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At least 1,081 records · Page 60Linked to original sources
PubMed1993

Evidence for more than one type of non-NMDA receptor in outside-out patches from cerebellar granule cells of the rat.

1. Application of non-NMDA (non-N-methyl-D-aspartate) receptor agonists onto outside-out patches of cerebellar granule cells gave two characteristic types of response (in different patches) which we have referred to as 'high conductance' and 'low conductance' responses. At a qualitative level these patches could be readily distinguished by the size of the noise increase accompanying their membrane currents. 2. In high conductance patches both AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) and kainate gave discrete single-channel conductances (10-30 pS), while in low conductance patches, AMPA produced small discrete events (6-10 pS), and kainate opened channels with conductances too small to be directly resolved. All patches examined contained NMDA receptor channels with characteristic 50 and 40 pS conductance levels. 3. Despite the marked differences in single-channel conductances, kainate dose-response curves constructed for high and low conductance patches had similar EC50 values of approximately 150 microM. 4. Spectral analysis of low conductance kainate responses gave an estimated channel conductance of approximately 1.5 pS. In these same low conductance patches AMPA produced discrete openings with two conductance levels; their mean conductances (and relative proportions) were 6 (87%) and 10 pS (13%). 5. In high conductance patches, glutamate (10-30 microM), AMPA (3-10 microM), and kainate (10-30 microM), each activated non-NMDA channels with three multiple conductance levels. The amplitudes of these conductance levels (approximately 10, 20 and 30 pS) were similar for each of the agonists, and their relative proportions (i.e. areas in the amplitude histograms) were constant for all three agonists. In addition, the relative proportion of levels was constant between patches, and all three levels were invariably present. These observations are all consistent with the idea that the three multiple conductances originate from a single receptor channel, activated by AMPA, kainate and glutamate. 6. Non-NMDA single-channel current-voltage (I-V) plots showed outward rectification in high conductance patches. For all three multiple conductance levels the ratio of outward to inward single-channel slope conductance was 1.8 +/- 0.1 and this rectification remained present in symmetrical Na+ solutions. 7. In high conductance patches, the events produced by a rapid application of 20-50 microM glutamate were compared with those activated during steady-state application.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Determination of airway and tissue resistances after antigen and methacholine in nonhuman primates.

Antigen challenge of Ascaris suum-sensitive animals has been used as a model of asthma in humans. However, no reports have separated total respiratory resistance into airway (Raw) and tissue (Rti) components. We compared input impedance (Zin) and transfer impedance (Ztr) to determine Raw and Rti in anesthetized cynomolgus monkeys under control and bronchoconstricted conditions. Zin data between 1 and 64 Hz are frequency dependent during baseline conditions, and this frequency dependence shifts in response to A. suum or methacholine. Thus it cannot be modeled with the DuBois model, and estimates of Raw and Rti cannot be determined. With Ztr, baseline data were much less variable than Zin in all monkeys. After bronchial challenge with A. suum or methacholine, the absolute amplitude of the resistive component of Ztr increased and its zero crossing shifted to higher frequencies. These data can estimate Raw and Rti with the six-element DuBois model. Therefore, in monkeys, Ztr has advantages over other measures of lung function, since it provides a methodology to separate estimates of Raw and Rti. In conclusion, Ztr shows spectral features similar to those reported in healthy and asthmatic humans.

Air Pressure↗
PubMed1997

Color Doppler echocardiographic evaluation of tricuspid regurgitation and systolic pulmonary artery pressure in the full-term and preterm newborn.

Color Doppler echocardiography of tricuspid valve regurgitation (TR) is a valid, noninvasive method of determining systolic pulmonary artery pressure (SPAP). In a prospective study the authors examined 56 healthy full-term newborns (group I), 36 healthy preterm newborns (group II), and 10 preterm newborns with severe respiratory distress syndrome requiring surfactant replacement therapy (group III). Doppler studies were repeated until the transtricuspid gradient was < 20 mm Hg. In 83.3% of children a reproducible spectral curve was recorded at least once. The authors estimated the transtricuspid gradient delta p (RV-RA) by using the modified Bernoulli equation. Within the first twenty-four hours delta p (RV-RA) was < 20 mm Hg in 72.7%, 50%, and 25% of children with measurable TR in groups I, II, and III, respectively, increasing to 91.1%, 78.6%, and 55.6% within forty-eight hours. There was no significant correlation between SPAP and gestational age, birth weight, mode of delivery, and ductal closing time. Continuous holosystolic envelope tracing of TR was recorded in 16.6%. In these patients delta p (RV-RA) was measured markedly higher (mean of 30.1 mm Hg) than in the others (mean 17.3 mm Hg). The authors conclude that there is a high prevalence of TR in neonates, which allows estimation of SPAP in > 80% of newborns without considerable impairment. Normalization of SPAP takes place within four days in most patients, but there is a delay in preterm infants with severe respiratory distress syndrome.

Blood Pressure↗
PubMed2000

Characterization of natural illuminants in forests and the use of digital video data to reconstruct illuminant spectra.

We describe illumination spectra in forests and show that they can be accurately recovered from recorded digital video images. Natural illuminant spectra of 238 samples measured in temperate forests were characterized by principal-component analysis. The spectra can be accurately approximated by the mean and the first two principal components. Compared with illumination under open skies, the loci of forest illuminants are displaced toward the green region in the chromaticity plots, and unlike open sky illumination they cannot be characterized by correlated color temperature. We show that it is possible to recover illuminant spectra accurately from digital video images by a linear least-squares-fit estimation technique. The use of digital video data in spectral analysis provides a promising new approach to the studies of the spatial and temporal variation of illumination in natural scenes and the understanding of color vision in natural environments.

Color↗
PubMedDate not supplied

[Use of x-ray spectral microanalysis for studying mineralized tissues].

In microanalysis of mineralized tissues an x-ray spectral method possessed an absolute limit of sensitivity about 5-10 minus 15 g. A relative limit of the method sensitivity constituted hundredth parts of a per cent and locality of the analysis--several cubic microns. The x-ray spectral microanalysis permitted to carry out qualitative and quantitative estimations of content of elements in different structures of biological tissues. The data were obtained on content of calcium and phosphorus in compact part of human tubular bone.

Adult↗
PubMed2006

Noise reduction for doppler ultrasound signal based on the adapted local cosine transform and the garrote thresholding method.

In this paper, a novel approach, using the adapted local cosine transform combined with the non-negative garrote thresholding, is proposed to remove noise from the Doppler ultrasound signal. In the proposed approach, the local cosine transform is first performed on the signal of interest followed by a search algorithm to select the best basis. Then the coefficients of the obtained best basis are thresholded based on the non-negative garrote thresholding method. By means of the thresholded coefficients of the best basis, the signal is reconstructed. In the simulation study, the estimation precisions of the mean frequency waveform and the spectral width waveform are studied for the signal after denoising. The simulation and clinical results have shown that the proposed approach is superior to ones based on the wavelet transform, especially under low signal-to-noise ratio (SNR) circumstances.

Algorithms↗
PubMedDate not supplied

[Ultrasound monitoring of the course of uveal melanoma].

Fifty-two persons were examined to define a role of a current ultrasound study during monitoring the natural history of uveal melanoma. The B-mode ultrasonography, color Doppler imaging and power Doppler and Doppler spectral study were applied. Ultrasound densitometry was used to estimate 326 sonograms imaging melanoma. Control studies assessed the time course of metric, hemodynamic, vascular, and densitometric changes of the tumor during organ-saving treatment. A number of ultrasound criteria for the positive and negative course of the disease were defined. Emphasis is focused on the sign that turned out to be most resistant to medical measures. The author shows it necessary to comprehensively use all currently available ultrasound diagnostic techniques for effective monitoring the state of uveal melanoma.

Brachytherapy↗
PubMed1987

In vivo noninvasive observation of acute mesenteric ischemia in rats.

Acute intestinal ischemia remains a catastrophic event even with the advent of modern diagnostic and vascular surgical techniques. An early noninvasive test would be valuable since early operation yields better survival rates. We have used an in vivo rat model to study acute intestinal ischemia after occlusion of the superior mesenteric artery (SMA). 31Phosphorus magnetic resonance spectroscopy (MRS), a noninvasive nondestructive technique, can detect the phosphorus metabolites most likely to be altered in ischemia: adenosine triphosphate, phosphocreatine (PCr), inorganic phosphate (Pi) and phosphomonoesters and phosphodiesters. Furthermore, intracellular pH can be estimated from the pH dependent position of the Pi spectral line relative to PCr. A tourniquet was loosely placed around the SMA in five Wistar rats through a transabdominal approach to the retroperitoneum. The abdomen was immediately closed. A 20 millimeter MRS surface coil was placed on the abdomen and 31Phosphorus spectra were accumulated. The SMA was then occluded and additional 31Phosphorus spectra were taken for the next 75 minutes. Significant (p less than 10(-4) changes in the position and magnitude of the spectra lines occurred within 20 minutes; the Pi position indicates severe intracellular acidosis and rapidly increases to three times its original magnitude. The PCr line decreases in magnitude. In a similar experiment, occlusion of the superior mesenteric vein (SMV) produced equivalent results. Occlusion of vessels other than the SMA or SMV not accompanied by transmural ischemia resulted in spectra unaltered from control. These findings support the application of phosphorus MRS to clinical studies.

Adenosine Triphosphate↗
PubMed1976

[Psychophysiological studies of EEG, operational performance and the dynamics of vigilance regulation. II. EEG activity and reactivity during tracking performance in a control loop with varying degrees of difficulty (author's transl)].

In ten male students the EEG occipital activity was recorded during a visuo-motor task consisting of pursuit-tracking. The degree of task difficulty varied systematically depending on the modification of the transfer function of control element dynamics. The EEG data were evaluated by serial spectral analysis. The distribution functions of the total power estimates and their minima and maxima reflect the dynamics of the regulation of cortical vigilance and permit to differentiate the degree of effort which corresponds to the varying degree of task difficulty. The study of task-irrelevant acoustically evoked potentials showed that with increasing cortical activation the amplitudes of N1-P2 and P2-N2 are diminished. These results might suggest that evoked potentials induced by task-irrelevant stimuli can serve as indicators of the neuronal capacity available for information processing that is not task-oriented.

Adult↗
PubMedDate not supplied

[Automatic regulation of sinus rhythm in patients with migraine].

The clinical symptoms of migraine point to autonomic disturbances, especially to disrupted regulation of the circulatory system and autonomic balance. Searching for more accurate autonomic system studies we turned to the spectral analysis of cardiac rhythm changes, that allows to estimate the autonomic balance in sinus node. 44 patients with migraine were studied and the results were compared with those obtained in 74 healthy subjects. The reduced influence of both sympathetic and parasympathetic part of autonomic system on the sinus rhythm in migraine patients was found. The autonomic balance is shifted to the parasympathetic innervation side in patients with migraine.

Adolescent↗
PubMed2003

Contributions of short-lived radioiodines to thyroid doses received by evacuees from the Chernobyl area estimated using early in vivo activity measurements.

A series of in vivo gamma spectrometric measurements of 65 people evacuated from Pripyat 1.5 days after the Chernobyl Nuclear Power Plant Unit 4 explosion was performed in St Petersburg, Russia, as early as 30 April 1986. The historical spectra and interviews were recently processed and the results used for thyroid dose estimation. Activities of 131I in thyroid and 132Te in lungs were determined easily; for estimation of 132I and 133I activities in thyroid, sophisticated methods of spectral processing were developed. According to thyroid measurement data, the mean ratio of 133I/131I activities (at the time of the accident) inhaled by residents of Pripyat was 2.0. The mean ratio of thyroid dose from 133I inhalation to that caused by 131I amounts to 0.3, which confirms the accuracy of dose estimates based on the evolution of the Chernobyl accident. The mean ratio of 132I activity in thyroid to that of 132Te in lungs was assessed from the human measurement data to be 0.2, which is in reasonable agreement with the metabolic properties of these radionuclides. The mean ratio of thyroid dose from 132I originating from 132Te deposited in lungs to the dose caused by 131I was 0.13 +/- 0.02 for Pripyat residents who did not take KI pills and 0.9 +/- 0.1 for persons who took KI pills. Thus, the contribution of short-lived radioiodines to total thyroid dose of Pripyat residents, which was on average 30% for persons who did not use stable iodine prophylaxis, and about 50% for persons who took KI pills on 26-27 April, should be accounted for in the assessment of thyroid health effects.

Air Pollutants, Radioactive↗
PubMed2003

Relationships between leaf chlorophyll content and spectral reflectance and algorithms for non-destructive chlorophyll assessment in higher plant leaves.

Leaf chlorophyll content provides valuable information about physiological status of plants. Reflectance measurement makes it possible to quickly and non-destructively assess, in situ, the chlorophyll content in leaves. Our objective was to investigate the spectral behavior of the relationship between reflectance and chlorophyll content and to develop a technique for non-destructive chlorophyll estimation in leaves with a wide range of pigment content and composition using reflectance in a few broad spectral bands. Spectral reflectance of maple, chestnut, wild vine and beech leaves in a wide range of pigment content and composition was investigated. It was shown that reciprocal reflectance (R lambda)-1 in the spectral range lambda from 520 to 550 nm and 695 to 705 nm related closely to the total chlorophyll content in leaves of all species. Subtraction of near infra-red reciprocal reflectance, (RNIR)-1, from (R lambda)-1 made index [(R lambda)(-1)-(RNIR)-1] linearly proportional to the total chlorophyll content in spectral ranges lambda from 525 to 555 nm and from 695 to 725 nm with coefficient of determination r2 > 0.94. To adjust for differences in leaf structure, the product of the latter index and NIR reflectance [(R lambda)(-1)-(RNIR)-1]*(RNIR) was used; this further increased the accuracy of the chlorophyll estimation in the range lambda from 520 to 585 nm and from 695 to 740 nm. Two independent data sets were used to validate the developed algorithms. The root mean square error of the chlorophyll prediction did not exceed 50 mumol/m2 in leaves with total chlorophyll ranged from 1 to 830 mumol/m2.

Algorithms↗
PubMed1978

[Detection of estrogen residues in meat by thin layer chromatography and fluorimetry (author's transl)].

A new method for the qualitative and quantitative determination of six anabolic substances is described. The analytical procedure consists of the following steps: comminution of the meat sample; homogenisation with tetrahydrofurane; liquid-liquid partition between sodium hydroxide solution and petroleum ether/benzene; chromatography of the estrogen containing fraction on Sephadex LH-20; derivatization with Dansyl chloride; and finally thin layer chromatography. The qualitative estimation on the TLC-plate is performed with 366 nm ultra violet light. The quantitative determination is carried out either by fluorimetry after elution of the substances from the plate, or by means of a remission spectral fluorimeter directly on the plate. The detection limit of the qualitative estimation in meat extracts was 5--10 ppb. A minimum concentration of 20--50 ppb is necessary for quantitative determination.

Animals↗
PubMed1994

Autonomic changes during hypnosis: a heart rate variability power spectrum analysis as a marker of sympatho-vagal balance.

Spectral analysis of beat-to-beat variability in electrocardiography is a simple, noninvasive method to analyze sympatho-vagal interaction. The electrocardiogram is analyzed by means of an automatic, autoregressive modeling algorithm that provides a quantitative estimate of R-R interval variability by the computation of power spectral density. Two major peaks are recognizable in this specter: a low-frequency peak (LF, -0.1 Hz), related to the overall autonomic activity (ortho+parasympathetic) and a high-frequency peak (HF, -0.25 Hz), representative of the vagal activity. The LF/HF ratio is an index of the sympatho-vagal interaction. This technique was applied, using a computer-assisted electrocardiograph, to 10 healthy volunteers (6 high and 4 low hypnotizable subjects as determined by the Stanford Hypnotic Susceptibility Scale, Form C) in randomized awake and neutral hypnosis conditions. Preliminary results indicated that hypnosis affects heart rate variability, shifting the balance of the sympatho-vagal interaction toward an enhanced parasympathetic activity, concomitant with a reduction of the sympathetic tone. A positive correlation between hypnotic susceptibility and autonomic responsiveness during hypnosis was also found, with high hypnotizable subjects showing a trend toward a greater increase of vagal efferent activity than did low hypnotizables.

Adult↗
PubMed1988

Estimate of attenuation coefficient for ultrasonic tissue characterization using time-varying state-space model.

The images generated from ultrasound pulse-echo signals have long been used to aid clinical diagnosis. Recently, there has been a growing interest in quantitatively determining the acoustic parameters of the tissue as a means of classification and diagnosis. For example, the frequency-dependent attenuation is known to be correlated with different diseases in the liver. In this paper we introduce a new technique for estimating the attenuation coefficient. The effect of attenuation on an interrogating signal with a gaussian-shaped spectrum can be obtained by studying the Wigner distribution of reflected rf data based on a one-dimensional signal model. We show that under the condition that the attenuation varies linearly with frequency, the spectral mean of the reflected signal decreases linearly with time. The estimation algorithm models the pulse-echo signal as the output of a second-order time-varying state-space innovations model driven by white noise. The state coupling matrix A and the output coupling vector C vary with time in a known fashion; moreover, they are also functions of an unknown constant parameter theta. The attenuation coefficient, which is one of the elements of theta, can be estimated directly using a recursive system identification algorithm. The algorithm was verified using both computer-generated synthetic data and in-vivo liver data of known diagnosis. The results show correlation between the estimated parameter and the pathological state of the tissue.

Algorithms↗
PubMed2004

Bias and uncertainty in heart rate variability spectral indices due to the finite ECG sampling frequency.

Spectral analysis of the heart rate variability is becoming a usual tool as a marker of the autonomic nervous system. The final output of the spectral analysis is a set of indices that are always estimators due to technical limitations. In this work, the bias and the uncertainty in the VLF, LF, HF and LF/HF indices due to the finite sampling frequency of the ECG are analysed. The results indicate that for low sampling frequency (125 Hz), the bias and uncertainty in the HF and LF/HF indices can blur the results of the analysis, especially if the RR time series has low variability. The HF index is overestimated and, accordingly, the LF/HF index is underestimated. Then, results from RR time series with low sampling frequency must be used with care. The uncertainty of the spectral indices is proportional to the inverse of the sampling frequency and the bias is proportional to the inverse of the square sampling frequency.

Electrocardiography↗
PubMed1998

Molecular genetics of spectral tuning in New World monkey color vision.

Although most New World monkeys have only one X-linked photopigment locus, many species have three polymorphic alleles at the locus. The three alleles in the squirrel monkey and capuchin have spectral peaks near 562, 550, and 535 nm, respectively, and the three alleles in the marmoset and tamarin have spectral peaks near 562, 556, and 543 nm, respectively. To determine the amino acids responsible for the spectral sensitivity differences among these pigment variants, we sequenced all exons of the three alleles in each of these four species. From the deduced amino acid sequences and the spectral peak information and from previous studies of the spectral tuning of X-linked pigments in humans and New World monkeys, we estimated that the Ala --> Ser, Ile --> Phe, Gly --> Ser, Phe --> Tyr, and Ala --> Tyr substitutions at residue positions 180, 229, 233, 277, and 285, respectively, cause spectral shifts of about 5, -2, -1, 8, and 15 nm. On the other hand, the substitutions His --> Tyr, Met --> Val or Leu, and Ala --> Tyr at positions 116, 275, and 276, respectively, have no discernible spectral tuning effect, though residues 275 and 276 are inside the transmembrane domains. Many substitutions between Val and Ile or between Val and Ala have occurred in the transmembrane domains among the New World monkey pigment variants but apparently have no effect on spectral tuning. Our study suggests that, in addition to amino acid changes involving a hydroxyl group, large changes in residue size can also cause a spectral shift in a visual pigment.

Amino Acid Substitution↗
PubMed1998

Spectral bandwidths for the detection of color.

The spectral properties of human color detection mechanisms were measured using a noise masking technique that minimizes the possibility of off-axis looking and artifactually narrow estimates of bandwidth. Observers were induced to use a single detection mechanism throughout a spectral bandwidth measurement by using sectored noise to mask a time-varying signal of fixed chromatic properties. Sectored noise draws samples from sectors of variable width in the color plane, centered on the signal axis. Contrast thresholds for equiluminant signals that appeared yellow, orange, red and violet were found to depend on the power of the noise, projected along the chromatic axis of the signal, but not on the sector width of the noise. These results are consistent with the activity of spectrally broadband, linear detection mechanisms that are tuned to the signal color directions tested.

Color Perception↗