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PubMed2001

Respiratory and cardiovascular adaptations to progressive hypoxia; effect of interval hypoxic training.

AIM: Interval hypoxic training was proposed as a technique for adapting hypoxia of various origins. Its effects on the hypoxic ventilatory response and on cardiovascular autonomic control are unknown. METHODS AND RESULTS: We recorded ventilation, end-tidal oxygen (PETO2) and carbon dioxide partial pressures, RR interval and blood pressure during progressive isocapnic hypoxia, before and after 14 days of: (a) interval hypoxic training (three to four periods of 7 min progressive hypoxia in 1 h, each day) in 12 healthy men (training group); (b) breathing into a spirometer by six age-matched male controls. The hypoxic ventilatory response was estimated by the hyperbolic relationship between PETO2 and ventilation (shape factor A). Spectral analysis was used to characterize low- (mainly sympathetic) and high-frequency (vagal) cardiovascular fluctuations. Shape factor A was increased in the interval hypoxic training group from 268+/-59 to 984+/-196 l x mmHg(-1)(P<0.003), but not in the control group (from 525+/-180 to 808+/-245 l x mmHg(-1), P=ns). Before interval hypoxic training, progressive hypoxia decreased, to a similar extent in both groups, mean RR, RR variability and high-frequency power. After interval hypoxic training, RR still decreased significantly, but the decrease in RR variability and high-frequency power was no longer significant in the training group. No significant changes were observed in blood pressure fluctuations. No changes were observed in the control group. CONCLUSIONS: Two weeks of interval hypoxic training increased the hypoxic ventilatory response, in association with reduced vagal withdrawal during progressive hypoxia.

Adult↗
PubMed2004

Flow motion in the intestinal villi during hemorrhagic shock: a new method to characterize the microcirculatory changes.

Conventional parameters are often inadequate to describe the dynamic flow changes in microcirculation. We used a novel approach to characterize oscillatory flow conditions in a canine model of hemorrhagic shock. Microcirculation in the ileal mucosal villi was visualized using intravital microscopy with the orthogonal polarization spectral imaging technique. The distribution of red blood cell velocity (RBCV) was estimated from the relative time periods of observed RBCV, and the average RBCV (A-RBCV) and its SD were then computed from the first and second moments of the RBCV distribution, respectively. Hemorrhagic shock (for 60 min) was followed by resuscitation with saline, hypertonic saline-Dextran solution (HSD, 7.2% NaCl-10% Dextran, 4 mL/kg), or HSD supplemented with the selective endothelin-A receptor antagonist ETR-p1/fl peptide (100 nmol/kg), respectively. The macrohemodynamic derangement (70% decrease in cardiac index and ileal blood flow) during shock was associated with the appearance of flow motion in the villi and an enhanced endothelin-1 release. The calculated A-RBCV was decreased by 40%. At resuscitation onset, continuous flow periods were transiently seen in 33%, 40%, and 50% of the experiments after saline, HSD, and HSD + ETR p1/fl treatment, respectively. HSD with or without endothelin-A antagonist treatment resulted in an increased relative duration of high-flow periods (by 20%) and a significant, 20% to 40% rise in A-RBCV. These results demonstrate that time-wise variability of RBCV should be used for the analysis of oscillatory flow conditions. The probabilistic estimation of A-RBCV provides a quantitative basis for comparison of the effectiveness of different resuscitation or vasoactive strategies.

Animals↗
PubMed2004

Wideband reflectance measures of the ipsilateral acoustic stapedius reflex threshold.

OBJECTIVE: The purpose of this study was to develop a method for acoustically measuring the ipsilateral acoustic stapedius reflex threshold by using wideband shifts in energy reflectance and admittance. DESIGN: A group of 27 young adult subjects with normal hearing participated in the study. Contralateral reflex thresholds were first measured for a 4000 Hz activator tone (maximum level, 92 dB SPL), using a clinical method with a 226 Hz probe tone. Ipsilateral and contralateral reflex thresholds were then measured by using an experimental wideband reflectance and admittance system that used a band-filtered click (200 to 2000 Hz) as the probe stimulus, presented simultaneously with the 4000 Hz activator tone. Reflex thresholds for the wideband system were determined by using statistical tests of the magnitude of the reflex responses as well as their correlation with other reflex responses. RESULTS: Clinical and experimental reflex thresholds were obtained for 9 of the 27 subjects for all conditions. Clinical reflex thresholds were absent for 8 subjects for whom experimental reflex thresholds were present and were present for 5 subjects who had absent experimental reflex thresholds for one or more conditions. An additional 5 subjects had absent reflex thresholds in all conditions, consistent with the low maximum level of the activator. Wideband measures of contralateral reflex thresholds were approximately 3 dB lower than those obtained with the clinical system. The magnitudes of the group means of the reflex responses were similar for ipsilateral and contralateral stimulations. CONCLUSIONS: Wideband measures of reflectance and admittance may be used to estimate the ipsilateral acoustic stapedius reflex threshold by separating in frequency the spectral energies of the wideband probe stimulus from the activator stimulus. This technique holds promise for measuring reflex thresholds for individuals with absent reflex thresholds through the use of standard clinical methods.

Acoustic Impedance Tests↗
PubMed1991

Excitatory amino acid receptor-channels in Purkinje cells in thin cerebellar slices.

Glutamate receptors of the N-methyl-D-aspartate (NMDA) and non-NMDA type serve different functions during excitatory synaptic transmission. Although many central neurons bear both types of receptor, the evidence concerning the sensitivity of cerebellar Purkinje cells to NMDA is contradictory. To investigate the receptor types present in Purkinje cells, we have used whole-cell and outside-out patch-clamp methods to record from cells in thin cerebellar slices from young rats. At a holding potential of -70 mV (in nominally Mg(2+)-free medium, with added glycine) NMDA caused a whole-cell current response which consisted of a dramatic increase in the frequency of synaptic currents. In the presence of tetrodotoxin (TTX) and the gamma-aminobutyric acidA (GABAA) receptor antagonist bicuculline, spontaneous synaptic currents and responses to NMDA were inhibited. In a proportion of cells a small polysynaptic response to NMDA persisted, which was further reduced by the non-NMDA receptor antagonist 6-cyano-2,3-dihydro-7-nitroquinoxalinedione (CNQX). The non-NMDA glutamate receptor agonists kainate (KA), quisqualate (QA) and s-alpha-amino-3-hydroxy-5-methyl-4-isoazolepropionic acid (s-AMPA), evoked large inward currents due to the direct activation of receptors in Purkinje cells. NMDA applied to excised membrane patches failed to evoke any single-channel currents, whereas s-AMPA and QA caused small inward currents accompanied by marked increases in current noise. Spectral analysis of the s-AMPA noise in patches gave an estimated mean channel conductance of approximately 4 pS.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Spectral moments of correlated Wishart matrices.

We present an analytic method to determine the spectral properties of the covariance matrices constructed of correlated Wishart random matrices. The method gives, in the limit of large matrices, exact analytic relations between the spectral moments and the eigenvalue densities of the covariance matrices and their estimators. The results can be used in practice to extract the information about genuine correlations from the given experimental realization of random matrices.

Journal Article↗
PubMed2005

Moments of spectral functions: Monte Carlo evaluation and verification.

The subject of the present study is the Monte Carlo path-integral evaluation of the moments of spectral functions. Such moments can be computed by formal differentiation of certain estimating functionals that are infinitely differentiable against time whenever the potential function is arbitrarily smooth. Here, I demonstrate that the numerical differentiation of the estimating functionals can be more successfully implemented by means of pseudospectral methods (e.g., exact differentiation of a Chebyshev polynomial interpolant), which utilize information from the entire interval . The algorithmic detail that leads to robust numerical approximations is the fact that the path-integral action and not the actual estimating functional are interpolated. Although the resulting approximation to the estimating functional is nonlinear, the derivatives can be computed from it in a fast and stable way by contour integration in the complex plane, with the help of the Cauchy integral formula (e.g., by Lyness' method). An interesting aspect of the present development is that Hamburger's conditions for a finite sequence of numbers to be a moment sequence provide the necessary and sufficient criteria for the computed data to be compatible with the existence of an inversion algorithm. Finally, the issue of appearance of the sign problem in the computation of moments, albeit in a milder form than for other quantities, is addressed.

Journal Article↗
PubMed1998

Absolute soft X-ray measurements using an ion chamber.

Measurements of soft X-ray absolute intensities have been carried out using a double ion chamber and monochromated synchrotron radiation. The chamber is cylindrical and 1.3 m long. The soft X-ray beam enters the chamber at a position off the central axis, and the produced ions are collected with electrodes on the opposite side to the photon entrance. An index constant for rare gas, the gamma-value, which is the average number of electrons emitted from an atom having absorbed a photon, was used for obtaining the absolute photon intensity. The obtained intensity ranges from 1 Gphotons s(-1) to 25 Gphotons s(-1) in the energy range 72-800 eV. The estimated uncertainty is about 5-20% depending on the intensity and the spectral purity of the soft X-rays.

Journal Article↗
PubMed1996

Neural correlates of the pitch of complex tones. I. Pitch and pitch salience.

1. The temporal discharge patterns of auditory nerve fibers in Dial-anesthetized cats were studied in response to periodic complex acoustic waveforms that evoke pitches at their fundamental frequencies. Single-formant vowels, amplitude-modulated (AM) and quasi-frequency-modulated tones. AM noise, click trains, and other complex tones were utilized. Distributions of intervals between successive spikes ("1st-order intervals") and between both successive and nonsuccessive spikes ("all-order intervals") were computed from spike trains. Intervals from many fibers were pooled to estimate interspike interval distributions for the entire auditory nerve. Properties of these "pooled interspike interval distributions," such as the positions of interval peaks and their relative heights, were examined for correspondence to the psychophysical data on pitch frequency and pitch salience. 2. For a diverse set of complex stimuli and levels, the most frequent all-order interspike interval present in the pooled distribution corresponded to the pitch heard in psychophysical experiments. Pitch estimates based on pooled interval distributions (30-85 fibers, 100 stimulus presentations per fiber) were highly accurate (within 1%) for harmonic stimuli that produce strong pitches at 60 dB SPL. 3. Although the most frequent intervals in pooled all-order interval distributions were very stable with respect to sound intensity level (40, 60, and 80 dB total SPL), this was not necessarily the case for first-order interval distributions. Because the low pitches of complex tones are largely invariant with respect to level, pitches estimated from all-order interval distributions correspond better to perception. 4. Spectrally diverse stimuli that evoke similar low pitches produce pooled interval distributions with similar most-frequent intervals. This suggests that the pitch equivalence of these different stimuli could result from central auditory processing mechanisms that analyze interspike interval patterns. 5. Complex stimuli that evoke strong or "salient" pitches produce pooled interval distributions with high peak-to-mean ratios. Those stimuli that evoke weak pitches produce pooled interval distributions with low peak-to-mean ratios. 6. Pooled interspike interval distributions for stimuli consisting of low-frequency components generally resembled the short-time auto-correlation function of stimulus waveforms. Pooled interval distributions for stimuli consisting of high-frequency components resembled the short-time autocorrelation function of the waveform envelope. 7. Interval distributions in populations of neurons constitute a general, distributed means of encoding, transmitting, and representing information. Existence of a central processor capable of analyzing these interval patterns could provide a unified explanation for many different aspects of pitch perception.

Acoustic Stimulation↗
PubMed2000

Preferred technique for blood flow volume measurement in cerebrovascular disease.

BACKGROUND AND PURPOSE: A noninvasive reliable technique that can reveal cerebral blood flow volume could be a valuable tool in screening programs for stroke prevention. In diagnostic ultrasonography, spectral Doppler imaging (SDI) is popular among sonologists and vascular technologists to estimate blood flow volume despite its documented inaccuracy and the availability of the more accurate technique of color velocity imaging (CVI). The aim of the present study was to demonstrate the discrepancy of blood flow volume estimation with CVI and SDI with use of an "internal" standard. METHODS: The common, internal, and external carotid arteries of 50 healthy subjects (22 men, 28 women, age range 19 to 54 years) were examined with CVI and SDI. The total blood flow volume of the internal and external carotid arteries was then compared with the ipsilateral common carotid artery flow. An accurate technique would demonstrate no difference. The difference (expressed as a percent inconsistency) was therefore a measure of the accuracy of the method. RESULTS: The mean+/-SD inconsistency was found to be 10.6+/-8.3% for CVI and 27.9+/-14.3% for SDI. The difference in inconsistency between CVI and SDI in measurement of carotid blood flow volume was statistically significant (P<0.01). CONCLUSIONS: CVI is more accurate than SDI in the determination of blood flow volume in the carotid arteries. For noninvasive clinical estimation of cerebrovascular blood flow volume, CVI quantification should be the preferred technique.

Adult↗
PubMed2004

Intensities of calcium dipicolinate and Bacillus subtilis spore Raman spectra excited with 244 nm light.

Ultraviolet (UV) resonance Raman spectra of Bacillus subtilis endospores have been excited at 244 nm. Spectra can be interpreted in terms of contributions from calcium dipicolinate and nucleic acid components. Differences between spectra of spores and vegetative cells are very large and are due to the dominance of the dipicolinate features in the spore spectra. Because the DNA and RNA composition of B. subtilis spores is known and because the cross-sections of Raman bands belonging to DNA and RNA bases are known, it is possible to calculate resonance Raman spectral cross-sections for the spore Raman peaks associated with the nucleic acids. The cross-sections of peaks associated with calcium dipicolinate have been measured from aqueous solutions. Cross-section values of the dominant 1017 cm(-1) calcium dipicolinate peak measured from the Bacillus spores have been shown to be consistent with a calcium dipicolinate composition of ten percent or less by weight in the spores. It is suggested that spectral cross-sections of endospores excited at 244 nm can be estimated to be the sum of the cross-sections of the calcium dipicolinate, DNA, and RNA components of the spore. It appears that the peaks due to DNA and RNA can be used as an internal standard in the calculation of spore Raman peak cross-sections, and potentially the amount of calcium dipicolinate in spores. It is estimated on the basis of known nucleic acid base cross-sections that the most intense Raman band of the Bacillus subtilis spore spectra has a cross-section of no more than 4 x 10(-18) cm(2)/mol-sr.

Bacillus subtilis↗
PubMed1999

[Non-invasive methods of control of the intestinal motility in surgical practice].

Selective spectral peripheric electrogastroenterography (SSPEGEG), the noninvasive method of the gut functional state estimation, is based on registration of biopotentials from the body surface, generated by stomach and intestine, using apparatus-program unit on the PC IBM base. The possibilities and advantages of this method in comparison with others (roentgenological, radiological, radionuclide, balloonographic and tensiographic) were considered. The principles of the SSPEGEG application for clinical monitoring conduction are adduced.

Digestive System↗
PubMed1992

[The central nervous system function of guinea pigs after a prolonged stay in an artificial gaseous environment of varying composition].

The pattern of statistical and correlational-spectral parameters of the heart rate characterising the CNS regulatory functions, was estimated in guinea pigs after their prolonged stay in an artificial gas milieu at the pressure 71 kGs/cm2. The obviousness of activation of subcortical centres was significantly lower after stay in the oxygen-helium-nitrogen mixture than in the oxygen-helium one. The increase of the oxygen partial pressure up to 0.3 kGs/cm2 exerted a favourable effect.

Animals↗
PubMed1992

Identification by site-directed mutagenesis of two lysine residues in cholesterol side chain cleavage cytochrome P450 that are essential for adrenodoxin binding.

Utilizing site-directed mutagenesis and an Escherichia coli expression system for bovine cholesterol side chain cleavage cytochrome P450, lysine residues at 377 and 381 are found to play crucial roles in binding bovine adrenodoxin, required for transfer of electrons to mitochondrial P450s. These lysine residues are conserved among mitochondrial P450s and have been implicated previously by chemical modification studies as being important for adrenodoxin binding. In the present study, site-directed mutagenesis producing either neutral or positive amino acids at 377 or 381 has no effect on the structure of side chain cleavage cytochrome P450 as determined spectrally or on the enzymatic conversion of cholesterol to pregnenolone. However, the estimated Ks of adrenodoxin binding is increased approximately 150-600-fold depending on the particular mutation. Therefore these conserved positively charged residues in mitochondrial P450s are the key sites for adrenodoxin binding which is electrostatic in nature.

Adrenodoxin↗
PubMed2005

[Use of a 3-oxypiridine antioxidant in combined therapy of patients with partial epilepsy].

Fifty-four patients with partial epilepsy (age 18-50 years, 26 males and 28 females, illness duration from 6 months to 18 years) have been examined. Idiopathic epilepsy was diagnosed in 7 patients, symptomatic in 36, cryptogenic in 11. The control group comprised 22 sex- and age-matched individuals. All the patients underwent computerized EEG and pharmaco-EEG testing, MRI or CT of the brain. Follow-up duration was from 6 months to 2.5 years. An antioxidant therapeutic course was conducted during 30 days on the background of the basic anticonvulsive therapy with carbamazepine (finlepsin-retard 200) received in individual dosages. Computer EEG analysis was made using "BRAINWIN" soft (Mitrofanov A.A., "Statokin", Moscow). To estimate the effect of the medications on bioelectric brain activity, methods of spectral and coherent EEG analysis, localization of equivalent dipole source of paroxysmal activity were applied. After a 30-day course of combined therapy with carbamazepine (finlepsin-retard 200) and antioxidant Mexicor, inhibition of generator activity of limbic and hypothalamic as well as stem and cerebellum structures and displacement of generator zones into cortical hemisphere structures were observed that may be explained by enhancement of determinant foci of the cortical structures in inhibition of secondary foci. It may be considered as a favorable prognostic factor, which reduces probability of the secondary generalization of partial epileptic seizures.

Adolescent↗
PubMed1988

[Isolation and properties of myoglobin from murine skeletal muscle].

Myoglobin (Mb) was isolated from skeletal muscle of JCL-ICR mice by heat denaturation-gel filtration combined with ion exchange chromatography or chromatofocusing by which isoelectric point of the main component was estimated as 7.63 +/- 0.09 (20 degrees C). The Mb was homogeneous by gel electrophoretic and ultracentrifugal analysis. The molecular weight by sedimentation equilibrium was 1.80 X 10(4) and essentially identical with the values by the iron analysis (1.82 X 10(4)) and amino acid composition (1.78 X 10(4)) in which one residue of cysteine was found per molecule. The spectroscopic properties of deoxy-, oxy-, carboxy- and ferri-derivatives of the protein were determined in ultraviolet, Soret and visible regions. The pK' of acid-alkaline transition of the ferri-form was estimated as 8.57 +/- 0.30 (30 degrees C) from the pH-dependent spectral changes. The oxygen equilibrium studies revealed complete absence of such allosteric properties as heme-heme interaction, anion effect and Bohr effect. Oxygen tension for the half-oxygenation (P50) was 0.69 +/- 0.06 Torr (20 degrees C) and its temperature-dependent change gave the delta H degrees of -14.1 kcal/mole.

Amino Acids↗
PubMed1979

Sorghum proteinase inhibitors. 2. Mode of interaction with serine proteinases.

Investigations have been carried out on the complex formed between sorghum Inhibitor III and alpha-chymotrypsin by physico-chemical methods. An apparent dissociation constant (Ki) of 4.0 X 10(-8) M has been calculated for the complex. This enzyme-inhibitor complex was isolated by gel filtration on Sephadex G-75 and a molecular weight of 48,000 was estimated for the complex. The formation of the complex was accompanied by spectral changes in the 270--300 nm region of the spectrum. Preliminary evidence suggests that the sorghum Inhibitor III is structurally altered when it is incubated with alpha-chymotrypsin. Catalytically inactive derivative of alpha-chymotrypsin and trypsin, as well as their zymogens, did not interfere with the activity of the sorghum inhibitor towards the native enzymes. Sorghum Inhibitor I was shown to be a 'double-headed' inhibitor since it inhibits both trypsin and alpha-chymotrypsin independently.

Chromatography, Gel↗
PubMed1997

Lumbar paraspinal muscle fatigability in repetitive isoinertial loading: EMG spectral indices, Borg scale and endurance time.

The purpose of this study was to develop a submaximal repetitive isoinertial back muscle endurance test by defining the relationships between the power spectral indices of paraspinal muscle electromyographic (EMG) activities, endurance time and a subjective estimate of fatigue (Borg scale). Bilateral surface EMG recordings were obtained over the lumbar paraspinal muscles in ten individuals who were currently free from back pain. All subjects performed repetitive upper trunk extensions (25 degrees flexion and 5 degrees extension, 30 repetitions per min), while movement below the third lumbar vertebral body was mechanically restricted. The load level depended upon upper body mass, sex, and age. The tests continued for as long as the subjects were able to maintain the required repetition rate (endurance time). Median (MF) and mean power frequency (MPF) slopes were calculated by performing a fast Fourier transformation after confirmation of EMG stationarity by recurrence quantification analysis. MF and MPF correlations with endurance time/Borg scale were measured for the first 60 s (0.60-0.88/0.42-0.86), the first 90 s (0.62-0.89/0.52-0.90), the first 120 s (0.50-0.76/0.41-0.73), and the entire repetitive run (0.63-0.88/0.54-0.90). To test for the reproducibility of the spectral indices EMGs were recorded for 2 min during repetitive loading from the same subjects on two consecutive days. Corresponding spectral slopes of MF and MPF were correlated at 60 s (0.36-0.93), 90 s (0.58-0.92), and 120 s (0.70-0.94) at the L3-L4 and L5-S1 levels, indicating good reproducibility of results from alternate recording sessions at the L5-S1 level. It is concluded that paraspinal muscle spectral indices (MF and MPF) measured before the onset of total muscle fatigue are good predictors of endurance time and are closely related to the subjective perception of fatigue.

Adult↗
PubMed2000

Optical properties of Nannochloropsis sp and their application to remote estimation of cell mass.

The absorption and scattering coefficients and reflectance spectra of ultra-high density Nannochloropsis occulata cultures were investigated in detail to identify the optical properties of the cultures and devise algorithms for remote estimation of dry cell mass in ultra-high cell density cultures. High-spectral resolution measurements of apparent absorption and attenuation as well as reflectance from 400 to 900 nm were carried out in relation to the dry weight, cell count, and pigment concentration in outdoor cultures. Indices calculated as (R(NIR) - R(red))/(R(NIR) + R(red)) and R(NIR)/R(red), in which R(NIR) is reflectance in the range from 750 to 800 nm and R(red) is reflectance in the range 670-680 nm, were used for remote assessment of dry cell mass. Remote estimation in the range 1 to 8 g/L was accomplished with an error of less than 0.66 g/L. A different index, i.e., (R(NIR) - R(red)) was employed for estimation of cell-chlorophyll concentration. This is the first report of in vivo specific absorption coefficient of chlorophyll-a and specific scattering coefficient per dry algal weight of Nannochloropsis sp., providing a basis for remote monitoring of dense phytoplankton masses.

Absorption↗