A General-Purpose Model for Investigating Dynamic Cardiopulmonary Responses During Exercise

Abstract

Among the essential features of a heuristic physiological model are that it summarizes the available knowledge regarding a particular system and allows investigation of the consequent implications of the chosen model structure on a range of physiological responses. Our approach here was to pursue the latter feature, as it is evident that physiological inferences are often drawn in the literature without actual determination of whether the inferred behavior is, in fact, achievable with the given model. Hence, our purpose was to choose an explicit model that describes certain observed features of the body’s gas-exchange control system, and to determine the necessary consequences imposed by its structure on the observable behavior, under specified stimuli of physiological interest. We therefore required that: (a) the explicit model be sufficiently general to allow such determination without restricting it to espouse solely any particular control-system hypothesis, and (b) it allow progressive incorporation of particular observed behavior, thus developing in complexity (and completeness) in a “building-block” fashion. We found that surprising consequences often attended the simplest of stimulus profiles when constrained by the chosen model structure. But although intuition can be significantly misleading, it can be appropriately redirected by observing calculated variables when the (assumed) model is challenged over a suitable range of stimuli.