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PubMed2000

Role of reactive oxygen intermediates in the decrease of hepatic cytochrome P450 activity by serum of humans and rabbits with an acute inflammatory reaction.

Serum of rabbits with a turpentine-induced acute inflammatory reaction (RS(INFLA)) and serum of humans with a viral infection (HS(INF)) were previously shown to diminish hepatic cytochrome P450 (P450) content and activity. To document the role of reactive oxygen intermediates in the serum-mediated decrease in P450 content and activity, hepatocytes of rabbits with an acute inflammatory reaction (H(INFLA)) were incubated with RS(INFLA) and HS(INF) for 4 h, and total P450 content (spectrally measurable P450), P450 activity (assessed by estimating the formation of theophylline metabolites), and amount of CYP1A1, CYP1A2, and CYP3A6 proteins were measured. RS(INFLA) or HS(INF) decreased P450 content and activity without affecting the amount of CYP1A1 and -1A2 H(INFLA). Exposure of H(CONT) or H(INFLA) to hydrogen peroxide (0.01-1.0 mM) and sodium nitroprusside (0.01-1.0 mM) produced a dose-dependent decrease in P450 content and in the formation of theophylline metabolites without modifying the amount of CYP1A1 and CYP1A2, whereas lipid peroxidation increased. Incubation of L-NAME (0.05-1.0 mM), dimethylthiourea (6.25-50 mM), or N-acetylcysteine (0.01-1.0 mM) with H(INFLA) partially prevented the decrease in P450 content and activity and the increased lipid peroxidation induced by RS(INFLA) and HS(INF). On the other hand, 3-amino-1,2,4-triazole (10-100 mM) or diethyldithiocarbamate (1.0-10 mM) potentiated RS(INFLA)- and HS(INF)-mediated decreases in P450 content and activity and the increase in lipid peroxidation, without affecting the amount of CYP1A1 or -1A2; DL-buthionine-(S,R)-sulfoximine (2.5-25 mM) potentiated only the inhibition of 1,3-dimethyluric acid formation. It is concluded that reactive oxygen intermediates are implicated in the decrease of H(INFLA) P450 content and activity induced by 4 h of exposure to RS(INFLA) or HS(INF).

Acute-Phase Reaction↗
PubMed2001

Neonatal magnetocardiography and Fourier spectral analysis.

OBJECTIVE: In this study we investigated the relationship between heart rate variability (HRV) and respiration in healthy and probably asphyxiated infants using magnetocardiographic (MCG) recordings. METHODS: Ten healthy and eight infants from pregnancies complicated by preeclampsia with indications of mild perinatal asphyxia were included in the study. All were near term. Maternal age ranged from 16 to 39 years (mean = 29.05, SD = 6.13). Spectral analysis was used to find out any association between respiration and HRV. RESULTS: Respiratory sinus arrhythmia (RSA) was reduced in preeclamptic infants with indications of mild perinatal asphyxia. This difference was statistically significant (p < 0.0002, t-test), whereas the heart rate of the two groups was not statistically significant (p = 0.1, t-test). CONCLUSION: The results suggest that infants with indications of mild preeclampsia differ from controls in respiratory activity and this difference is independent of basal heart rate. Thus, spectral analysis could be useful for the estimation of influence of mild perinatal asphyxia in the RSA rhythm of newborns.

Asphyxia Neonatorum↗
PubMed1992

[An analysis of the autonomic manifestations of Raynaud's phenomenon by the spectrum of heart rhythm variability].

A study was made of the specificity of segmental and suprasegmental vegetative disorders seen in patients with Raynaud's phenomenon (RP). The sympathetic-parasympathetic interrelations were estimated according to the dynamics of the spectral constituents of heart rhythm under different functional conditions. There was a decrease of the sympathetic activity modulated by the stem and segmental mechanisms, accompanied by activation and rigidity of the suprasegmental ergotropic systems, leading to a stable vasospasm on the periphery. This may determine the low efficacy of vegetotropic peripheral drugs and a higher therapeutic effect of psychotropic drugs which reduce ergotropic activation.

Autonomic Nervous System Diseases↗
PubMedDate not supplied

[From determination of amino acid residue conformation to reconstruction of the spatial structure of proteins (from the data of nuclear Overhauser enhancement spectroscopy].

A new approach to the calculation of the spatial protein structure based on the joint utilization of the theoretical conformational analysis method and nuclear Overhauser enhancement (NOE) spectroscopy data is proposed and verified. The quality in determining various molecule structural parameters is estimated in terms of the expected NOE spectral parameters derived from the X-ray analysis data of the avian pancreatic polypeptide. The proposed approach is shown to correctly determine such structural parameters of protein molecules as local amino acid residue conformations, reciprocal spatial orientation of the C alpha atoms neighbouring along amino acid sequence and reapproached segments of the polypeptide chain. Spatially remote molecule fragments are mainly responsible for the error in determining structural parameters.

Amino Acids↗
PubMed1985

[Periodic changes in evoked mediator secretion at the neuromuscular synapse].

Extra- and intracellular recordings of the frog m. sartorius postsynaptic potentials with low concentration of Ca2+ ions (0.2-0.6 mmol/l) aided to study the dynamics of quanta transmitter release in prolonged motor nerve stimulation (0.5-10.0 imp/s). The statistical analysis showed that with intracellular recording only, time intervals between transmitter release were distributed in an evenly manner. Estimation of the correlation function and the spectral density revealed the periodical fluctuations of evoked transmitter release with periods from a few seconds to 1-2 min. With intracellular recording, oscillations of the transmitter release occurred in about 1/3 of cases whereas with extracellular recording they were always present. Analyses of a single release site activity by means of two extracellular electrodes inserted into a single nerve terminal, showed considerable changes of the cyclic transmitter secretion. The evoked transmitter release in a single release site seems to fluctuate periodically.

Animals↗
PubMed1983

Hydrogenosomal ferredoxin of the anaerobic protozoon, Tritrichomonas foetus.

A low molecular weight iron-sulfur protein has been purified from Tritrichomonas foetus by deoxycholate extraction of whole cells, ion exchange chromatography, and gel filtration. The purified protein was essentially homogeneous as judged by isoelectric focusing, polyacrylamide gel electrophoresis, and gel filtration. A pI of 4.3 was observed. The molecular weight of the protein was estimated to be 12,000. Chemical and spectral analysis showed the protein to have a [2Fe-2S] cluster. The absorbance spectrum of the oxidized protein showed maxima at 280, 340, 458 and shoulders at 410 and 550 nm. The maximum observed A458/A280 ratio was 0.82 and the absorbance of the oxidized protein at 458 nm was 8,000 M-1 X cm-1. The low temperature EPR spectrum of the protein reduced with dithionite revealed axial symmetry with features at g values of g = 1.94 and g = 2.02. The oxidized protein gave no EPR signal in the g = 1.8 to 2.2 range. Cell fractionation studies indicated the localization of this protein in the hydrogenosome. The protein was able to function as an electron transport component in the reduction of metronidazole (a 5-nitroimidazole derivative) by pyruvate:ferredoxin oxidoreductase and hydrogenase from T. foetus and also from Trichomonas vaginalis and Clostridium pasteurianum as well as in the reduction of cytochrome c by plant NADPH:ferredoxin oxidoreductase. This protein has the characteristics of a ferredoxin and is likely to be a physiological electron carrier in hydrogenosomal pyruvate oxidation.

Anaerobiosis↗
PubMed1996

[Determining the degree of stenosis of peripheral arteries. Hemodynamic and ultrasound principles].

With colour duplex sonography, the identification and quantification of arterial stenoses in peripheral arteries had become feasible in reasonable time. However, the haemodynamic considerations are more complicated in peripheral arteries than in carotid arteries. This is attributable to the much longer vessel length, the influences of peripheral resistance, the frequency of multiple stenoses and combinations of occlusion and stenosis with multiple collateral vessels. Different qualitative and quantitative approaches are used: b-mode sonography, spectral analysis, velocity measurements, continuity equation and estimation of systolic pressure gradients (Bernoulli equation). Although standardized criteria in the grading of stenoses are not commonly used, the peak velocity ratio (PVR as a ratio of intra-and prestenotic velocity) seems to be mathematically founded, usefully versatile and reliable.

Arterial Occlusive Diseases↗
PubMed2006

Spatial and temporal changes of upper trapezius muscle fiber conduction velocity are not predicted by surface EMG spectral analysis during a dynamic upper limb task.

The purpose of the study was to examine the temporal and spatial correlation between estimates of trapezius muscle fiber conduction velocity (CV) and surface EMG instantaneous mean power spectral frequency (iMPF) during dynamic movement of the upper limb. Surface EMG signals were detected from the upper division of the trapezius muscle in 13 healthy volunteers using linear arrays of eight electrodes at three locations in the cephalad-caudal direction. Subjects were asked to tap with their hands in a cyclic manner between targets positioned mid thigh and 120 degrees of shoulder flexion, to the beat of a metronome set at 88 beats per minute for 5 min. Muscle fiber CV and iMPF were estimated for each cycle at the time instant corresponding to 90 degrees of shoulder flexion. Non-significant correlations were identified between CV and iMPF initial values (R(2)=0.03-0.01), rate of change over time (R(2)=0.10-0.004) and normalized rate of change (R(2)=0.12-0.01) at all three locations on the upper trapezius muscle. These results demonstrate that both spatial and temporal variations in trapezius muscle fiber CV are not predicted by EMG spectral analysis during dynamic movement of the upper limb. This finding suggests that spectral analysis cannot be used to infer changes in the spatial and temporal behavior of muscle fiber CV during dynamic tasks.

Adult↗
PubMed2002

Estimation of chlorophyll concentration in lakes and inland seas with a field spectroradiometer above the water surface.

The estimation of chlorophyll concentration in the water by use of a field spectroradiometer above the water surface is necessary for the removal of the effect of specular reflection at the water surface. The amount of specular reflection from the water surface was assessed on the basis of the spectral signature data that was measured above and below the water surface. Furthermore, a method to remove the effect of specular reflection from spectral signature data that was measured above water surface was proposed. Finally, chlorophyll-a concentration was estimated accurately from the spectral signature measured by field spectroradiometer above water surface with the proposed surface reflection model.

Journal Article↗
PubMed2004

Introducing a baroreflex model for studying cardiovascular effects of mental workload.

A quantitative baroreflex control model is presented aimed at estimating differences in autonomic activation due to mental task performance. The model, which builds on earlier work of Wesseling and colleagues, is strongly supported by well-established knowledge of physiological control processes. Spectral measures of heart rate and blood pressure variability provide the information to estimate autonomic gain and tone parameters. The article gives a detailed model description as well as an evaluation in terms of spectral variability distributions, respiratory sinus arrhythmia, and vagal control mechanisms. The estimation procedure is outlined while presenting two studies that describe the effects of mental workload and vagal blockade, respectively. It is concluded that, using the model approach, cardiovascular effects of mental task performance can be interpreted in terms of specific changes in autonomic state. The model is implemented in a Matlab/Simulink environment and is available for other researchers in the field.

Adult↗
PubMed1975

Interaction of aflatoxin B1 with DNA.

The interaction of aflatoxin B1 with DNA was investigated. In the presence of native DNA the absorption spectrum of the toxin showed an obvious spectral shift in the region of 300-420 nm with an isosbestic point at 376 nm. DNA-bound aflatoxin is hydrolyzed in alkaline media more easily than the free toxin. The hydrolized form has a labile structure and can decompose further. The bound toxins are easily dissociated by heat as well as by salt, and all toxin molecules are released from DNA which remains double-stranded. Aflatoxin can bind to thermally denatured DNA as well, with an accompanying spectral shift which depends on the particular preparation of denatured DNA, and there was an isosbestic point at 380 nm. The complex of toxin and denatured DNA was stabilized by salt up to 0.1 M. Thus it was concluded that aflatoxin was bound with denatured DNA in a different form from native DNA. The number of binding sites of DNA was estimated by constructing Scatchard plots based on both spectral analysis and equilibrium dialysis. However, these show no definite value but fall in the region of 0.07 to 0.013, that is one toxin molecule per 80-140 nucleotide of native DNA. Several lines of evidence suggest the possibility that aflatoxin exists in aqueous solution as aggregates. The mechanism of the binding was discussed. It is noteworthy that the number of binding sites of DNA doubles by the presence of histones.

Aflatoxins↗
PubMed1986

Simulation of real-time frequency estimators for pulsed Doppler systems.

Four time-domain oriented, real-time frequency estimators, based on the detection of phase, zero-crossings, instantaneous frequency or autocorrelation, were simulated on a digital computer and subjected to computer generated Doppler signals, enabling the investigation of the influence of spectral shape, filtering, frequency shift, noise and quantitation. Three estimators, the autocorrelator as well as the instantaneous frequency detector and the autocorrelator, both with extended frequency range, appeared to be very accurate. They exhibit a bias in the estimator output of less than 2 percent over a wide frequency range, the former up to nearly the Nyquist frequency, the latter two beyond, even for skew spectra and under poor signal conditions regarding bandwidth and noise.

Blood Flow Velocity↗
PubMed1984

Cadmium binding to metallothioneins and the estimation of protein concentration using cadmium-saturation methods.

The detailed spectral changes observed in the absorption, circular dichroism (CD) and magnetic circular dichroism (MCD) spectra upon addition of Cd2+ to rat liver Cd,Zn-metallothionein (MT) are reported. Results from dialysis experiments clearly demonstrate that up to 8.6 mole equivalents of Cd2+ can be bound to this protein. The excess Cd2+ ions bound appear to have lower binding constants than those of the first seven Cd2+ ions bound. Red blood cell hemolysate (RBC) can compete with the metallothionein for all Cd2+ bound in excess of seven mole equivalents. Thus the RBC hemolysate method of estimating protein concentrations is shown to be correct when based upon complete loading of all binding sites in MT with Cd2+.

Animals↗
PubMed1999

Stochastic resonance in threshold systems.

We consider signal processing in simple threshold systems with nonstationary additive and/or multiplicative noise. A discrete-time process with a small periodical signal masked by noise represents an input. The systems convert sampled input data to a nonstationary random point event flow carrying some information on an input signal. As it is shown in our previous study [M.M. Alibegov, Astron. Lett. 22, 564 (1996)], the Rayleigh spectral function of a random point event train estimates a signal-to-noise ratio (SNR) at selected frequencies. Based on these results, we compute a system response at signal frequencies as a function of threshold and input noise intensity. The threshold systems are shown to reveal stochastic resonance (SR), i.e., output SNR exhibits a maximum at resonant noise intensity (intensities) and threshold(s) at rather common conditions. We show that SR and Rayleigh spectral technique allow us to carry out numerical signal detection in data sets with noise.

Journal Article↗
PubMed1990

Computer evaluation of Doppler spectral envelope area in patients having a valvular aortic stenosis.

The reliability of three algorithms to estimate the maximal and minimal frequency contours of Doppler spectrograms was evaluated in a group of 48 patients. Two algorithms had previously been used in the literature. These are the Modified Threshold Crossing Method and the Hybrid method. The third algorithm is new and is the Maximal Background Noise Threshold Crossing Method. A new approach was also proposed in the present study to estimate the background noise level of Doppler spectrograms. This level was used as a threshold in the computation of the spectral envelopes. Two diagnostic spectral parameters (the spectral envelope area and the systolic velocity integral) extracted from Doppler spectrograms recorded in the left ventricular outflow tract were also evaluated and tested to discriminate between 23 patients having no aortic pressure gradient and 25 patients with a stenotic aortic valve. Results describe the influence of the threshold level used in the Modified Threshold Crossing Method and the Hybrid method on the variability of the spectral contours. It is clearly demonstrated that the variability of minimal frequency contours is higher than that of maximal frequency contours. All three algorithms provided similar diagnostic performances with the spectral envelope area (71% to 73% of correct classifications) while the Maximal Background Noise Threshold Crossing Method and the Hybrid method provided the best results for the systolic velocity integral (69% of correct classifications). Because the systolic velocity integral combined with the continuity equation is used in the literature to evaluate noninvasively the aortic valve area, these results suggest the use of the spectral envelope area instead of the systolic velocity integral.

Aged↗
PubMed1988

A new method of presentation of the average spectral properties of the EEG time series.

In framework of the AR model the transfer function and the impulse response function of the EEG time series were found. The parameters of the impulse response function were interpreted in terms of: frequencies, damping factors and amplitudes of the hypothetical brain rhythm generators. The method of the rhythm diagrams was proposed to describe the spectral properties of the EEG time series. It makes possible the accurate estimation of the EEG rhythm's frequencies and their intensities, especially weak components hardly visible in the conventional spectral analysis are well distinguished. Rhythm diagrams can be a useful tool in the clinical applications and offer new possibilities in the direct comparison of the results of modeling with the experimental data.

Animals↗
PubMed1984

Speech coding in the auditory nerve: II. Processing schemes for vowel-like sounds.

Several processing schemes by which phonetically important information for vowels can be extracted from responses of auditory-nerve fibers are analyzed. The schemes are based on power spectra of period histograms obtained in response to a set of nine two-formant, steady-state, vowel-like stimuli presented at 60 and 75 dB SPL. One class of "local filtering" schemes, which was originally proposed by Young and Sachs [J. Acoust. Soc. Am. 66, 1381-1403 (1979)], consists of analyzing response patterns by filters centered at the characteristic frequencies (CF) of the fibers, so that a tonotopically arranged measure of synchronized response can be obtained. Various schemes in this class differ in the characteristics of the filter. For a wide range of filter bandwidths, formant frequencies correspond approximately to the CFs for which the response measure is maximal. If in addition, the bandwidths of the analyzing filters are made compatible with psychophysical measures of frequency selectivity, low-frequency harmonics of the stimulus fundamental are resolved in the output profile, so that fundamental frequency can also be estimated. In a second class of processing schemes, a dominant response component is defined for each fiber from a 1/6 octave spectral representation of the response pattern, and the formant frequencies are estimated from the most frequent values of the dominant component in the ensemble of auditory-nerve fibers. The local filtering schemes and the dominant component schemes can be related to "place" and "periodicity" models of auditory processing, respectively.

Animals↗
PubMed1997

Sleep and circadian influences on cardiac autonomic nervous system activity.

To assess the separate contributions of the sleep and circadian systems to changes in cardiac autonomic nervous system (ANS) activity, 12 supine subjects participated in two 26-h constant routines, which were counterbalanced and separated by 1 wk. One routine did not permit sleep, whereas the second allowed the subjects to sleep during their normal sleep phase. Parasympathetic nervous system activity was assessed with respiratory sinus arrhythmia as measured from the spectral analysis of cardiac beat-to-beat intervals. Sympathetic nervous system activity was primarily assessed with the preejection period as estimated from impedance cardiography, although the 0.1-Hz peak from the spectral analysis of cardiac beat-to-beat intervals, the amplitude of the T wave in the electrocardiogram, and heart rate were also measured. Respiratory sinus arrhythymia showed a 24-h rhythm independent of sleep, whereas preejection period only showed a 24-h rhythm if sleep occurred. Thus the findings indicate that parasympathetic nervous system activity is mostly influenced by the circadian system, whereas sympathetic nervous system activity is mostly influenced by the sleep system.

Adult↗