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At least 1,405 records · Page 78Linked to original sources
PubMed1982

A computer program for the analysis of structural identifiability and equivalence of linear compartmental models.

A FORTRAN program based on the sufficient and necessary algebraic condition for structural identifiability is presented. In the case of an unidentifiable model the program generates all identifiable submodels that are structurally equivalent to the original model in the given input--output experiment. The parametrization vector of the model may include first-order and zero-order transport rate coefficients, unknown distribution volumes and initial conditions, as well as unknown elements of input and output matrices. Any a priori constraint imposed upon the parameters may be taken into account. An attempt is made to reduce input data requirements preserving generality of the program.

Computers↗
PubMed1979

A non-linear mathematical model for the in vivo determination of Kupffer cells number and rate of phagocytosis of radiocolloids in rats.

In order to perform a quantification of the hepatic RES function, a mathematical model of the colloids phagocytosis was constructed and validated in normal and partially hepatectomised rats. The experimental design consisted of the collection of successive blood samples for the measurement of radiocolloids time courses after the injection of different doses of gelatin colloids (0.075--5 mg of gelatin/100 g body wt). The unknown parameters were estimated by method of maximum likelihood using a second order algorithm. A good fit between experimental and simulated data was obtained for a large range of injected doses using a single set of parameters. Comparisons of parameters values between normal and hepatectomised rats were found to be -onsistent with the hepatectomy ratio. This computerised estimation of parameters provides a determination of both the total number of Kupffer cells and the mean time of a complete phagocytosis cycle which cannot be obtained by classical approaches.

Animals↗
PubMed1987

A four compartment linear mammillary model.

Studies are made for a four compartment model in which the central compartment is connected reversibly to three other compartments and the elimination occurs from the central compartment only. Identification of different distribution rate constants is made, with concentrations of drug in the central compartment at different times of observation being known. The solution depends on an optimization method in which the different unknowns are reduced to single variable with the help of Archimedes spiral. Thus, the solution requires the global minimum of a functional of single variable. Results are compared with those obtained by the generalized least square method.

Kinetics↗
PubMed1994

A non-linear compartmental model of human basophil activation.

In this paper human basophil activation is modelled by means of a system of differential equations. The resolution of this system allows the justification of the incubation period and the unwedging period existing between the human basophil degranulation and the liberation of histamine.

Algorithms↗
PubMed1990

On the relation between axial resistance and conductivity in linear cable models.

In the classical core conductor model the intra- and extracellular media of an infinitely long nerve or muscle fiber in a volume conductor are represented by parallel axial resistances. Thus, volume conductor properties are neglected. In this paper a study is presented that relates the conductivity of the intra- or extracellular medium of the fiber to the axial resistance used in the core conductor model. Expressions for the axial resistances that are dependent on the spatial frequency of the membrane current source density are derived from a volume conductor approach.

Electric Conductivity↗
PubMed1991

Indistinguishability and identifiability analysis of linear compartmental models.

Two compartmental model structures are said to be indistinguishable if they have the same input-output properties. In cases in which available a priori information is not sufficient to specify a unique compartmental model structure, indistinguishable model structures may have to be generated and their attributes examined for relevance. An algorithm is developed that, for a given compartmental model, investigates the complete set of models with the same number of compartments and the same input-output structure as the original model, applies geometrical rules necessary for indistinguishable models, and test models meeting the geometrical criteria for equality of transfer functions. Identifiability is also checked in the algorithm. The software consists of three programs. Program 1 determines the number of locally identifiable parameters. Program 2 applies several geometrical rules that eliminate many (generally most) of the candidate models. Program 3 checks the equality between system transfer functions of the original model and models being tested. Ranks of Jacobian matrices and submatrices and other criteria are used to check patterns of moment invariants and local identifiability. Structural controllability and structural observability are checked throughout the programs. The approach was successfully used to corroborate results from examples investigated by others.

Computer Simulation↗
PubMed1988

The use of monoamine oxidase inhibition to estimate megakaryocyte-platelet regeneration time (MPRT).

The megakaryocyte-platelet regeneration time (MPRT) was measured in 16 normal subjects after irreversible monoamine oxidase (MAO) inhibition. When ten subjects were given a single 20 mg dose of Parnate (tranylcypromine) the mean MPRT was 242 +/- 20 hours (linear model) or 212 +/- 22 hours (weighted mean model) with a mean %-linearity of 75 +/- 22%. The renewal of platelet MAO activity was initially retarded for about 2 days, suggesting that inhibition of megakaryocyte MAO had occurred. Six subjects who had taken MAO inhibitors daily for 1-6 months gave longer MPRT values (274 +/- 57 hours (lin.) or 246 +/- 67 hours (w. m.)), but the differences between the groups were not statistically significant. The single-dose MPRT results agree well with those obtained using the irreversible inhibition of cyclo-oxygenase by aspirin, but exceed the platelet life-spans estimated using radiochemical methods by about 24-36 hours. Platelet serotonin levels did not change significantly after a single dose of Parnate, but supine systolic blood pressure rose by 9 +/- 7 mm Hg (p less than 0.01) 24 hours after the dose. Estimation of MPRT by MAO inhibition is a useful alternative to the aspirin method but screening of subjects and clinical supervision is needed to avoid hypertensive complications.

Administration, Oral↗