A pressurized flow of breathable gas is delivered to the airway of a subject in accordance with a therapy regimen. The therapy regimen may be designed to maintain oxygenation of the subject. The therapy regimen dictates levels of fraction of inspired oxygen and/or positive end expiratory pressure to maintain a therapeutically beneficial level of oxygenation in a feedback manner. Within the therapy regimen, changes made to fraction of inspired oxygen and/or positive end expiratory pressure automatically and dynamically are constrained by user configured constraints such as the maximum incremental change, amount of time between adjustments, or the maximum rate of change This may provide a level of customization of the automated control of the therapy regime for individual subjects.