Uniqueness of optimal controllers during exercise

The optimization hypothesis of respiratory control during exercise is based on the minimization of a function reflecting both chemical and mechanical costs. Both additive and multiplicative controllers have been derived as optimal from similar cost functions. The purpose of the present study was to explore the uniqueness of such predictions. Various formulations of controllers compatible with isocapnia were found to yield identical costs as controllers predicted to be optimal. It was concluded that controller predictions based on optimization theory are not unique. Optimization can occur with either an additive or multiplicative controller or any combination of the two which satisfies an isocapnic constraint. A general form of a combined additive-multiplicative controller was derived which was found to be compatible with previously reported experimental data collected during combined CO2 inhalation and exercise.