Assembling control models from pulmonary gas exchange dynamics.

A model abstracts certain features of real systems, which are consistent with the purpose intended for the model. Therefore, models are classified with respect to intended purpose. A structural model predicts behavior based on a hypothetical physiological structure. An empirical model summarizes observed behavior. A functional model attempts to relate observed behavior to physiological structure. It differs from structural model since it includes only structural aspects that are essential for describing the system response. This model classification provides for the interaction among experimental data, underlying physiological hypotheses and experimental design. In this paper, we illustrate the utility of this modeling process for studying pulmonary gas exchange dynamic control processes during exercise. The modeling process is applied to the problem of estimating breath-by-breath gas exchange data, to the problem of selecting appropriate models for characterizing the response to dynamic work rate inputs, and finally to the problem of design of the dynamic aspects of the work rate input.