A system for determining expiratory flow limitation by controlling positive pressure applied during expiration of a breath in a subject, the system comprising: a pressure generator configured to generate a positive pressurized flow of breathable gas for delivery to an airway of the subject; one or more sensors configured to generate output signals conveying information related to breathing of the subject; and one or more hardware processors operatively coupled to the pressure generator and the one or more sensors and configured by machine-readable instructions to: cause the pressure generator to deliver the positive pressurized flow of breathable gas at a set pressure level to the subject for a series of breaths; for at least one selected breath in the series of breaths, cause the pressure generator to adjust the positive pressurized flow of breathable gas by decreasing the pressure level from the set pressure level such that, during exhalation, the positive pressurized flow of breathable gas delivered to the subject is reduced in pressure to a reduced positive pressure for the at least one selected breath; determine EFL in the subject using the output signals from the one or more sensors conveying information related to (a) exhalation for the series of breaths of the subject at the set pressure level and (b) exhalation for the at least one selected breath at the reduced positive pressure level; and automatically adjust, without user intervention, the set pressure level of the pressure generator based on the EFL determination for delivery of the positive pressurized flow of breathable gas to the subject at an adjusted pressure level for at least one subsequent breath. a pressure generator configured to generate a positive pressurized flow of breathable gas for delivery to an airway of the subject; one or more sensors configured to generate output signals conveying information related to breathing of the subject; and one or more hardware processors operatively coupled to the pressure generator and the one or more sensors and configured by machine-readable instructions to: cause the pressure generator to deliver the positive pressurized flow of breathable gas at a set pressure level to the subject for a series of breaths; for at least one selected breath in the series of breaths, cause the pressure generator to adjust the positive pressurized flow of breathable gas by decreasing the pressure level from the set pressure level such that, during exhalation, the positive pressurized flow of breathable gas delivered to the subject is reduced in pressure to a reduced positive pressure for the at least one selected breath; determine EFL in the subject using the output signals from the one or more sensors conveying information related to (a) exhalation for the series of breaths of the subject at the set pressure level and (b) exhalation for the at least one selected breath at the reduced positive pressure level; and automatically adjust, without user intervention, the set pressure level of the pressure generator based on the EFL determination for delivery of the positive pressurized flow of breathable gas to the subject at an adjusted pressure level for at least one subsequent breath. cause the pressure generator to deliver the positive pressurized flow of breathable gas at a set pressure level to the subject for a series of breaths; for at least one selected breath in the series of breaths, cause the pressure generator to adjust the positive pressurized flow of breathable gas by decreasing the pressure level from the set pressure level such that, during exhalation, the positive pressurized flow of breathable gas delivered to the subject is reduced in pressure to a reduced positive pressure for the at least one selected breath; determine EFL in the subject using the output signals from the one or more sensors conveying information related to (a) exhalation for the series of breaths of the subject at the set pressure level and (b) exhalation for the at least one selected breath at the reduced positive pressure level; and automatically adjust, without user intervention, the set pressure level of the pressure generator based on the EFL determination for delivery of the positive pressurized flow of breathable gas to the subject at an adjusted pressure level for at least one subsequent breath.