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  • Sensitivity analysis  (2)
  • Airway impedance  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 26 (1998), S. 230-241 
    ISSN: 1573-9686
    Keywords: Lung resistance ; Lung elastance ; Airway inhomogeneities ; Viscoelasticity ; Nonlinearity ; Confidence bound ; Sensitivity analysis ; Nonlinear models ; Lung: mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We present a combined theoretical and numerical procedure for sensitivity analyses of lung mechanics models that are nonlinear in both state variables and parameters. We apply the analyses to a recently proposed nonlinear lung model which incorporates a wide range of potential nonlinear identification conditions including nonlinear viscoelastic tissues, airway inhomogeneities via a parallel airway resistance distribution function, and a nonlinear block-structure paradigm. Additionally, we examine a system identification procedure which fits time- and frequency-domain data simultaneously. Model nonlinearities motivate sensitivity analyses involving numerical approximation of sensitivity coefficients. Examination of the normalized sensitivity coefficients provides direct insight on the relative importance of each model parameter, and hence the respective mechanism. More formal quantification of parameter uniqueness requires approximation of the paired and multidimensional parameter confidence regions. Combined with parameter estimation, we use the sensitivity analyses to justify tissue nonlinearities in modeling of lung mechanics for healthy and airway constricted conditions, and to justify both airway inhomogeneities and tissue nonlinearities during broncoconstriction. The tools in this paper are general and can be applied to a wide class of nonlinear models. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8710+e
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-9686
    Keywords: Airway impedance ; Airway resistance ; Airway acoustics ; Airway wall properties ; Airway geometry ; Branching asymmetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Indirect measures of airway diameter such as respiratory system input impedance (Z in) have been widely used to infer or quantify bronchoconstriction, or bronchodilation. One such measure, Z in above 100 Hz has been shown to be primarily influenced by airway geometry and airway walls but not by lung and chest wall tissues. We used a recently developed method based on a complex asymmetrically branched network of tubes with nonrigid walls to analyze Z in from 100 to 2,000 Hz in control and bronchoconstricted (histamine injection) dogs. The resulting estimates of airway diameters indicated that peripheral airways were constricted far more (≈30% of their control diameters) than central airways (i.e., 0% in the trachea). Separate measurements of changes in airway diameters were made in an excised dog lung using high resolution computed tomography. The observed changes in airway diameter between lung volumes of total lung capacity (TLC) and functional residual capacity (FRC) were quantitatively consistent with those obtained from Z indata in our control dogs at FRC. We conclude that this systems identification method can be used to estimate the distribution of airway diameters from Z in.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 26 (1998), S. 488-501 
    ISSN: 1573-9686
    Keywords: Least squares regression ; Analysis of variance ; Laguerre expansion ; Orthogonal algorithm ; Peripheral auditory system model ; Sensitivity analysis ; Kernel ; Nonlinear physiological system identification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Many techniques have been developed for the estimation of the Volterra/Wiener kernels of nonlinear systems, and have found extensive application in the study of various physiological systems. To date, however, we are not aware of methods for estimating the reliability of these kernels from single data records. In this study, we develop a formal analysis of variance for least-squares based nonlinear system identification algorithms. Expressions are developed for the variance of the estimated kernel coefficients and are used to place confidence bounds around both kernel estimates and output predictions. Specific bounds are developed for two such identification algorithms: Korenberg's fast orthogonal algorithm and the Laguerre expansion technique. Simulations, employing a model representative of the peripheral auditory system, are used to validate the theoretical derivations, and to explore their sensitivity to assumptions regarding the system and data. The simulations show excellent agreement between the variances of kernel coefficients and output predictions as estimated from the results of a single trial compared to the same quantities computed from an ensemble of 1000 Monte Carlo runs. These techniques were validated with white and nonwhite Gaussian inputs and with white Gaussian and nonwhite non-Gaussian measurement noise on the output, provided that the output noise source was independent of the test input.
    Type of Medium: Electronic Resource
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