Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “parameter identification”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,171 records · Page 65Linked to original sources
PubMed1997

Characterization of flavonoids in extracts from four species of Epimedium by micellar electrokinetic capillary chromatography with diode-array detection.

A micellar electrokinetic capillary chromatographic (MEKC) method with diode-array detection is developed for the characterization of pharmacologically active flavonoids in extracts prepared from Epimedium brevicornum, E. humanense, E. coactum, and E. truncatum. The pK(a) values of icarin, epimedin B, and epimedin C are determined by spectrophotometry. Optimal separation of icarin, epimedin B and C, and eight other compounds is achieved by determining pK(a) values and by systematically optimizing electrolytic and instrumental parameters. The repeatability of analyses and the reliability of identification are evaluated by the marker technique. Calculated for relative migration times of flavonoids in the extracts, the repeatability of the analyses varies from 0.7 to 6.4% (nine replicates). For migration indices calculated with two markers, however, the repeatability almost falls below 0.5%. The distribution of the flavonoids is found to differ both qualitatively and quantitatively among the four species. The MEKC technique appears to provide a powerful tool for the identification and quality control of plant drugs and for phytotaxonomic investigations.

Cardiovascular Agents↗
PubMed1996

Experimental antileukocyte interventions in cerebral ischemia.

White blood cells (WBCs) play vital roles in host defense. Recently, increasing interest has been directed toward the question of whether WBCs, particularly polymorphonuclear leukocytes, could also act as mediators of secondary brain damage in the setting of focal and global cerebral ischemia with and without reperfusion. Considerable insight into the importance of WBC-mediated tissue injury has been gained from studies employing antileukocyte interventions in experimental cerebral ischemia. The purpose of this article is to survey the different approaches taken to interfere with WBC inflammatory function. Emphasis is laid on a discussion of the efficacy of these interventions, their effects and side effects on cerebral and systemic parameters, and the power of evidence they provide for identification of WBCs as important factors in cerebral ischemia. The role of WBCs has been investigated in a great variety of global and focal cerebral ischemia models with and without reperfusion, leading to sometimes contradictory results. In the light of currently available data, it seems likely that WBCs contribute to secondary brain damage in the scenario of experimental transient focal cerebral ischemia, if the insult is not too severe.

Adjuvants, Immunologic↗
PubMed2002

Optimization of electromagnetic phased-arrays for hyperthermia via magnetic resonance temperature estimation.

A technique for the optimization of electromagnetic annular phased arrays (APAs) for therapeutic hyperthermia has been developed and implemented. The controllable inputs are the amplitudes and phases of the driving signals of each element of the array. Magnetic resonance imaging (MRI) is used to estimate noninvasively the temperature distribution based on the temperature dependence of the proton resonance frequency (PRF). A parametric model of the dynamics that couple the control inputs to the resultant temperature elevations is developed based on physical considerations. The unknown parameters of this model are estimated during a pretreatment identification phase and can be continuously updated as new measurement data become available. Based on the parametric model, a controller automatically chooses optimal phases and amplitudes of the driving signals of the APA. An advantage of this approach to optimizing the APA is that no a priori information is required, eliminating the need for patient-specific computational modeling and optimization. Additionally, this approach represents a first step toward employing temperature feedback to make the optimization of the APA robust with respect to modeling errors and physiological changes. The ability of the controller to choose therapeutically beneficial driving amplitudes and phases is demonstrated via simulation. Experimental results are presented which demonstrate the ability of the controller to choose optimal phases for the APA using only information from magnetic resonance thermometry (MRT).

Computer Simulation↗
PubMed2007

Spurious counts and spurious results on haematology analysers: a review. Part II: white blood cells, red blood cells, haemoglobin, red cell indices and reticulocytes.

Haematology analysers provide quick and accurate results in most situations. However, spurious results, related either to platelets (part I of this report) or to other parameters from the cell blood count (CBC) may be observed in several instances. Spuriously low white blood cell (WBC) counts may be observed because of agglutination in the presence of ethylenediamine tetra-acetic acid (EDTA). Cryoglobulins, lipids, insufficiently lysed red blood cells (RBC), erythroblasts and platelet aggregates are common situations increasing WBC counts. In most of these instances flagging and/or an abnormal WBC differential scattergram will alert the operator. Several situations lead to abnormal haemoglobin measurement or to abnormal RBC count, including lipids, agglutinins, cryoglobulins and elevated WBC counts. Mean (red) cell volume (MCV) may be also subject to spurious determination, because of agglutinins, excess of glucose or salts and technological considerations. In turn, abnormality related to one measured parameter will lead to abnormal calculated RBC indices: mean cell haemoglobin content (MCHC) is certainly the most important RBC indices to consider, as it is as important as flags generated by the haematology analysers (HA) in alerting the user to a spurious result. In many circumstances, several of the measured parameters from CBC may be altered, and the discovery of a spurious change on one parameter frequently means that the validity of other parameters should be considered. Sensitive flags now allow the identification of several spurious counts, but only the most sophisticated HA have optimal flagging and more simple HA, especially those without a WBC differential scattergram, do not possess the same sensitivity for detecting anomalous results. Reticulocytes are integrated now into the CBC in many HA, and several situations may lead to abnormal counts.

Erythrocyte Count↗
PubMed1997

Closed-loop identification of carotid sinus baroreflex open-loop transfer characteristics in rabbits.

In the circulatory system, a change in blood pressure operates through the baroreflex to alter sympathetic efferent nerve activity, which in turn affects blood pressure. Existence of this closed feedback loop makes it difficult to identify the baroreflex open-loop transfer characteristics by means of conventional frequency domain approaches. Although several investigators have demonstrated the advantages of the time domain approach using parametric models such as the autoregressive moving average model, specification of the model structure critically affects their results. Thus we investigated the applicability of a nonparametric closed-loop identification technique to the carotid sinus baroreflex system by using an exogenous perturbation according to a binary white-noise sequence. To validate the identification method, we compared the transfer functions estimated by the closed-loop identification with those estimated by open-loop identification. The transfer functions determined by the two identification methods did not differ statistically in their fitted parameters. We conclude that exogenous perturbation to the baroreflex system enables us to estimate the open-loop baroreflex transfer characteristics under closed-loop conditions.

Animals↗
PubMed1988

Analysis of metabolic control: new insights using scaled creatine kinase model.

The creatine kinase-adenylate kinase equilibria equations are given a dimensionless form by normalizing to total creatine concentration. Analysis with appropriate equilibrium and cation-binding constants identified two sharply separated phases of energy depletion. In the "buffering" phase, energy is derived from phosphocreatine. In the "depleting" phase, adenine nucleotides are the source of energy. Defining the state of the adenine nucleotide pool requires only pH, phosphocreatine, and creatine concentrations. Analysis of data from skeletal muscle, heart, brain, and smooth muscle demonstrated that the [free adenine nucleotide]/[total creatine] and [total phosphate]/[total creatine] are essentially constant over the greater than 20-fold concentration range among tissues and species. This result permits quantitative evaluation of cell energetics with data scaled to the total phosphate, as obtained with nuclear magnetic resonance studies, or to total creatine, as obtained in chemical analysis of freeze-trapped tissue. By applying the stability of the tissue parameters to the equations, it is demonstrated that unique identification of a hypothesis describing the recruitment of O2 uptake requires testing at several pH values.

Adenine Nucleotides↗
PubMed1997

The growth fraction of normal human epidermis.

In human epidermis, germinative cell production is determined by three parameters: the cell cycle time, the loss of cycling cells by programmed cell death and the proportion of keratinocytes actively engaged in the cell cycle or growth fraction. The last parameter is still a subject of debate as the identification of a proliferative cell with certainty is impossible. Two indirect methods (grain count dilution of labelled cells and continuous labelling) suggest that non-proliferative cells may exist in the germinative compartment of human epidermis. Results obtained in vitro demonstrate that keratinocytes can be blocked in certain conditions in a state of quiescence similar to a G0 phase. Increasing evidence suggests that, as in mouse epidermis, the germinative compartment of human epidermis is and is divided into a small proportion of stem cells (10%) with a high proliferative potential, a larger proportion of transit-amplifying cells with a limited proliferative potential (50%) and postmitotic cells committed to undergo terminal differentiation (40%). In this hierarchical arrangement, most of the nonproliferative cells belong to the postmitotic compartment. If this model is correct, the germinative cell population in a quiescent or G0 state is a small proportion of the stem cell compartment and has therefore little influence on the kinetics of normal human epidermis.

Cell Division↗
PubMed2003

Incremental value of ultrasonic tissue characterization (backscatter) in the evaluation of left ventricular myocardial structure and mechanics in essential arterial hypertension.

BACKGROUND: Ultrasonic backscatter parameters were analyzed in hypertensive patients and divided into groups according to both severity of left ventricular hypertrophy (LVH) (group A: no LVH [n=52]; B: mild to moderate LVH [n=55]; and C: severe LVH [n=10]) and left ventricular geometry (normal geometry [n=44]; concentric remodeling [n=8]; concentric hypertrophy [n=25]; and eccentric hypertrophy [n=40]). METHODS AND RESULTS: We studied 117 male, essential hypertensive patients and 19 normotensive, age-matched (40+/-5 years), healthy subjects who served as controls. Ambulatory and office blood pressure measurements were taken and 2-dimensional Doppler echocardiography and ultrasonic myocardial integrated backscatter (IBS) were performed. A group from the hypertensive study population (n=16) was observed after a period of pharmacological antihypertensive treatment to determine the behavior of backscatter parameters in relation to eventual regression of left ventricular mass (LVM). The cyclic variation index (CVIs) of the backscatter signal at the septum level was grouped according to each LVM level and was 29.4+/-9.3 (controls), 15+/-11 (group A), 9.5+/-10 (group B), and -1.5+/-8.6 (group C) (P<0.001). CVI septum values grouped according to left ventricular geometry were 15+/-11 (normal geometry), 12+/-7 (concentric remodeling), 7+/-11 (concentric hypertrophy), and 7.8+/-11 (eccentric hypertrophy) (P<0.01). Follow-up data demonstrate a significant reduction of LVM after therapy, as well as a significant increase in CVIs toward normal values. CONCLUSIONS: Hypertensive patients with higher LVM had the worst prognosis; in fact, those patients had the most significant CVI alterations. Regression of LVM subsequent to chronic pharmacological therapy induces a normalization of ultrasonic backscatter parameters. Ultrasonic tissue characterization (backscatter) analysis could allow early identification of patients at risk of developing complications of hypertensive cardiopathy.

Adult↗
PubMed1994

Genetic information and ecosystem health: arguments for the application of chaos theory to identify boundary conditions for ecosystem management.

To meet the demands for goods and services of an exponentially growing human population, global ecosystems will come under increasing human management. The hallmark of successful ecosystem management will be long-term ecosystem stability. Ecosystems and the genetic information and processes which underlie interactions of organisms with the environment in populations and communities exhibit behaviors which have nonlinear characteristics. Nonlinear mathematical formulations describing deterministic chaos have been used successfully to model such systems in physics, chemistry, economics, physiology, and epidemiology. This approach can be extended to ecotoxicology and can be used to investigate how changes in genetic information determine the behavior of populations and communities. This article seeks to provide the arguments for such an approach and to give initial direction to the search for the boundary conditions within which lies ecosystem stability. The identification of a theoretical framework for ecotoxicology and the parameters which drive the underlying model is a critical component in the formulation of a prioritized research agenda and appropriate ecosystem management policy and regulation.

Ecosystem↗
PubMed2006

The fragile breakage versus random breakage models of chromosome evolution.

For many years, studies of chromosome evolution were dominated by the random breakage theory, which implies that there are no rearrangement hot spots in the human genome. In 2003, Pevzner and Tesler argued against the random breakage model and proposed an alternative "fragile breakage" model of chromosome evolution. In 2004, Sankoff and Trinh argued against the fragile breakage model and raised doubts that Pevzner and Tesler provided any evidence of rearrangement hot spots. We investigate whether Sankoff and Trinh indeed revealed a flaw in the arguments of Pevzner and Tesler. We show that Sankoff and Trinh's synteny block identification algorithm makes erroneous identifications even in small toy examples and that their parameters do not reflect the realities of the comparative genomic architecture of human and mouse. We further argue that if Sankoff and Trinh had fixed these problems, their arguments in support of the random breakage model would disappear. Finally, we study the link between rearrangements and regulatory regions and argue that long regulatory regions and inhomogeneity of gene distribution in mammalian genomes may be responsible for the breakpoint reuse phenomenon.

Algorithms↗
PubMed1989

Applied physiology of cross-country skiing.

Cross-country ski racing has evolved rapidly in recent years. Of particular interest has been the development and proliferation of the faster freestyle or skating techniques. In spite of changes in technique and equipment, the fact that elite cross-country ski racers have some of the highest aerobic power values reported for endurance athletes has not changed. Successful ski racers have higher percentages of slow twitch muscle fibres and higher anaerobic thresholds, but lower anaerobic power scores than Alpine skiers. Cross-country skiers are also lean, as are distance runners. The absolute bodyweight of the ski racer, however, is much more variable than that of distance runners. Since light skiers will have an advantage on steep uphill courses and heavier skiers will be favoured by level, downhill, and less steep uphill courses, the variability of courses available in international competition explains why successful skiers are so variable with respect to bodyweight. The physiological characteristics of the elite skier are a result of both genetics and adaptation to rigorous multiyear, year-round training programmes. Identification of systematic procedures for specifically challenging the physiological parameters which are requisite for ski racing are being examined. Investigation of ventilatory and lactate thresholds as well as heart rate as parameters for quantifying training intensity is of particular interest at this time.

Humans↗
PubMed2003

9-hydroxyellipticine and derivatives as chemotherapy agents.

The hydroxy group in 9-hydroxyellipticines increases the apparent affinity for DNA, stabilisation of toposiomerase II-DNA cleavable complex, oxidation to reactive quinone-imine intermediates, phosphorylation of p53 suppressor proteins and cytotoxicity relative to the parent ellipticines. Recent studies have focused on the mechanism of inhibition of phosphorylation of the mutant type of p53 protein, structural characterisation of the drug-DNA complex, the synthesis of carbohydrate derivatives and calculations of physical parameters, including dipole moments, as potential screens to allow identification of new active derivatives. Derivatisation at the 2- and 9-positions has lead to significant improvements in the in vivo activity of the 9-hydroxyellipticine derivatives and has provided important insights into the mechanism of action of these compounds.

Animals↗
PubMed2001

Metabolism profiling, and cytochrome P450 inhibition & induction in drug discovery.

To reduce the high attrition rates of NCEs in preclinical and clinical development uncovering pharmacokinetics, toxicokinetics, drug metabolism, and drug-drug interactions early in drug discovery would be highly valuable. There have been many in vitro screens developed for these areas that have higher sample throughput, which is consistent with the iterative cycle of a typical drug discovery research project. We have presented the present status and given detailed descriptions of biotransformation, metabolic stability assays, identification of drug metabolizing P450 enzymes, prediction of pharmacokinetic parameters from in vitro metabolism data, structure elucidation of metabolites, CYP450 inhibition assays and CYP450 induction assays from a drug discovery perspective. Strategies for the proper sequencing of primary and secondary assays employedfor drug metabolism and CYP450 inhibition & induction is discussed.

Animals↗
PubMed2001

A mathematical model of the fetal cardiovascular system based on genetic algorithms as identification technique.

The development of fetal cardiac surgery, considered the ultimate goal in the treatment of congenital cardiac malformations, needs to be supported by detailed knowledge of the blood circulation in the fetal cardiovascular system. The hemodynamic behavior in distal territories is usually inferred from vessel resistance indices, which give limited physiological information. This study presents a mathematical model of the human fetal global cardiovascular system, developed to clarify the relationships and differences existing between upper and lower body circulation. We modelled the heart with two time-varying capacitances, each representing the respective ventricle's pressure-volume relationship. The fetal vascular system was represented using two six-element Windkessel models, for the upper and lower body respectively. We obtained the identification of the set of circuital and elastance function parameters of the model using Genetic Algorithms (GAs), which follow the laws of evolutionary theory. We compared the results of our numerical study on the model identified with data collected from measurements and literature, to validate the proposed global cardiovascular system model of the human fetus. This model is intended as an instrument to investigate the differences in blood distribution between the different vascular districts in the upper and lower fetal body and the role of the aortic isthmus, the small tract of vessel connecting upper and lower fetal vascular beds; it may also represent a useful tool in the assessment of dynamic balance during mechanical assistance of circulation.

Algorithms↗
PubMed2004

Patients who talk and deteriorate: a new look at an old problem.

BACKGROUND AND METHODS: We sought to review established prognostic indicators applied to Asian population, and to identify new risk factors for deterioration in patients who talked and deteriorated after traumatic brain injury (TBI). This retrospective study used our prospectively maintained TBI database. From August 1999 to July 2001, 324 patients were admitted to the neurosurgical intensive care unit (ICU). Thirty-eight patients (11.8%) talked between injury and subsequent deterioration into coma. Independent outcome predictors were studied. RESULTS AND CONCLUSION: Fourteen patients had subdural haematomas, 9 extradural haematomas, 19 contusions/haematomas and 3 subarachnoid haemorrhages. 81.5% of the patients had mass lesions potentially requiring surgery. Twenty patients had good functional recovery at 6 months (Glasgow Outcome Score 4 and 5); 18 were dead or vegetative. Age, gender, type of intracranial lesion and presence of coagulopathy were significantly correlated with outcome. Intracranial haematomas continue to be most significant in patients who talk and deteriorate. Coagulopathy was the strongest prognostic predictor of poor outcome with fibrinolytic parameters being reliable prognostic markers of head injury. Early identification, continued monitoring and treatment of coagulopathy should be our new look at improving outcome of these patients.

Adolescent↗
PubMed2001

[Optimization of the conditions for RAPD-PCR of Candida spp. and Cryptococcus spp].

In this study, we determined the optimal RAPD amplification conditions to obtain genetic molecular markers for the rapid and accurate identification of Cryptococcus spp. and Candida spp. The following parameters are modified: template DNA, DNA polymerase, magnesium cloride and primer concentration; denaturation, annealing and extension time, temperature of annealing and thermal cycles. After the optimization, reliable and reproducible RAPD patterns are obtained.

English Abstract↗
PubMed1990

Quantitative morphological study of Langerhans cells by computerized image analysis.

ATPase-stained normal and topical nitrogen mustard treated Langerhans cells (LC) in guinea pig epidermis were studied quantitatively and morphologically by computerized image analysis. Significant correlation and linear regression were found between the perimeter and square root of its area for both cytoplasm and nucleus; a theoretical basis was thus given for morphological identification of LC. The directly measured and derived geometric parameters indicated not only substantial alteration of cytoplasm morphology of post-treated LC such as cytoplasmatosis and dendrites reduction but also a potential change of nuclear size and functional status. We conclude that quantitative morphological analysis is an objective, precise and practical method for LC research.

Animals↗
PubMed1985

Cancer risk factors in human studies.

The historical developments leading to the acceptance of the influence of dietary and behavioral aspects of our life-style on cancer are reviewed. However, present information is usually insufficient to permit description of the complex mechanisms involved that are unlikely to yield to classical epidemiologic approaches alone. Better integrated laboratory epidemiologic studies are required that use more advanced nonintervention techniques. Progress may be slow in the identification of such factors in view of the many parameters involved, the absence of a single predominant or avoidable cause in many cancers, and the lack of adequately developed laboratory techniques for epidemiologic application.

Behavior↗