Parameter Estimation for Linear Compartmental Models—A Sensitivity Analysis Approach
Abstract
Linear compartmental models are useful, explanatory tools, that have been widely used to represent the dynamic behavior of complex biological systems. This paper addresses the problem of the numerical identification of such models, i.e., the estimation of the parameter values that will generate predictions closest to experimental observations. Traditional local optimization techniques find it difficult to arrive at satisfactory solutions to such a parameter estimation problem, especially when the number of parameters is large and/or few data are available from experiments. We present herewith a method based on a prior sensitivity analysis, which enables division of a large optimization problem into several smaller and simpler subproblems, on which only sensitive parameters are estimated, before the whole optimization problem is tackled from starting points that are already close to the optimum values. This method has been applied successfully to a linear 13-compartment, 21-parameter model describing the postprandial metabolism of dietary nitrogen in humans. The effectiveness of the method has been demonstrated using simulated and real data obtained in the intestine, blood and urine of healthy humans after the ingestion of a [15N]-labeled protein meal.
Keywords
Biological system modeling Inverse problem Parameter estimation Optimization methods Sensitivity Algorithms Compartmental models Nitrogen metabolism Dietary proteins Tissue distributionAbbreviations
- BU
body urea
- CV
coefficient of variation
- d0
noise-free data
- d1
low homogeneous noise data
- d2
high homogeneous noise data
- d3
high heterogeneous noise data
- E
ileal effluents
- G
gastric content
- IL1
proximal intestinal lumen
- IL2
distal intestinal lumen
- LLF
log of the likelihood function
- N
nitrogen
- ODE
ordinary differential equations
- PAA
peripheral free amino acids
- PP
peripheral proteins
- SA
sensitivity analysis
- SAA
splanchnic free amino acids
- SCP
splanchnic constitutive proteins
- SEP
splanchnic exported proteins
- UU
urinary urea
- UA
urinary ammonia
Notes
Acknowledgments
The authors would like to thank M. P. Saccomani from the University of Padova (Padova, Italy) for having checked the a priori identifiability of the studied model, and for helpful and constructive discussions on the global a priori identifiability of compartmental models. The authors also thank E. Cancès from the École Nationale des Ponts et Chaussées (Paris, France) and P. Michel from the École Nationale Supérieure (Paris, France) for helpful and stimulating discussions.
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