SEARCH · PubMed Health

Results for “parameter identification”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 649 records · Page 36Linked to original sources

PubMed1998

Viral and host factors in the prediction of response to interferon-alpha therapy in chronic hepatitis C after long-term follow-up.

Acute infection with hepatitis C virus (HCV) develops into a chronic hepatitis in about 50-70% of patients. Treatment of these patients with interferon-alpha (IFN-alpha) results in a sustained long-term response in only 15-20% but causes numerous unwanted side-effects in a higher percentage of patients. The aim of our study was to define host or viral parameters that would allow identification of responders and non-responders to IFN-alpha prior to the onset of treatment. We studied a group of 87 patients suffering from chronic hepatitis C who were treated with IFN-alpha. After long-term follow-up, 18 patients (21%) showed a sustained response to IFN-alpha therapy (normalization of serum transaminases and loss of viral RNA from serum) for up to 7 years after therapy had ceased. By univariate and multivariate analyses, no host factors were found to be predictive of response to therapy. Neither the degree of inflammation or fibrosis in liver biopsy samples obtained before treatment nor immunogenetic factors (major histocompatibility complex II haplotype and tumour necrosis factor-alpha promoter polymorphism) were associated with response to therapy. In contrast, viral parameters showed a strong association with response to therapy. HCV genotype 3 was found significantly more frequently in responders (P = 0.034), and mean HCV RNA concentration was lower in responders (3.1 x 10(4)) than in non-responders (2.5 x 10(5)) (P = 0.01). By multivariate analysis, both HCV genotype and HCV RNA concentration were independent predictors of response to therapy. However, exact prediction of response to treatment for an individual patient was not possible on the basis of pretreatment viral RNA concentration or viral genotype. The best association with response to therapy was found to be clearance of HCV RNA from serum 3 months after the start of treatment (32 of 34 partial and sustained responders vs 0 of 53 non-responders; P = 0.001). In conclusion, determination of pretreatment viral factors, but not host factors, was significantly correlated with treatment response but did not give an accurate prediction for patients, whereas clearance of HCV RNA from serum after 3 months of therapy was predictive of response to therapy.

Adult↗

PubMed2000

Three-dimensional geometric modeling of the cochlea using helico-spiral approximation.

In this paper, the three-dimensional geometry of the human cochlea is modeled by the helico-spiral seashell model. The 3-D helico-spiral model, the generalized representation of the Archimedian spiral model, provides a framework for measuring cochlear features based on consistent estimation of model parameters. Nonlinear least square minimization based algorithms are developed for the identification of rotation, center and intrinsic parameters of the helico-spiral representation. Two algorithms are designed for the rotation axis aligned to the modiolar axis: one is more susceptible in the presence of noise, while the other allows applicability to two-dimensional data sets. The estimated center and intrinsic parameters allow the calculation of length, height and angular positions needed for frequency mapping of multichannel cochlear implant electrodes. Model performance is evaluated with numerically synthesized curves with different levels of added random noise, histologic data and real human cochlear spiral computed tomography data.

Algorithms↗

PubMed2005

Understanding heavy metal and suspended solids relationships in urban stormwater using simulated rainfall.

Urban stormwater from simulated rainfall on three different landuses in Queensland State, Australia (residential, industrial, commercial) was analysed for heavy metals and physico-chemical parameters such as Dissolved Organic Carbon (DOC) and Total Suspended Solids (TSS). Rainfall events were simulated using a specially designed rainfall simulator for paved surfaces. Event mean concentration samples were separated into five different particle sizes and analysed individually for eight metal elements (Zn, Fe, Cr, Cd, Cu, Al, Mn and Pb). Multivariate data analysis was carried out for the data thus generated. It was found that DOC and TSS influence the distribution of the metals in the different particle size classes. Zn was correlated with DOC at all three sites. Similarly, Pb, Fe and Al were correlated with TSS at all sites. The distribution of Cu was found to vary between the three sites, whilst Cd concentrations were too low to assess any relationships with other parameters. No correlation between Electrical Conductivity (EC), pH and heavy metals was found at the three sites. The identification of physico-chemical parameters influencing the distribution process kinetics of heavy metals in urban stormwater will significantly enhance the efficiency of urban stormwater management systems.

Carbon↗

PubMed2006

Stimulus variability and the phonetic relevance hypothesis: effects of variability in speaking style, fundamental frequency, and speaking rate on spoken word identification.

Three experiments were conducted to examine the effects of trial-to-trial variations in speaking style, fundamental frequency, and speaking rate on identification of spoken words. In addition, the experiments investigated whether any effects of stimulus variability would be modulated by phonetic confusability (i.e., lexical difficulty). In Experiment 1, trial-to-trial variations in speaking style reduced the overall identification performance compared with conditions containing no speaking-style variability. In addition, the effects of variability were greater for phonetically confusable words than for phonetically distinct words. In Experiment 2, variations in fundamental frequency were found to have no significant effects on spoken word identification and did not interact with lexical difficulty. In Experiment 3, two different methods for varying speaking rate were found to have equivalent negative effects on spoken word recognition and similar interactions with lexical difficulty. Overall, the findings are consistent with a phonetic-relevance hypothesis, in which accommodating sources of acoustic-phonetic variability that affect phonetically relevant properties of speech signals can impair spoken word identification. In contrast, variability in parameters of the speech signal that do not affect phonetically relevant properties are not expected to affect overall identification performance. Implications of these findings for the nature and development of lexical representations are discussed.

Adolescent↗

PubMed1995

Pharmacokinetics of thiopental after single and multiple intravenous doses in critical care patients.

Thiopental was administered to neurosurgical patients for cerebral protection and its pharmacokinetic parameters were determined after a single bolus of 540, 1000 or 1500 mg (3 subjects) or after multiple doses of 250 mg (5 subjects) and 500 mg (2 subjects) every two hours for up to 7 days. The data were analysed by a two- or three-compartment model and linear kinetics. After a single iv bolus, the mean initial volume of distribution (V1) was 0.481 l.kg-1, and the steady-state volume of distribution (Vss) was 2.16 l.kg-1. The distribution (t1/2 alpha) and elimination (t1/2 beta) half-lives were 0.590 and 5.89 h, respectively, and the mean residence time (MRT) was 7.44 h. The clearance was 5.41 ml.min-1.kg-1. With repeated injections, the pharmacokinetic parameters for each patient were estimated taking into account all administered doses and blood samples, which were taken whenever possible daily at steady state and after the last dose. The variability observed in the pharmacokinetic parameters of thiopental reflected by the coefficient of variation (CV%) was wide but was of similar magnitude within patients (CVintra) as it was between patients (CVinter). The steady-state trough plasma concentration (Cmin obs) ranged from 4.8 to 30 mg.l-1 (mean 16.0 mg.l-1 and median 14.3 mg.l-1). Peak concentrations (Cmax obs) ranged from 8.35 to 45 mg.l-1 (25.4 mg.l-1, and median 23.3 mg.l-1). The values of V1 and Vss were similar to those obtained after a single dose. For V1, the mean was 0.333 l.kg-1. The mean Vss was 2.68 l.kg-1, with a CVintra of 12.6 to 56% and a CVinter of 13.2%. A shorter distribution half-life t1/2 alpha was noted on multiple dosing; the mean value was 0.122 h. The elimination half-life t1/2 beta and the mean residence time became longer due to a decrease in clearance. For t1/2 beta the mean value was 16.3 h. The mean MRT was 21.9 h, CVintra 9.19 to 48.5%, and the CVinter 35.3%. The mean clearance was 2.16 ml.min-1.kg-1, CVintra 7.28 to 25.5%, and the CVinter 20.4%. This value is 50% lower than after a single dose. Identification of the kinetic parameters of thiopental allows simulation of the effects of doses on subsequent plasma levels and will permit a priori prediction of day to day adjustment of drug dosage.

Adolescent↗

PubMed2000

Early predictors of mortality in pneumococcal bacteraemia.

OBJECTIVES: Pneumococcal bacteraemia carries a mortality of about 20%. Approximately 50% of deaths from pneumococcal bacteraemia occur within the first 48 h of admission. In order to influence outcome, critically ill patients should be identified at the time of presentation. This study enables the clinician to rapidly make an evidence-based assessment of a patient's prognosis, allowing the identification of patients who should be placed in a high-risk category at an early stage, when appropriate management is most likely to be effective. METHODS: Data were collected from the medical record of history, physical examination, radiological examination and laboratory investigations done on initial presentation using a standardized proforma. The data were first examined by Pearson's Chi-squared test, with Yates' correction if needed. Variables found to be significantly associated with case fatality ( P < 0.05) by these methods were examined by stepwise logistic regression analysis in order to identify those factors which were independent predictors of case fatality. RESULTS: The overall case fatality was 21%. Older age, apyrexia, tachypnoea, bilateral consolidation, hypoalbuminaemia, elevated aminotransferases, renal impairment, acidosis and leucopaenia were significantly associated with higher case fatality. Older age, acidosis and elevated serum alanine aminotransferase (ALT) were independent predictors of case fatality. Fifty-five percent of isolates belonged to serotypes 4, 6B, 9V, 14, 19F and 23F, to which good antibody levels have been documented in both young and elderly patients post-vaccination. Serotype 14 was most common, and was significantly associated with higher case fatality. Colder weather was associated with a higher incidence of both infection and case fatality. The case fatality amongst patients receiving ITU management was 44%. Less than 50% of patients who died received ITU management. CONCLUSIONS: Despite the increased availability of new antibiotics and vaccines, the mortality of patients with pneumococcal bacteraemia remains unchanged. The parameters above allow early identification of patients with a higher case fatality; these patients may benefit from being placed in a "high-risk" category early on in their management. Vaccination of the elderly may reduce the incidence and/or mortality from pneumococcal bacteraemia. Further studies are required to understand the reasons for referral for intensive therapy in acute pneumococcal bacteraemia and whether ITU management affects outcome.

Acidosis↗

PubMed1975

Lyapunov Redesign of Model Reference Adaptive Control System for long term ventilation of lung.

A lyapunov redesign of Model reference adaptive control system for a long term, automatically regulated, ventilatory system is presented. A fixed resistance-capacitance RC analog lung model is used to generate a desirable (reference response) alveolar pressure. The instantaneous difference in alveolar pressures between the patient and its model is fed to an adaptive controller. The controller is designed to adjust the patient's inflating pressure in such a way as to reduce the instantaneous difference in the alveolar pressures to zero. The adaptive control system described can be implemented provided the patient's alveolar pressure is continuously measurable. Unfortunately, this measurement is impossible to realize; therefore, a method to estimate the continuous alveolar pressure of the patient is to be developed. This estimation is achieved indirectly from the identification process of the patient's respiratory parameter. The same Lyapunov redesign is used in this identification process. Digital simulation of the control of the patient's inflating pressure and the identification process, as well as the simulation of the combined system, were performed. The result has demonstrated the ability of this adaptive system to perform in a fast and stable manner.

Airway Resistance↗

PubMed1992

Ab-initio primitive cell parameters from single convergent-beam electron diffraction patterns: a converse route to the identification of microcrystals with electrons.

A new method for the ab initio derivation of Buerger-reduced primitive cell parameters from coordinate measurements of spots on single convergent-beam electron diffraction (CBED) patterns is described, which does not involve trial-and-error. The pattern can be taken along any zone axis, and misorientations of the crystallite by as much as a few degrees are taken into account without loss of accuracy. This derivation of cell parameters by least-squares analysis of the measurements has been automated in a program called NRCBED. Present accuracy is about 1% on lengths and 2 degrees on angles, but could be significantly improved by modelling projector lens aberrations, or by using a microscope without a projector lens. With present technology, it is possible to obtain a CBED pattern and a semi-quantitative energy-dispersive X-ray (EDX) analysis simultaneously from a single microcrystal a few hundred Angströms across. It becomes therefore possible to identify the material of the crystal on a single CBED pattern: a cell parameter database for known compounds is searched with the primitive cell parameters obtained in the above way, and with a mask describing the EDX results qualitatively. Feasibility is demonstrated on a crystallite of CeO2 500 Angströms across. With this new approach, trial-and-error should disappear from the solution of other long-standing problems: interpretation of X-ray powder patterns for new compounds in the presence of impurity lines, or in the case of multiple phases should become straight-forward.

Cerium↗

PubMed1995

Induction, effects, and quantification of sublethal oxidative stress by hydrogen peroxide on cultured human fibroblasts.

Conditions to induce and parameters to evaluate sublethal oxidative stress of cultured human fibroblasts have been investigated in the attempt to identify markers for a more accurate quantification of cell injury. Sublethal oxidative stress was obtained by treating fibroblasts with 0.5 mM H2O2 in DMEM plus 5% FCS for times not exceeding 60 min. Under these conditions cells remained viable throughout long-term incubation, showing no appreciable release of cytosolic enzymes into the medium. On the contrary, exposures of fibroblasts to 0.5 mM H2O2 for times > 60 min induced a lethal cell injury which was fully expressed 2 days later by massive monolayer wasting and leakage of cytosolic components. Early metabolic effects of sublethal stress consisted of a rapid and significant fall of both ATP and NAD+ pools. Concomitantly, there was a moderate increase (about threefold) in both ADP-ribosyl transferase activity and free [Ca2+]i, while the specific activity of glyceraldehyde-3-phosphate dehydrogenase was partially decreased upon treatment. Oxidative injury also caused delayed effects consisting of a large depression of both protein and DNA synthesis. However, while the former was partially restored within 10 days of incubation, the latter remained severely impaired, as encountered in a growth-arrested population. Microfilaments of H2O2-treated cells appeared to be morphologically altered due to partial fragmentation of cytoskeleton actin which, however, was still maintained in the polymerized form as F-actin. Moreover, sublethally injured fibroblasts exhibited a reduced adhesiveness to plastic once they were detached and reseeded into new dishes. Relative adhesion efficiencies (number of adherent cells at 16 h as a percentage of seeded cells) were found to correlate inversely with times of exposure to H2O2. This finding allowed the identification of a biological parameter which showed itself to be very sensitive to oxidative stress and was also useful for developing an assay to grade sublethal injury to fibroblasts.

Actin Cytoskeleton↗

PubMed1995

Pole-tracking algorithms for the extraction of time-variant heart rate variability spectral parameters.

Various algorithms of autoregressive (AR) recursive identification make it possible to evaluate power spectral distribution in correspondence with each sample of a time series, and time-variant spectral parameters can be calculated through the evaluation of the pole positions in the complex z-plane. In traditional analysis, the poles are obtained by zeroing the denominator of the model transfer function, expressed as a function of the AR coefficients. In this paper, two algorithms for the direct updating and tracking of movements of poles of an AR time-variant model on the basis of the innovation given to the coefficients are presented and investigated. The introduced algorithms are based upon 1) the classical linearization method and 2) a recursive method to compute the roots of a polynomial, respectively. In the present paper, applications in the field of heart rate variability (HRV) signal analysis are presented and efficient tools are proposed for quantitative extraction of spectral parameters (power and frequency of the low-frequency (LF) and high-frequency (HF) components) for the monitoring of the action of the autonomic nervous system in transient patho-physiological events. These computational methods seem to be very attractive for HRV applications, as they inherit the peculiarity of recursive time-variant identification, and provide a more immediate comprehension of the spectral process characteristics when expressed in terms of poles and AR spectral components.

Algorithms↗

PubMed1998

Myogenic changes of the levator ani muscle in premenopausal women: the impact of vaginal delivery and age.

The aim of this study was to evaluate the impact of parity and age on histomorphology of the pelvic floor muscles in female cadavers of reproductive age and to find out whether there is evidence of myogenic or neurogenic muscle injury. In a cross-sectional study 45 premenopausal unfixed and fresh female cadavers were studied. Four groups were defined: nulliparous and parous women under the age of 40 and over 40 years of age. The pelvic floor was biopsied at six standardized locations. For evaluation of the quantitative parameters and fiber type identification, actomyosin ATPase at pH 9.4 was used. For histomorphological evaluation, sections were stained with hematoxylin/eosin, van Gieson, and Gomori trichrome. The circumference of type I fibers is significantly larger in nulliparous women younger than 40 years compared to nulliparae older than 40 years. Comparing these groups, the form factor of type II fibers also increases significantly, presenting a more circular cell form. Compared to nulliparae, vaginal delivery led to a significant difference regarding the presence of centrally located nuclei, fibrosis, and variation in fiber diameter. In nulliparous women, these significant changes were also found with increasing age. In women with a history of vaginal delivery, no further increase in these characteristics could be detected with increasing age. Comparing the three different biopsy sites, all three changes were more pronounced in the ventral part. There was no evidence of grouped fiber atrophy, small angulated fibers, or type grouping in any of the biopsy specimens. Aging and vaginal childbirth lead to histomorphological changes of the pelvic floor muscle that are consistent with changes of myogenic origin. Evidence of neurogenic damage could not be demonstrated.

Adolescent↗

PubMed1999

Reliable automatic protein identification from matrix-assisted laser desorption/ionization mass spectrometric peptide fingerprints.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry of protein samples from two-dimensional (2-D) gels in conjunction with protein sequence database searches is frequently used to identify proteins. Moreover, the automatic analysis of complete 2-D gels with hundreds and even thousands of protein spots ("proteome analysis") is possible, without human intervention, with the availability of highly accurate mass spectrometry instruments, and high-throughput facilities for preparation and handling of protein samples from 2-D gels. However, the lack of software for precise automatic analysis and annotation of mass spectra, as well as software for in-batch sequence database queries, is increasingly becoming a significant bottleneck for the proteomics work flow. In the present paper we outline an algorithm for reliable, accurate, and automatic evaluation of mass spectrometric data and database searches. We show here that simply selecting from the sequence database the protein that has the most matching fragment masses often leads to false-positive results. Reliable protein identification is dependent on several parameters: the accuracy of fragment mass determination, the number of masses submitted for query, the mass distribution of query masses, the number of masses matching between sample and database protein, the size of the sequence database, and the kind and number of modifications considered. Using these parameters, we derive a simple statistical estimation that can be used to calculate the probability of true-positive protein identification.

Automation↗

PubMed2007

A logistic model for the prediction of the influence of water on the solid waste methanization in landfills.

This article deals with the impact of water content of solid waste on biogas production kinetics in landfills. This impact has been proved in the laboratory thanks to anaerobic biodegradation experiments on paper/cardboard waste samples. A strong dependence with the moisture level was observed for both kinetic rates and maximum methane production. In this article, a logistic model is proposed to simulate the biogas production rate. It is chosen as simple as possible in order to allow for a correct identification of the model parameters given the experimental data available. The moisture dependency is introduced through a linear weighing of the biomass specific growth rate and of the amount of accessible organic substrate. It is directly linked to physical properties of the waste: the holding capacity and the minimal moisture level allowing the presence of free water.

Bacteria, Anaerobic↗

PubMed2005

Double-stranded secondary structures on mRNA induce type I interferon (IFN alpha/beta) production and maturation of mRNA-transfected monocyte-derived dendritic cells.

BACKGROUND: The development of dendritic cell (DC)-based vaccines using antigen-encoding mRNA requires identification of the critical parameters for efficient ex vivo loading of DCs. Exogenously delivered mRNA can induce DC activation, but the molecular mechanisms involved are unknown. The aim of the present study was to identify the means by which mRNA-dependent activation of DCs occurs. METHODS: In vitro transcribed mRNA molecules were delivered into porcine monocyte-derived DCs (MoDCs) using different non-viral gene transfer procedures. Using the green fluorescent protein (GFP) as reporter gene, as well as rhodamine-labeled RNA, intracellular delivery and transfection efficiency were assessed by confocal microscopy and flow cytometry. DC activation was monitored in terms of MHC class II and CD80/86 upregulation, as well as the production of type I interferon (IFN-alpha/beta). RESULTS: mRNA-lipofected MoDCs produced type I IFN and upregulated MHC class II and CD80/86. Computational analysis of the mRNA molecules predicted highly ordered secondary structures forming double-stranded RNA (dsRNA). This dsRNA was also detectable by immunofluorescence in mRNA-lipofected cells, using antibody specific for dsRNA. Digestion of the mRNA prior to lipofection with a double-strand-specific RNase, but not a single-strand-specific RNase, abrogated DC activation. Impairment of protein kinase R (PKR) with 2-aminopurine also interfered with the activation. CONCLUSIONS: Double-stranded secondary structures on mRNA delivered by lipofection can activate MoDCs. This could have important implications for mRNA-based immunomodulation of DCs, DC-based immunotherapy, and formulation of RNA-based vaccines. In addition, this report describes the first in vitro steps towards development of a novel large animal model system to evaluate DC-based vaccines against infectious diseases.

Animals↗

PubMed1995

High resolution quantitative relaxation and diffusion MRI of three different experimental brain tumors in rat.

The potential of quantitative parameter images of the relaxation times T1 and T2, the proton density rho and the apparent diffusion coefficient (ADC) to characterize three different experimental rat brain tumors (F98 glioma, RN6 Schwannoma, and E376 neuroblastoma) was studied. All parameter values, as determined in histologically confirmed regions of interest (ROI), were higher in edema than in tumor, which in turn were elevated with respect to normal brain. ROI values of ADC and T2 delivered statistically significant (P < 0.01) differentiation between tumor and edema. Multidimensional parameter combinations improved differentiation between different tissues. However, the three tumor types could not be differentiated. All parameter maps allowed the identification of the whole tumor-edema area. On T2 images, edema could be identified best, whereas the tumor itself was hardly visualized. In many cases, tumor presentation using T1 maps corresponded best with histology, nevertheless suffering from a poor tumor-edema differentiation.

Animals↗

PubMed2001

Diagnostic and prognostic tumor markers in the gastrointestinal tract.

The gastrointestinal tract is the most common site of malignancies of any anatomic system in the body. An early detection of primary tumors of the bowel, pancreas, liver, stomach, and esophagus is often difficult in asymptomatic patients and for this reason these tumors are often detected at a relatively advanced stage, when symptoms lead to a diagnostic evaluation. Furthermore, gastrointestinal tract tumors have an extremely variable prognosis; thus, the identification of new prognostic parameters may be useful for selecting patients to more tailored therapies. In this work, the main molecular, genetic, tissular, and circulating tumor markers proposed for diagnosis and prognosis of gastrointestinal malignancies are reviewed and discussed.

Biomarkers, Tumor↗

PubMed1994

Latency of skeletal muscle contraction after pulse train stimulation: an important factor in correct timing of skeletal muscle cardiac assist devices.

Various configurations of conditioned skeletal muscle are under investigation for cardiac assistance in patients with end-stage cardiac failure. Optimal timing of conditioned skeletal muscle contraction is essential for effective cardiac augmentation. However, unlike mechanical methods of assistance, skeletal muscle requires time to develop peak tension. We measured "time to 50% peak tension" and "time to 90% peak tension" using an electrical strain gauge in 12 canine latissimus dorsi muscles (6 untrained controls and 6 trained with 3 months of electrical stimulation at 25 Hz with a 15% duty cycle). The "time to 50% relaxation" and the "time to 90% relaxation" after discontinuation of the stimulus were also measured. Conditioned skeletal muscle required significantly more time to develop peak tension than unconditioned skeletal muscle. Relaxation was also significantly prolonged in conditioned muscle. Notably, conditioned lattisimus needed, on average, 0.35 sec to develop peak tension and 0.20 sec for 90% relaxation. Thus, 0.55 sec of each muscle contraction/relaxation cycle was devoted to development of peak tension and subsequent relaxation. At normal canine heart rates of approximately 120 beats per minute (0.50 sec per cardiac cycle), conditioned skeletal muscle may take up to 70% of each cardiac cycle (0.35 sec) to develop 90% of peak tension. The recognition of this phenomenon in conditioned skeletal muscle is important for effective contraction timing of both human and animal skeletal muscle assist devices. Development of proper conditioning regimens for such devices may benefit from identification of those training parameters which produce a minimal "time to peak tension."

Animals↗

PubMed2006

Modeling and observer design for recombinant Escherichia coli strain.

A mathematical model for recombinant bacteria which includes foreign protein production is developed. The experimental system consists of an Escherichia Coli strain and plasmid pIT34 containing genes for bioluminescence and production of a protein, beta-galactosidase. This recombinant strain is constructed to facilitate on-line estimation and control in a complex bioprocess. Several batch experiments are designed and performed to validate the developed model. The design of a model structure, the identification of the model parameters and the estimation problem are three parts of a joint design problem. A nonlinear observer is designed and an experimental evaluation is performed on a batch fermentation process to estimate the substrate consumption.

Bioreactors↗