectral variables for different development stages using field experiment data in 1989 and 1990 were studied. The result showed that the key period of rice production was from boot stage to heading stage. At last, the optimum temporal for rice yield estimation using remote sensing data was selected using the rice phenological calendars of 1998.

China↗

PubMed2002

On the importance of spectral responsivity of Robertson-Berger-type ultraviolet radiometers for long-term observations.

A system to determine the spectral responsivity of ultraviolet (UV) radiometers has been developed and is routinely operated at the Central Ultraviolet Calibration Facility, at the National Oceanic and Atmospheric Administration. The instrument and the measurement methodologies are described. Results of measurements from thermally controlled broadband UV radiometers of the Robertson-Berger (R-B)-type are described. Systematic differences in the spectral response curves for these instruments have been detected. The effect of these differences on the field operation of UV-B radiometers has been studied by calculating the instrumental response from modeled UV spectra. The differences of the weighted spectral UV irradiances, measured by two radiometers with different spectral response functions, caused by the daily variation in the position of the sun were estimated for fixed values of total ozone, altitude and albedo, and for cloud-free conditions. These differences increase with the solar zenith angle and are as large as 8%. Larger differences in the instrumental response may be produced by ozone variations. Thus, care must be taken when analyzing data from R-B radiometers and comparing results from different instruments. Routine cycling of UV-B radiometers in operative networks without a careful determination of the spectral responsivity, or small drifts of the spectral responsivity, may strongly affect the accuracy of UV radiation measurements and produce an erroneous trend. Because of the possible differences among radiometers, it would not be practical to derive the long-term behavior of UV radiation without routine and thorough characterization of the spectral responsivities of the instruments.

Journal Article↗

PubMed2003

Remote sensing of sediment characteristics by optimized echo-envelope matching.

A sediment geoacoustic parameter estimation technique is described which compares bottom returns, measured by a calibrated monostatic sonar oriented within 15 degrees of vertical and having a 10 degree-21 degree beamwidth, with an echo envelope model based on high-frequency (10-100 kHz) incoherent backscatter theory and sediment properties such as: mean grain size, strength, and exponent of the power law characterizing the interface roughness energy density spectrum, and volume scattering coefficient. An average echo envelope matching procedure iterates on the reflection coefficient to match the peak echo amplitude and separate coarse from fine-grain sediments, followed by a global optimization using a combination of simulated annealing and downhill simplex searches over mean grain size, interface roughness spectral strength, and sediment volume scattering coefficient. Error analyses using Monte Carlo simulations validate this optimization procedure. Moderate frequencies (33 kHz) and orientations normal with the interface are best suited for this application. Distinction between sands and fine-grain sediments is demonstrated based on acoustic estimation of mean grain size alone. The creation of feature vectors from estimates of mean grain size and interface roughness spectral strength shows promise for intraclass separation of silt and clay. The correlation between estimated parameters is consistent with what is observed in situ.

Models, Theoretical↗

PubMed2005

Comparison of different methods to identify and quantify balance control.

The goal of this paper is to clarify the methodological aspects of studies of human balance during quiet standing and perturbed standing. Centre of mass (CoM), centre of pressure (CoP) and electromyogram (EMG) or similar measures are commonly recorded to quantify human balance control. In this paper we show that to identify the rigid body dynamics and the physiological mechanism that controls the body separately, one has to externally perturb the body with known perturbations and to use the indirect (IA) or joint input-output approach (JA) for identification. However, in many balance control studies the direct approach (DA) have been used, which is well suited to study open-loop systems but will give erroneous results when applied to a closed-loop system, as in human balance control. The cross-correlation function and linear regression are examples of the erroneous application of the DA approach in human balance control studies. The consequences of this erroneous DA are given. In addition a new application of the JA is presented that identifies physiological mechanisms that control balance, including passive and active feedback pathways. This new method is compared with existing identification schemes that use the IA and an existing JA that estimates the active pathway. Also it is shown how descriptive measures such as the power spectral densities (PSD) or the stabilogram diffusion plot (SDP) of the CoP and/or CoM depends on the PSD of internal perturbations and sensor noise, which are not measured. Although descriptive measures can be used to describe the state of the balance control system for a particular situation, it does not separate the dynamics of unknown processes that perturb balance from the dynamics of the active and passive feedback mechanisms that controls balance. Only the IA and the preferred JA can give estimates of the passive and active passive feedback mechanisms that control balance.

Algorithms↗

PubMed2007

Improved transverse flow estimation using differential maximum Doppler frequency.

Conventional Doppler technique can only provide the axial component of the blood flow vector, which is actually a three dimensional (3-D) quantity. To acquire the complete flow vector, estimations of the other two velocity components are essential. For the two dimensional (2-D) Doppler-bandwidth-based transverse estimation, however, accuracy is generally limited because of the complex dependence of the Doppler spectral shape on the flow variation within the sample volume. Two factors that may lead to the Doppler spectral change were considered in this study. One is the position offset of the sample volume and the other is the length of the sample volume. Simulations were performed and experimental data were also collected. Results indicate that the position offset may result in severe underestimation of Doppler shift frequency. Consequently, Doppler bandwidth is overestimated when it is determined by the difference between Doppler shift frequency and maximum Doppler frequency. Compared with the position offset, influence of the length of sample volume on the Doppler bandwidth is minor. To overcome this problem, a novel method, which is based on the differential maximum Doppler frequency, is proposed. Specifically, two beams with different beam widths are simultaneously generated to observe the blood flow and the difference between the corresponding maximum Doppler frequencies is used to estimate the transverse velocity. It is demonstrated that the accuracy and stability of transverse estimation are significantly improved by the proposed method even when the position offset is present.

Blood Flow Velocity↗

PubMed1998

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

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

Animals↗

PubMed1997

Hemodynamic imaging with pulsatility-index and resistive-index color Doppler US.

Pulsatility index and resistive index were mapped with color Doppler ultrasound (US) and compared with spectral Doppler US findings. In the carotid arteries and/or kidneys in 12 healthy subjects, the pulsatility index and resistive index were estimated from mean frequency shifts and mapped into "cool-warm" or "rainbow" color scales. Surveys that depicted intervessel variations in a complex vascular field were useful in deciding where to perform spectral Doppler US. Intravessel variations were consistent with fluid dynamic theory.

Adolescent↗

PubMed2001

Ropivacaine in the horse: its pharmacological responses, urinary detection and mass spectral confirmation.

This report evaluates the pharmacological responses, urinary detection and mass spectral confirmation of ropivacaine in horses. Ropivacaine, a potent local anesthetic (LA) recently introduced in human medicine, has an estimated highest no-effect dose (HNED) of about 0.4 mg/site as determined in our abaxial sesamoid block model. Apparent ropivacaine equivalents were detectable by ELISA screening using a mepivacaine ELISA test after administration of clinically effective doses. Mass spectral examination of postadministration urine samples showed no detectable parent ropivacaine, but a compound indistinguishable from authentic 3-hydroxyropivacaine was recovered from these samples. The study shows that ropivacaine is a potent LA in the horse, that clinically effective doses can be detected in postadministration samples by ELISA-based screening, and that its major post administration urinary metabolite is 3-hydroxyropivacaine.

Amides↗

PubMed2006

A dynamic method to estimate the time split between the A2 and P2 components of the S2 heart sound.

The time interval between the aortic (A2) and the pulmonary (P2) components of the second heart sound (S2) is an indicator of pulmonary arterial pressure. However, knowledge of the A2 and P2 components of the S2 sound is difficult to obtain due to their temporal overlap and significant spectral similarity. In this work, we aim to extract the A2 and P2 components from the phonocardiogram to estimate the time interval between them. We attain our objective by first isolating the S2 sound from the phonocardiogram by utilizing the mode complexity of the heart. Then, we assume the statistical independence of the A2 and P2 components and extract them from the S2 sound by the application of blind source separation techniques. Once separated, the time interval between the A2 and P2 components is estimated with a time-centroid-based method. Experimental results using simulated data show excellent performance of the proposed algorithm to extract the A2 and the P2 components from the S2 sound and to estimate the time interval between them. Results obtained from real data are also encouraging and show promise for utilizing the proposed method in a clinical setting to non-invasively tract pulmonary hypertension.

Algorithms↗

PubMed2003

Relationships among spectral measures of baroreflex sensitivity and indices of cardiac vagal control.

Traditionally baroreflex sensitivity (BRS) has been assessed with pharmacological approaches such as phenylephrine infusion. Recently, non-invasive approaches using spectral analytic techniques have been employed to combine heart rate and blood pressure variability parameters to estimate BRS (the alpha index). Some authors have argued that BRS assessed at different frequencies of cardiovascular variabilities provide identical information and they should be combined into a single index of BRS based on total variability. The present study examined the relationship between BRS assessed using low, high, and total heart rate and blood pressure variabilities, and indices of cardiac vagal control assessed by standard spectral measures. Participants were 105 older male and female African-Americans who were part of the Healthy Aging In Nationally Diverse Longitudinal Samples (HANDLS) Study. Heart rate and blood pressure variabilities (HRV and BPV) were assessed using the Fast-Fourier Transform (FFT). The alpha index was computed as the square root of the ratio of low, high, or the mean of low and high frequency heart rate variability and the corresponding frequency ranges for systolic blood pressure variability. Correlations examining the relationships among BRS and various (e.g. log, normalized) indices of high frequency heart period variability (HF) were calculated for the total sample and by gender. Results indicated that the different BRS indices do not have the same relationship to all indices of HF. The results suggest that an aggregation of the power across bands is problematic at best, and indicates the need to examine the various frequency components separately.

Adult↗

PubMed2005

Cardiovascular variability during periodic leg movements: a spectral analysis approach.

OBJECTIVE: Changes in cardiovascular measures have been advocated as sensitive markers of phasic events arising from sleep. The current study was aimed to analyse the effects of periodic leg movements (PLMS) on heart rate variability (HRV) during NREM sleep in patients having restless legs syndrome and periodic leg movements during sleep. METHODS: The absolute and normalized high- and low-frequency peaks from spectral analysis (FFT) of R-R intervals, the HRV changes using wavelet transform, the geometric and time domain HRV were measured in 14 patients with restless legs syndrome and PLMS. The analysis was done comparing one hundred, 10 min periods with PLMS (PLMS+) and 60 periods without PLMS (PLMS-) in stage 2 of NREM sleep. In 8 patients analysis was also done in slow wave sleep (SWS). RESULTS: Occurrence of PLMS induced changes in geometrical indices of HRV, with a rise of the triangular index and the triangular interpolation of R-R intervals in PLMS+ periods (P < 0.0001). Small changes in time domain indices were found during PLMS+ periods, while the SD of the R-R intervals (SDNN), reflecting global HRV, was significantly higher (P = 0.001). While the low frequency (LF) power significantly increased in PLMS+ periods (P < 0.0001), high frequency (HF) power showed a weak and not significant reduction. The rise in sympathetic activity as detected by frequency domain HRV analysis was related to density and interval of PLMS. Comparison between sleep stages of NREM sleep demonstrated lower values of HRV measures when PLMS+ periods occur in SWS. CONCLUSIONS: Overall, PLMS occurrence was associated with a shift to increased sympathetic activity without significant changes in cardiac parasympathetic activity. The frequency domain analysis of HRV appears to be an easy tool to estimate the autonomic changes related to PLMS and PLMS- arousals and to differentiate their occurrence during stage 2 and deep sleep. SIGNIFICANCE: Spectral HRV measures may offer a simple approach to estimate the degree of autonomic changes occurring in relation to periodic leg movements in restless legs patients.

Adult↗

PubMed2006

Fluorobenzene-nucleobase interactions: hydrogen bonding or pi-stacking?

Studies on modified DNA oligomers and polymerase reactions have previously demonstrated that canonical nucleobases can exhibit stable and even selective pairing with shape-complementary fluorobenzene nucleotides. Because of the fluorination of the pairing edges, hydrogen bonds are believed to be absent, and the local DNA stability has been attributed to pi-stacking and shape complementarity. Using two-color resonant two-photon ionization and fluorescence emission spectroscopies, we show here that supersonically cooled complexes of the nucleobase analogue 2-pyridone with seven substituted fluorobenzenes (1-fluorobenzene, 1,2- and 1,4-difluorobenzene, 1,3,5- and 1,2,3-trifluorobenzene, 1,2,4,5- and 1,2,3,4-tetrafluorobenzene) are hydrogen-bonded and not pi-stacked. The S1 <--> S0 vibronic spectra show intermolecular vibrational frequencies that are characteristic for doubly hydrogen bonded complexes. The bands shift to the blue with increasing hydrogen-bond strength; the measured spectral blue shifts deltanu are in excellent agreement with the ab initio calculated shifts. The spectral shifts are also linearly correlated with the calculated hydrogen-bond dissociation energies D0, published in a companion paper (Frey, J. A.; Leist, R.; Leutwyler, S. J. Phys. Chem. A 2006, 110, 4188). This correlation allows us to reliably estimate the ground-state dissociation energies as D0 approximately 6 kcal/mol of the 2-pyridone.fluorobenzene complexes from the observed spectral shifts.

Fluorobenzenes↗

PubMed1993

Cardiac Doppler blood-flow signal analysis. Part 2. Time/frequency representation based on autoregressive modelling.

Doppler spectrograms obtained by using autoregressive (AR) modelling based on the Yule-Walker equations were investigated. A complex AR model using the in-phase and the quadrature components of the Doppler signal was used to provide blood-flow directions. The effect of model orders on the spectrogram estimation was studied using cardiac Doppler blood flow signals taken from 20 patients. The 'final prediction error' (FPE) and the 'Akaike's information criterion' (AIC) provided almost identical results in model-order selection. An index, the spectral envelope area (SEA), was used to evaluate the effect of window duration and sampling frequency on AR Doppler spectrogram estimation. The statistical analysis revealed that the SEA obtained from AR modelling was not sensitive to window duration and sampling frequency. This result verified the consistency of the AR Doppler spectrogram. The white-noise characteristics of the AR modelling error signal indicated that the Doppler blood-flow signal can be adequately modelled as a complex AR process. With appropriate model orders, AR modelling provided better Doppler spectrogram estimates than the periodogram.

Aortic Valve↗

PubMed1998

On derivation of spectral sensitivities of the human cones from trichromatic colour matching functions.

Despite the recent advance made by using the direct methods of retinal densitometry, microspectrophotometry and suction electrophysiology, the psychophysical approach based on colour matching data still remains an important source of accurate information about the spectral sensitivity of the cone photoreceptors in the human visual system. However, the commonly used technique of estimating cone sensitivities, based on the assumption that dichromacy is caused by the lack of one of the three types of the cone photoreceptors, requires the colour matching functions not only from trichromatic observers but from dichromats as well. Here we evaluate an alternative approach, originally put forward by Bongard and Smimov, that derives cone spectral sensitivities from colour matching functions only; without resorting to colour deficiency or any other data. When applied to CIE standard colour matching functions, this method yields curves of spectral sensitivities that are close to the classical Smith-Pokorny fundamentals, though the long-wave cone is shifted towards the short-wave region of the spectrum by 5 nm, as compared with Smith and Pokorny's results.

Color Perception↗

PubMed1999

IR investigation on dehydrophenylalanine containing model peptides in helical conformation deposited on a crystal surface

Fourier transform ir spectra have been recorded for three 3(10)-helical and one alpha-helical pentapeptides containing dehydrophenylalanine, in a thin solid film, in order to find marker bands for various secondary structures encountered in peptides containing dehydroaminoacids. The peptide solutions were deposited and dried as thin film on zinc selenide crystal surface. This convenient sampling method has provided reliable estimates of peptide secondary structure in solid state. Detailed vibrational assignments in the spectral region between 1200-1700 cm(-1) are reported. In this region, peptide amide I, II, and III vibrations occur. Spectra-structure correlation has been presented based on the amide modes. Comparison of the ir spectra with available crystal structure data provides qualitative support for assignments of ir bands to 3(10)-helical structure and alpha-helical structure in dehydrophenylalanine containing pentapeptides. Band frequency assignments for 3(10)-helical conformation are consistent for all three peptides. All the assignments agree closely with the theoretical predictions. The spectral differences between 3(10)-helical peptides and the alpha-helical peptide have been highlighted. These findings demonstrate that a method based on ir spectroscopy can be developed for a useful approximation of three-dimensional structure of dehydropeptides in solid state. Copyright 1999 John Wiley & Sons, Inc.

Journal Article↗

PubMed2004

Raman spectroscopic characterization of drying-induced structural changes in a therapeutic antibody: correlating structural changes with long-term stability.

We characterized the secondary structure of a therapeutic recombinant humanized monoclonal antibody (rhuMAb), formulated with different concentrations of sucrose, trehalose, and histidine and in solution, lyophilized, and spray-dried states. Quantitative secondary structure estimates were obtained using amide I band Raman spectroscopy and a previously developed spectral deconvolution procedure. On lyophilization or spray drying in the absence of sugar, the antibody underwent significant structural perturbation. The beta-sheet content decreased with corresponding gain in the turn and unordered content. With increasing amount of sucrose or trehalose, the extent of structural perturbation decreased. Eventually, at sugar-to-protein molar ratios of > or =360, almost complete structural preservation was observed. Histidine also protected the antibody against lyophilization-induced structural changes. The extent of structural perturbation immediately after lyophilization or spray drying exhibited good correlation with the rate of aggregation for the antibody during long-term storage under accelerated conditions. The results demonstrate that amide I band Raman spectroscopy could be a quick and reliable way to screen excipients and their concentrations during lyophilized or spray dried formulation development.

Antibodies, Monoclonal↗

PubMed1980

trans-Cinnamic acid--alpha-cyclodextrin system as studied by solubility, spectral, and potentiometric techniques.

Complex formation in aqueous solutions of trans-cinnamic acid or trans-cinnamate ion (the substrate, S) and alpha-cyclodextrin (the ligand, L) can be described quantiatively as the 1:1 and 1:2 complexes, SL and SL2. The solubility, spectral, and potentiometric data over a wide range of ligand concentrations yielded consistent estimates of the complex association constants. For cinnamic acid at 25 degrees K11 = 2260 M-1, delta H degree 11 = 9.3 kcal/mole, and delta S degree 11 = -8 e.u.; and K12 = 60 M-1, delta H degree 12 = -12 kcal/mole, and delta S degree 12 = -26 e.u. For cinnamate ion at 25 degrees, K11 = 110 M-1, delta H degree 11 = -1.9 kcal/mole, and delta S degree 11 = +11 e.u.; and K12 = 15 M-1, delta H degree 12 = 9 kcal/mole, and delta S degree 12 = -15 e.u. (all entrophy changes are unitary quantities). Thermodynamic cycles for the complexes, using solubility data, reveal that complex formation in the solid phase is thermodynamically spontaneous but that complex stability is greater in ageous solution than in the solid phase.

Chemical Phenomena↗