Abstract
Ventilation inhomogeneity, an important characteristic of abnormal lungs, is demonstrated in the dynamics of multibreath lung washout. Quantitative evaluation of the washout curve can be obtained from a model-free index, such as a moment ratio, or parameters of a model. Although a moment ratio is easier to compute and less dependent on noise, the parameters of an appropriate model have a direct physiological interpretation. In this study, we develop anN-alveolar-space model from dynamic mass balance equations, which account for breathing pattern variations. The general model takes the form of a set of time-varying, linear difference equations. Special cases of fewer alveolar spaces and time-invariance are examined in more detail. Properties of the time-invariant model are determined with the use of generating functions. In particular, from the generating function of the two-alveolar-space model, the ratio of the first-to-zero moments is expressed in terms of model parameters. If one of the spaces is poorly ventilated, the moment ratio approximately equals the relative volume-flow ratio of that space. As obtained from the model and found experimentally, the moment ratio gets larger as the ventilation inhomogeneity increases.
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Saidel, G.M., Saniie, J. & Chester, E.H. Modeling and moments of multibreath lung washout. Ann Biomed Eng 6, 126–137 (1978). https://doi.org/10.1007/BF02584539
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DOI: https://doi.org/10.1007/BF02584539