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Results for “Equilibrium optimization”

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At least 361 records · Page 20Linked to original sources
PubMed1990

Optimal interpretation of the supine exercise electrocardiogram in patients with right bundle branch block.

A detailed analysis of the exercise ECG was performed in 82 patients with right bundle branch block who underwent supine exercise equilibrium radionuclide angiography. The sensitivity and specificity of each individual electrocardiographic lead for the detection of a positive radionuclide angiogram was determined. Leads V5 and V6 had a sensitivity of 58 percent and a specificity of 89 percent. The limb leads and lead V4 had a lower sensitivity, but an equivalent specificity. Leads V1 and V3 each had a clearly lower specificity that ranged from 56 to 67 percent. Receiver operating characteristic curve analysis demonstrated that the optimal interpretation of the exercise ECG included the limb leads and V4 to V6, but not V1 to V3. The results of coronary angiography in the subset of 16 patients who underwent this procedure confirmed these findings.

Bundle-Branch Block↗
PubMed1976

Control of the RIA method as viewed from the standpoint of the investigation on the kinetics of the insulin-125 I-antibody reaction.

In this paper attempts were made towards the optimalization and the control of some parameters of the RIA reaction. Basing on the law mass action, as well as on the Scatchard's and Sip's equations, the equilibrium constants for the reversible reaction: insulin-125I-antibody for different incubation temperatures were calculated. Moreover a characteristic of the antiinsulin antibody by means of the "alpha"heterogeneity coefficient was done, as well as the values of the thermodynamic function increments were calculated, which made possible to point out explicitly the optimal shape of the standard curve.

Insulin Antibodies↗
PubMed2002

Evolutionary affinity and selectivity optimization of a pesticide-selective antibody utlizing a hapten-selective immunoglobulin repertoire.

Selectivity and sensitivity are considered as pivotal criteria for the quality of immunochemical assay designs in environmental analysis. They are essentially determined by the variable domains of the implemented antibody. The variable domains of a triazine-selective single-chain Fv (scFv) were genetically engineered by stringent molecular evolution in order to optimize analytical characteristics of the corresponding atrazine immunoassay. Gene variation of the template antibody by sequential shuffling against the variable heavy and light chain repertoire of a triazine-selective immunoglobulin library was enhanced by introducing additional point mutatons. Improved scFv variants were selected by phage display employing an atrazine derivative. By this means the paramounting affinity of the initial scFv to sebuthylazine was shifted for the mutant antibodies toward a preferential recognition of the envisaged target analyte atrazine. In addition, the detection limit of the atrazine assaywas significantly improved by factor 25 from 5.1 microg/L for the initial template antibody to 0.2 microg/L for the mutant antibodies. The contribution of the engineered antibody variants to the assay improvement is also reflected by a shift of the equilibrium dissociation constant KD from 1.27 x 10(-8) M of the template antibody to 7.46 x 10(-10) M of the optimized variant. Sequence analysis revealed a bias of amino acid substitutions in the first two complementarity-determining regions (CDR) and the flanking framework regions of both variable chains for the shuffled clones as well as a deletion in the CDR3 of the light chain. Particularly the mutations of the VL domain turned out to have a decisive impact on the alterations in the analytical performance of the engineered scFv mutants. The application of the mutant antibodies for the atrazine determination of soil samples revealed consistency with HPLC data within the experimental error.

Animals↗
PubMed2000

Measurement of rubidium and xenon absolute polarization at high temperatures as a means of improved production of hyperpolarized (129)Xe.

We report on a rubidium-xenon (Rb-Xe) polarization unit for the continuous production of large quantities of hyperpolarized (129)Xe. The unit includes two diagnostic systems which enable the absolute measurement of both the (85)Rb and (129)Xe polarization in situ and at high temperatures. The Rb diagnostic system allows the measurement of one- or two-dimensional images of the absolute Rb polarization and thus enables the experimental study of light penetration into the optical pumping cell. The equilibrium Xe polarization measured in the optical pumping cell and in the freezing unit is typically approximately 20%, under optimal flowing conditions, and this is much lower than the volume-averaged rubidium polarization.

Isotope Labeling↗
PubMed2003

Fast measurement of relaxation times by steady-state free precession of 129Xe in carrier agents for hyperpolarized noble gases.

Hyperpolarized gases ((129)Xe and (3)He) are being used increasingly in both MRI and NMR spectroscopy studies. However, it has been shown that carrier agents are required to preserve the long relaxation times of gases in biological fluids. Optimized gas transport can be achieved through controlled T(1) and T(2) measurements of (129)Xe gas at equilibrium, using the steady-state free precession method (SSFP). The accuracy of the method was proven with the use of CuSO(4)-doped water samples and xenon dissolved in chloroform. The following T(1) and T(2) values were measured for xenon dissolved in a 30% intralipid emulsion: T(1) = 29 +/- 3 s; T(2) = 1.0 +/- 0.1 s. The values obtained in the intralipid emulsion contrast significantly with those obtained in conventional gas NMR experiments, in which it is commonly assumed that T(1) = T(2). This highlights the importance of obtaining accurate relaxation time measurements for medical applications of hyperpolarized gases.

Drug Carriers↗
PubMed1998

Role of Mg2+ in nucleoside diphosphate kinase autophosphorylation.

Nucleoside diphosphate (NDP) kinase is a ubiquitous enzyme that has been described to have regulatory functions. In addition to its classical enzymatic activity, NDP kinases have been characterized as inhibitors of metastasis, as a factor stimulating gene transcription, and as a protein kinase. In this report we show some characteristics of the autophosphorylation of homogeneous NDP kinase and make a comparison with that of other proteins in crude extracts. By using labeled substrates and fluorescence quenching analysis, we prove that Mg2+ is indeed necessary for the two steps of the ping-pong reaction to take place and present evidence that NTPs or NDPs, when uncomplexed to divalent cations, may not bind the active site in a comparable way to NTP . Mg2+ and NDP . Mg2+. However, even extremely small concentrations of Mg2+ suffice for maximal autophosphorylation which is obtained with Mg2+ in the nanomolar range and 100 microM ATP using homogeneous enzyme. Moreover, lower autophosphorylation levels were observed with increasing concentrations of Mg2+. The autophosphorylation equilibrium varied from 0.19 to 1.6 upon the inclusion of 10 mM EDTA to produce low Mg2+ concentrations. Under optimal conditions (low Mg2+ concentrations and short incubation times) NDP kinase was the only protein phosphorylated in crude extracts from Candida albicans, indicating that the autophosphorylation properties of the enzyme are very singular.

Adenosine Diphosphate↗
PubMed1994

Crystallization and preliminary crystallographic analysis of sfericase. A Bacillus sphaericus calcium-dependent serine proteinase.

Sfericase is an important intracellular proteinase produced by Bacillus sphaericus in the stationary phase of growth. It is a Ca(2+)-dependent serine proteinase with optimal activity at pH 9.0 to 9.3. The molecular mass of sfericase is 32 kDa, as determined by sedimentation equilibrium. It seems to be involved in the interplay of various elements of the mosquitocidal activity of B. sphaericus, and hence is important for biological mosquito control. Sfericase significantly reduces viscosity of human pathological bronchial secretions and has recently shown good clinical effects in treatment of bronchitis, pneumonia and sinusitis. This enzyme was isolated from B. sphaericus and single crystals were obtained by the hanging drop vapor diffusion method. The crystals belong to the monoclinic space group P2, with cell dimensions of a = 46.94 A, b = 64.55 A, c = 86.23 A and beta = 95.4 degrees. These crystals are mechanically strong, they are stable in the X-ray beam and they diffract to better than 1.8 A resolution. The cell dimensions are consistent with four molecules per unit cell and two molecules in the asymmetric unit. A complete native data set to 1.77 A resolution has been collected on a Rigaku R-AXIS-IIc Imaging Plate Detector system and a heavy-atom derivative search is presently in progress.

Amino Acid Sequence↗
PubMed2002

Enhancing bowel adaptation in short bowel syndrome.

Malabsorption of both nonessential and essential nutrients, fluid, and electrolytes will, if not compensated for by increased intake, lead to diminished body stores and to subclinical and eventually clinical deficiencies. By definition, intestinal failure prevails when parenteral support is necessary to maintain nutritional equilibrium. After intestinal resection, adaptation, a progressive recovery from the malabsorptive disorder, may be seen. Research has focused on optimizing remnant intestinal function through dietary or pharmacologic interventions. In this review, factors responsible for the morphologic and functional changes in the adaptive processes are described. Results of clinical trials employing either growth hormone and glutamine or glucagon-like peptide-2 in short bowel patients are presented.

Adaptation, Physiological↗
PubMed1990

A rapid and sensitive ELISA for rainbow trout maturational gonadotropin (tGtH II): validation on biological samples; in vivo and in vitro responses to GnRH.

A rapid and sensitive heterologous enzyme-linked immunosorbent assay (ELISA) was developed to measure rainbow trout maturational gonadotropin. Purified salmon maturational gonadotropin (sGtH II) was used as reference hormone. Optimization of the procedure was performed by using an anti-beta sGtH serum. Two procedures were developed: an equilibrium assay (which did not involve a preincubation step) which lasted for 8 hr and a nonequilibrium assay (which involved a preincubation step) which lasted for 26 hr. The nonequilibrium assay gave the best sensitivity (70 pg/ml sample). GtH II measurements on in vivo and in vitro samples from GnRH analogs or sGnRH experiments showed that the ELISA procedure could be used over a wide range of concentrations. The method was validated by comparing GtH II concentrations measured by both RIA and ELISA.

Animals↗
PubMed2000

Effect of optimization criterion on spinal force estimates during asymmetric lifting.

Optimization-based muscle force prediction models of the lumbar region are used in research and ergonomic practice, usually as a subroutine of a job analysis software package. Various optimization criteria have been put forward for use in rationally selecting a set of muscle forces to satisfy moment equilibrium, including the sum of cubed muscle contraction intensities and a double linear programming procedure for minimizing the spinal compression force and maximum muscle contraction intensity. A laboratory study was conducted to determine whether these two model formulations produce significantly different estimates of spinal forces for a dynamic asymmetric lift. Although statistically significant differences were found between the predictions of the two models, the difference in peak spinal compression force was only 1.1%.

Adult↗
PubMed2001

Effects of sulfur impregnation temperature on the properties and mercury adsorption capacities of activated carbon fibers (ACFs).

Laboratory studies were conducted to determine the role of sulfur functional groups and micropore surface area of carbon-based adsorbents on the adsorption of Hg0 from simulated coal combustion flue gases. In this study, raw activated carbon fibers that are microporous (ACF-20) were impregnated with elemental sulfur between 250 and 650 degrees C. The resulting samples were saturated with respect to sulfur content. Total sulfur content of the sulfur impregnated ACF samples decreased with increasing impregnation temperatures from 250 and 500 degrees C and then remained constant to 650 degrees C. Results from sulfur K-edge X-ray absorption near-edge structure (S-XANES) spectroscopy showed that sulfur impregnated on the ACF samples was in both elemental and organic forms. As sulfur impregnation temperature increased, however, the relative amounts of elemental sulfur decreased with a concomitant increase in the amount of organic sulfur. Thermal analyses and mass spectrometry revealed that sulfur functional groups formed at higher impregnation temperatures were more thermally stable. In general, sulfur impregnation decreased surface area and increased equilibrium Hg0 adsorption capacity when compared to the raw ACF sample. The ACF sample treated with sulfur at 400 degrees C had a surface area of only 94 m2/g compared to the raw ACF sample's surface area of 1971 m2/g, but at least 86% of this sample's surface area existed as micropores and it had the largest equilibrium Hg0 adsorption capacities (2211-11,343 micrograms/g). Such a result indicates that 400 degrees C is potentially an optimal sulfur impregnation temperature for this ACF. Sulfur impregnated on the ACF that was treated at 400 degrees C was in both elemental and organic forms. Thermal analyses and CS2 extraction tests suggested that elemental sulfur was the main form of sulfur affecting the Hg0 adsorption capacity. These findings indicate that both the presence of elemental sulfur on the adsorbent and a microporous structure are important properties for improving the performance of carbon-based adsorbents for the removal of Hg0 from coal combustion flue gases.

Adsorption↗
PubMed1992

A model of the volumetrically-controlled hemodialysis circuit.

We developed a model that predicts the hemodynamics of the volumetrically-controlled circuit used to administer high flux hemodialysis. The equations simulate the entire blood side of the circuit so that blood and dialysate pressures can be predicted from a knowledge of circuit component and patient characteristics. An alternative method of computation has also been devised which permits measured circuit pressures to be used to predict patient blood access pressure, dialyzer resistance to flow and membrane hydraulic conductivity. Success of the model was evaluated by measuring both circuit pressure and component characteristics. The model successfully predicted circuit pressures when measured component characteristics were employed as model inputs. Conversely, the model accurately predicted circuit component characteristics when measured pressures were employed as inputs (8 patients, 30 dialyses). Specific predictions of the model include the following. Elevations of patient blood access pressure will cause blood and dialysate pressures to rise equivalently without affecting the rate of back-filtration or location of pressure equilibrium along the dialyzer axis. Elevated hematocrit is predicted to increase circuit pressures to a degree that is similar to a poorly functioning blood access, however, high hematocrit markedly augments back-filtration and moves the point of pressure equilibrium toward the dialyzer entrance. We conclude that the model provides a predictive tool that can be used to optimize circuit design. Alternatively, the model can be used to separate the influence of a poorly functioning patient access from other factors which can elevate circuit pressures.

Blood Flow Velocity↗
PubMed1999

Molecular chlorine generated by the myeloperoxidase-hydrogen peroxide-chloride system of phagocytes produces 5-chlorocytosine in bacterial RNA.

Myeloperoxidase, a heme enzyme secreted by activated phagocytes, uses H(2)O(2) and Cl(-) to generate the chlorinating intermediate hypochlorous acid (HOCl). This potent cytotoxic oxidant plays a critical role in host defenses against invading pathogens. In this study, we explore the possibility that myeloperoxidase-derived HOCl might oxidize nucleic acids. When we exposed 2'-deoxycytidine to the myeloperoxidase-H(2)O(2)-Cl(-) system, we obtained a single major product that was identified as 5-chloro-2'-deoxycytidine using mass spectrometry, high performance liquid chromatography, UV-visible spectroscopy, and NMR spectroscopy. 5-Chloro-2'-deoxycytidine production by myeloperoxidase required H(2)O(2) and Cl(-), suggesting that HOCl is an intermediate in the reaction. However, reagent HOCl failed to generate 5-chloro-2'-deoxycytidine in the absence of Cl(-). Moreover, chlorination of 2'-deoxycytidine was optimal under acidic conditions in the presence of Cl(-). These results implicate molecular chlorine (Cl(2)), which is in equilibrium with HOCl through a reaction requiring Cl(-) and H(+), in the generation of 5-chloro-2'-deoxycytidine. Activated human neutrophils were able to generate 5-chloro-2'-deoxycytidine. Cellular chlorination was blocked by catalase and heme poisons, consistent with a myeloperoxidase-catalyzed reaction. The myeloperoxidase-H(2)O(2)-Cl(-) system generated similar levels of 5-chlorocytosine in RNA and DNA in vitro. In striking contrast, only cell-associated RNA acquired detectable levels of 5-chlorocytosine when intact Escherichia coli was exposed to the myeloperoxidase system. This observation suggests that oxidizing intermediates generated by myeloperoxidase selectively target intracellular RNA for chlorination. Collectively, these results indicate that Cl(2) derived from HOCl generates 5-chloro-2'-deoxycytidine during the myeloperoxidase-catalyzed oxidation of 2'-deoxycytidine. Phagocytic generation of Cl(2) therefore may constitute one mechanism for oxidizing nucleic acids at sites of inflammation.

Chlorides↗
PubMed1999

A model of the kinetics and dynamics of induction of anaesthesia in sheep: variable estimation for thiopental and comparison with propofol.

We describe a six-compartment kinetic and dynamic physiological model of induction of anaesthesia with thiopental. The model included an accurate account of initial drug distribution by representing the inter-relationships between initial vascular mixing, lung kinetics and cardiac output, and the use of the brain as the target organ for anaesthesia (two-compartment sub-model with slight membrane limitation). It also accounted for thiopental-induced reductions in cerebral blood flow and cardiac output. Parameters for the model were estimated using hybrid modelling from an extensive in vivo data set collected in sheep. Simulations were used to compare the properties of the thiopental model with an analogous previously published model of propofol. Differences in the blood:brain equilibrium half-lives of thiopental (1.22 min) and propofol (4.32 min) contributed to significant differences in the predicted optimal rate of bolus injection of each agent for inducing anaesthesia in sheep.

Anesthesia↗
PubMed1999

Equilibrium and limb coordination in mild cognitive impairment and mild Alzheimer's disease.

OBJECTIVE: To examine changes in equilibrium and limb coordination in normal aging, mild cognitive impairment, and moderate cognitive impairment associated with early probable Alzheimer's disease (AD), by means of parametric clinical measures. DESIGN: Case series SETTING: Out-patient clinic. PARTICIPANTS: A consecutive sample of 365 community-residing ambulatory volunteers (137 men, 228 women; mean age 70.4 +/- 9.4 years; mean educational attainment 14.6 +/- 3.1 years), who were followed in an ongoing longitudinal study of aging and AD, comprising cognitively intact individuals, persons with mild cognitive impairment, and patients with mild AD. MEASUREMENTS: For general magnitude of cognitive function, the Global Deterioration Scale (GDS). For cognition, the Mini-Mental State Examination (MMSE). Equilibrium was assessed with parametric measurements of single leg stance (SLS) and tandem walking (TW). Limb coordination was assessed with parametric measurements of foot tapping (FT), alternating pronation and supination (PS), and sequential finger to thumb tapping (FTH). MAIN RESULTS: After adjustment for age, persons with mild cognitive impairment or mild AD had significantly poorer performance on parametric clinical tests of equilibrium and limb coordination compared with cognitively intact individuals (P < .05). CONCLUSIONS: Changes in equilibrium and limb coordination are clinically demonstrable in persons with mild cognitive impairment and mild AD using simple parametric tests. Such tests could potentially identify individuals with increased risk of falling. Early diagnosis and treatment of conditions that can jeopardize equilibrium and limb coordination, as well as balance and coordination training, might help cognitively impaired older people to maintain optimal function and may decrease the risk of falls and injuries.

Accidental Falls↗
PubMed2001

[Extraction of residual formaldehyde in polymer complex and high performance liquid chromatographic analysis].

This paper presents a simple and accurate method for analyzing formaldehyde in polymer complex by headspace extraction derivatization and HPLC analysis. The sample preparatio of formaldehyde in polymer complex was based on a simple thermodynamic equilibrium in a closed and thermostat jar, and the gaseous formaldehyde in equilibrium could be absorbed and extracted by the liquid in the bottom of the jar. The formaldehyde was derivatized with 2,4-dinitrophenyl hydrazine before chromatography. The influences of temperature, equilibrium time, sample quantity and geometric form on the extraction efficiency were studied. The extraction and HPLC conditions were optimized. The limit of detection (LOD) was 0.1 mg/kg, and the relative standard deviation (RSD) was below 5%, and the recoveries were between 96%-103%. As a result, this method would meet the demands for analyzing microamounts of residual formaldehyde in polymer complex.

Chromatography, High Pressure Liquid↗
PubMed1992

A model for optimal processing of multisensory information in the system for maintaining body orientation in the human.

Considered is the optimal processing of multisensory information to maintain body orientation in the human. It is supposed that the orientation is performed by a system of angular stabilization with only small deviations from the equilibrium believed to be coincided with the local vertical. The linear transformation is determined which minimizes the square loss function for the stabilization error. This transformation comprises two successive steps. One of them is the averaging procedure on the the sensory inputs and the other is the optimal Kalman filtering in time domain. It is shown that the presence of two interacting channels for angular position and angular velocity in the structure of the optimal filter ensures sufficient accuracy of stabilization in both channels for the stabilization system as a whole in spite of the substantial unreliability in transmission in the channel of the angular position.

Cerebellum↗