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At least 109 records · Page 6Linked to original sources
PubMed1987

Parameter estimation of respiratory impedance measured by forced complex-wave oscillations.

Respiratory impedance data measured using the forced oscillation method were analyzed using an equivalent circuit model and the following conclusions were obtained: 1) Use of the complex wave oscillation method provided a measurement range of over 9 cmH2O/1/s with a resolution of 0.13 cmH2O/1/s. 2) The respiratory system was expressed as a two-compartment model. By expressing the circuit characteristics as phasor loci, a method was shown whereby individual impedance parameter values could be derived from the measured impedance phasor loci. 3) Under enflurane anesthesia, the model parameter values were derived as R1 = 1.2, R2 = 1.6 cmH2O/1/s, C1 = 0.02, C2 = 0.041/cmH2O and L = 0.065 cmH2O/1/s2.

Adult↗
PubMed1989

Minimisation of parameter estimation errors in dynamic PET: choice of scanning schedules.

We addressed the general problem of finding an optimal scan schedule in positron emission tomography (PET) dynamic studies which minimises the errors in estimating the transfer constants between a set of compartments. As an example, the influence of scan intervals in PET on the accuracy of estimation of the rate constants and vascular component in the deoxyglucose method was examined using an empirical noise model. The simulated noisy curves used in the analysis were compared with patient data to validate the noise model. A series of scan schedules were compared for accuracy of fit by evaluating the determinant of the variance-covariance matrix of the fitted parameters as an index of parameter accuracy. For realistic noise levels there is a monotonic improvement in the index of parameter accuracy with increasing sampling frequency, particularly over the initial minutes after the tracer injection. However, since faster schedules are more susceptible to errors introduced by time mismatches between plasma and tissue curves and impose greater computational and memory overhead, an initial scan duration of 30 s provide a practical trade-off for dynamic PET 18F-fluoro-deoxyglucose studies.

Models, Biological↗
PubMed1978

Progress curve analysis in enzyme kinetics: model discrimination and parameter estimation.

The method of progress curve analysis for enzyme-catalyzed reactions (Duggleby, R.G. and Morrison, J.F. (1977) Biochim. Biophys. acta 481, 297--312) has been extended to a two substrate, reversible reaction through the use of enzyme-catalyzed recycling of one of the products. The reaction investigated was that catalyzed by aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) and the product, alpha-ketoglutarate was recycled to glutamate using NADH and NH4Cl in the presence of glutamate dehydrogenase. The values determined for the kinetic parameters of the aminotransferase were found to agree well with those obtained from steady-state velocity measurements. The standard errors of the parameters, as calculated by the procedure originally described, were found to underestimate the observed variation between different experiments. Therefore, a procedure of data compression was devised which leads to more realistic values for standard errors. The compressed data obtained with aspartate aminotransferase have been fitted to the integrated rate equations that describe a variety of kinetic mechanisms. The best fit was obtained with the Ping-Pong model which is applicable to the aspartate aminotransferase reaction. Thus, progress curve analysis may be used to determine the kinetic mechanism of, and values of the kinetic parameters associated with, an enyzme-catalyzed reaction.

Aspartate Aminotransferases↗
PubMed1990

Milk yield increase after anthelmintic treatment of dairy cattle related to some parameters estimating helminth infection.

On 81 farms blood samples were taken from adult dairy cattle, on pasture in October 1986 and after stabling in December 1986, to measure antibody titres against the nematodes Dictyocaulus viviparus, Cooperia spp. and Ostertagia spp., and the trematode Fasciola hepatica, and serum pepsinogen values. Faecal samples, collected in October, were examined to confirm the presence of parasites by means of egg counts and larval identifications. From December until the end of the stabling period, dry cows were either treated with albendazole or left untreated in alternate sequence of calving date. Treated cows produced 132.9 kg milk per cow per lactation more than untreated cows (P less than 0.01). Fat and protein percentage were not significantly influenced by anthelmintic treatment. The mean herd milk yield response to treatment varied from -889 to +1231 kg milk per cow per lactation. There was a significant between-herd variation in antibody titres against nematodes and in pepsinogen values. However no significant correlations between these parameters and the mean herd milk yield response to treatment were found.

Albendazole↗
PubMedDate not supplied

Comparison of nonlinear pharmacokinetic parameters estimated from the sinusoidal perfusion and venous equilibrium models.

It is shown that the intrinsic and steady-state clearances and the values of Vm and Km of the Michaelis-Menten equation estimated via the sinusoidal perfusion model are different from the corresponding values estimated via the venous equilibration model. The liver blood flow rates estimated by two theories (from plasma data) are identical. The comparison was made using the single dose oral and intravenous and steady-state oral plasma concentration-time data for verapamil in six subjects previously published.

Coronary Disease↗
PubMed1992

The effect of influential outliers on parameter estimation in regression analysis.

A comment is made on an article recently published in this journal by Borgeat, Elie, and Castonguay (1991). It is noted that the raw data contained an outlier which is shown to have had a large influence on their estimation of the regression coefficient. Analysis of the data using a nonparametric statistic that is optimal for long-tailed distributions showed that the true regression coefficient is probably smaller than that reported. Other approaches to the analysis of data containing influential outliers are discussed.

Biofeedback, Psychology↗