Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “parameter estimation”

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 145 records · Page 8Linked to original sources
PubMed1981

HPLC-analysis and preliminary pharmacokinetic parameter estimations of chloroquine.

An HPLC method for the separate determination of chloroquine and its major metabolites has been developed. Separation was on an octadecyl RP column. Fluorimetric detection followed after on-line post-column buffering of the mobile phase to pH = 9.25. The method is highly selective for the compounds of interest with a detection limit down to 1 ng/ml. Preliminary data on the pharmacokinetics of chloroquine are reported, as obtained with this method. Kinetic parameters were estimated with the aid of the non-linear regression computer programme NON-LIN.

Chloroquine↗
PubMed1986

Logistic curve fitting and parameter estimation using nonlinear noniterative least-squares regression analysis.

A microcomputer program has been developed for the fitting of the logistic curve to biological, medical, and other experimental data. In addition to supplying estimates for all of the logistic curve parameters, the program provides the fitted result for each input datum thus allowing for the immediate assessment of the logistic curve and detection of possible outliers.

Biometry↗
PubMed1990

Parameter estimation in a three-compartment model for blood alcohol curves.

Models of alcohol input and absorption are crucial to the description and understanding of the effects of alcohol in the human body. In this paper, the pharmacokinetics of alcohol after oral administration are described by a three-compartment model with a supposed concentration-dependent absorption and elimination. The absorption of alcohol from the small intestine into the blood is represented by a first-order rate constant ka. To describe the delay in peak concentration of alcohol the gastric emptying rate is represented as a first-order parameter with a feedback control depending on the amount of alcohol remaining in the stomach. The alcohol ingestion can then be represented as a bolus input. The elimination process is described by a model similar to the Michaelis-Menten model for enzyme kinetics. Parameters are estimated by means of an iterative algorithm minimizing a non-linear function. A good fit of the model was obtained for blood alcohol curves from six men and six women who each had received an alcohol dose of 28.5 g on three consecutive days. It is concluded that the model can be recommended to describe adequately the absorption and elimination of alcohol.

Adult↗
PubMed1993

On the covariance between parameter estimates in models of twin data.

We study the covariance between estimates of additive genetic variance and either dominance genetic variance or common environmental variance in likelihood-based twin analyses. The central tools used in these investigations are the asymptotic covariances of variance component estimates, which we present for several commonly used twin models. We first illustrate the use of the asymptotic covariance terms for determining the optimal ratio of monozygotic to dizygotic group sample sizes for a twin study. We then focus attention on the asymptotic correlations between estimates of additive genetic variance, and either dominance genetic variance or common environmental variance, and their use in understanding when parameters are efficiently estimable from twin data. The results of this investigation are confirmed by simulation studies, and highlight inherent limitations of the twin model, in the sense that having only twin data limits the ability to detect individual variance components. Finally, remarks on possible alternative statistical methods are given, and results are presented to illustrate the improvements in efficiency that are possible with additional family data. In particular, the results provide insight into the limitations of inference from twin data.

Analysis of Variance↗
PubMed1995

Accuracy of noncompartmental pharmacokinetic parameters estimated from bolus injection and steady-state infusion data.

A Monte Carlo simulation study was carried out to examine the accuracy of parameters derived from curve moments. Impulse response (IR) and washout (WO) concentration-time curves, based on a triexponential model, were analyzed by numerical integration and regression analysis. Both designs were tested according to their robustness to measurement error and model misspecification. Performance of the methods was judged using the median error (ME) and the median absolute error (MAE) of 1000 simulations. The WO design provided better estimates of mean disposition residence time and worse estimates of the normalized variance of disposition residence times (CVD2) than its rival. At 20% measurement noise, the MAE of CVD2 was less than 13%. The WO design was much more robust to model misspecification. Numerical integration performed as good as, or better than, regression analysis. Both methods are very sensitive to tail-area error, meaning that special attention needs to be paid to this aspect of experimental design. This study demonstrates that it is possible to obtain good estimates of higher moment parameters in a well-designed experiment.

Models, Theoretical↗
PubMed1986

Kinetic model of glucose-6-phosphate dehydrogenase from red blood cells. Parameter estimation from progress curves and simulation of regulatory properties.

A kinetic model of human and mouse glucose-6-phosphate dehydrogenase is presented which takes into account the substrates and all inhibitors of significant importance in the red cell. The parameter values were estimated by analysis of progress curves. The applicability of a new method based on non-linear regression to complex enzyme kinetics was proved. The in vivo-regulation of glucose-6-phosphate dehydrogenase is examined by determining elasticity coefficients and by using simple simulation experiments. The model is convenient to describe the behaviour of enzyme activity under physiological conditions.

Adenosine Triphosphate↗
PubMed1985

Pharmacokinetic calculator program for generation of initial parameter estimates from a three-compartment infusion model.

A polyexponential curve-stripping program, KIN, is described for use on the HP-41CV programmable calculator. The program may be used in the analysis of plasma-concentration-time curves for a three-compartment intravenous bolus or infusion model with linear elimination processes. The coefficients and hybrid rate constants of the exponential function are then used to compute pharmacokinetic parameters (volume of the central compartment, intercompartmental rate transfer constants), which may be used as initial estimates of model parameters in non-linear regression curve-fitting procedures.

Computers↗
PubMed1984

A new method of parameter estimation from progress curves.

A mathematical procedure is presented which permits kinetic parameters to be determined from progress curve data. The method is applicable to any kind of enzymatic reaction which can be described by a single rate equation. A general criterion is derived to check the accuracy of the method. An application to a simulated 2-substrate reaction is given.

Half-Life↗
PubMed1984

Simulation studies of influenza epidemics: assessment of parameter estimation and sensitivity.

The influenza simulation model of Elveback et al is used to evaluate the accuracy of the maximum likelihood procedure of Longini et al for estimating the secondary attack rate in households. The sample population from the Tecumseh Respiratory Illness Study is mapped into the simulation model and simulations are carried out over a range of parameter values and conditions, some of which were derived from influenza seasons in Tecumseh and from the Seattle Flu Study for the years 1975-1980. The estimation procedure is found to be quite robust for parameter values preset within appropriate limits for influenza. However, a significant difference is found between the preset and estimated household contact parameter for epidemics of medium and high intensity when the preset value is zero. Incremental increases in the household contact parameter are shown to produce marked increases in the overall infection attack rate demonstrating that household spread is an important link in maintaining infection in other mixing groups such as schools, preschool groups and neighbourhood clusters of households.

Adolescent↗
PubMed1976

Parameter estimation in studying circadian rhythms.

In the model under consideration for the circadian rhythm study there are three unknown physiological parameters involved: the level, the amplitude and the phase. This paper concerns the estimation of the group level, group amplitude and group phase of a certain group of individuals based on their time series data. Special attention is paid to the amplitude and phase parameters, and solutions are obtained for both the small-sample and the large-sample cases.

Circadian Rhythm↗
PubMed1995

The regulation of malaria parasitaemia: parameter estimates for a population model.

Classical studies of non-immune individuals infected with Plasmodium falciparum reveal that the infection may be regulated for long periods at a relatively stable parasite density, despite the enormous growth potential of a parasite that continually replicates within host erythrocytes. This suggests that the parasite population may be controlled by density-dependent mechanisms, and in theory the most obvious of these is competition between parasites for host erythrocytes. Here we evaluate the role of this mechanism in the regulation of parasitaemia, by modelling the basic population interaction between parasites and erythrocytes in a form that allows all the essential parameters to be estimated from clinical data. Our results show that competition cannot account for the total regulation of P. falciparum, but when combined with immune mechanisms it may play a more important role than is generally supposed. Further analysis of the model indicates that in the long term, parasite replication at low parasite densities can contribute significantly to the high degree of anaemia observed in natural infection, a conclusion which is not obvious from simple clinical observation.

Anemia↗
PubMedDate not supplied

Model parameter estimation and analysis: understanding parametric structure.

We developed three algorithms to facilitate an analysis of the parameter combinations (PASS points) that fit experimental data to a desired degree of accuracy. The clustering algorithm separates PASS points into clusters (PASS clusters) as a preliminary step for the following geometrical parametric analyses. The PASS region reconstruction algorithm defines the space of a PASS cluster to allow further parametric structural analysis. The feasible parameter space expansion algorithm produces a complete PASS cluster to be used for model predictions to evaluate the effects of variability and uncertainty. These algorithms are demonstrated using two pharmacokinetic models; a single compartment model for procainamide and a three-compartment physiologically based model for benzene. We found a more thorough representation of the parameter space than previously considered. Thus, we obtained model predictions that describe better the variability in population responses. In addition, we also parametrically identified a subpopulation that may have a higher risk for cancer.

Algorithms↗
PubMed1976

The comparison of parameters estimated from several different samples by maximum likelihood.

A system of computer programs has been developed to compare the parameters of several samples taken from populations with arbitrary but known distribution functions. The user indicates which of the parameters are assumed to be equal in all populations under the null hypothesis alone or under both the null and the alternative hypotheses. The programs perform maximum likelihood estimation under the general and the restricted model and also calculate the values needed for a likelihood ratio test. The programming language used was PL/I-FORM AC. An illustrative numerical example is given.

Animals↗
PubMed1989

Anaerobic threshold: reproducibility out from ventilatory parameter estimation.

Anaerobic threshold (AT) during exercise is usually noninvasively determined by assuming a two-segment mathematical relationship between two ventilatory parameters. In the literature, all the possible pairs of segments are first considered, and the most appropriate pair is then selected according to at least-squares method. In such a model, the AT is considered to be related to the joining point of the two segments. In order to test the reliability of the model, we compare the results of the least-squares method to those based on maximum probability method in discriminating the two regression coefficients. In order to test the reproducibility of the two different criteria, comparisons have been repeated after data have been filtered. A paired t test was used to carry out comparisons. Ventilatory parameters were collected in 10 healthy subjects during the use of a bicycle ergometer. The required power was increased every 15 s by steps of 30 W, starting from 50 W. Ve, VO2 and VCO2 have been sampled every 15 s, then the three functions--Ve versus VO2, Ve versus VCO2 and VCO2 versus VO2--were considered. Each function was stylized with two linear segments. Each segment was estimated by using a second-kind linear fitting. We verified that: (i) the AT may be reliably appreciated depending on the pair of selected parameters; (ii) only when data are smoothed is no difference between the two criteria documented (Ve vs. VO2, p = 0.99; Ve vs. VCO2, p = 0.54); (iii) no significant difference, related to smoothing, is documented both in using the least-squares method (Ve vs. VO2, p = 0.61; Ve vs. VCO2, p = 0.15) and the maximum p level criterion (Ve vs. VO2, p = 0.59; Ve vs. VCO2, p = 0.19).

Adolescent↗
PubMed1987

PEDA: a microcomputer program for parameter estimation and dosage adjustment in clinical practice.

PEDA, an integrated program in BASIC for implementation on microcomputers, has been developed for use in clinical practice to assist dosage adjustment for individual patients. A parameter optimization for individual patients is based on the principle of Bayes' theory and Maximum Likelihood Estimation, and utilizes a prior information on the distribution of population pharmacokinetic parameters, means and variances, as well as serum drug concentrations. The program can accommodate a one-compartment open linear model and a non-linear model at steady state (Michaelis-Menten model) and handle both uniform and non-uniform multiple dosage regimens mostly arising from clinical settings. Clinical examples which demonstrate the ability and the flexibility of the program are provided. The program may also be used as an aid for instruction in clinical pharmacokinetics.

Adult↗
PubMed1977

Respiratory parameter estimation using forced oscillatory impedance data.

The frequency dependency of the magnitude and phase angle of total respiratory impedance was measured in apneic dogs at functional residual capacity during forced oscillation by a special electronics unit. Regression analysis of these data yielded estimates of total respiratory resistance (RFO), inertance (IFO), and compliance (CFO). After correcting for the effects of the endotracheal tube, mean control values (+/-SE) of RFO, IFO, and CFO for the clinically normal dogs were 1.30+/-0.10 cmH2O-1-1-s, 0.0114+/-0.0022 cmH2O-1-1-s2, and 0.0306+/-0.0009 1-cm H2O-1, respectively. Estimates obtained with added resistance, a less dense gas, and abdominal weighting were consistent with predicted effects. In four dogs with mild respiratory symptoms, mean RFO was significantly elevated with no change in IFO or CFO. Independent measurements of resistance and compliance during tidal ventilation correlated well with RFO (r=0.87) and CFO (r=0.80), but RFO and CFO were, on the average, 71% of the tidal breathing values. Thus, the method provides precise estimates of RFO, IFO, and CFO, and allows detection of small changes in these parameters.

Airway Resistance↗
PubMed1982

Analytical approximations of sensitivities of steady state predictions to errors in parameter estimation.

The sensitivity theory is applied to derive a linear approximation to the functional dependence of some steady state quantities of therapeutic significance on pharmacokinetic parameters obtained from the biexponential response to a single drug dose. The error of a steady state prediction depends in general on two terms. The first one may be viewed as an approximate sensitivity of the prediction to the parameter errors, and this depends solely on the algebraic relation between the prediction and the parameters. The second term is the relative error in parameters, and this may be affected by experimental design and the method of data analysis. Comparisons are made with Monte Carlo simulations and "a posteriori" estimates of variance of a prediction.

Kinetics↗