A system for synchronizing machine-induced expiratory airflow of a subject with user-induced expiratory airflow of the subject, the subject having an airway, the system comprising: (a) a pressure generator configured to generate a pressurized flow of breathable gas for delivery to the airway of the subject at a first pressure level and to reduce pressure of the pressurized flow of breathable gas to a second pressure level that is less than the first pressure level; and (b) a user interface configured to convey indications to a user; characterized in that the system comprises a processor configured to execute computer program modules, the computer program modules comprising: a control module configured to control the pressure generator such that the pressurized flow of breathable gas at the airway of the subject prior to the start of a transition time is at the first pressure level, and such that subsequent to the end of the transition time the pressurized flow of breathable gas at the airway of the subject is reduced to the second pressure level, an indication timing module configured to determine an indicator time prior to the start of the transition time at which an indication should be conveyed to the user to initiate treatment to aid airway clearance of the subject, and a user interface module configured to control the user interface to convey the indication to the user at the indicator time prior to the start of the transition time. (a) a pressure generator configured to generate a pressurized flow of breathable gas for delivery to the airway of the subject at a first pressure level and to reduce pressure of the pressurized flow of breathable gas to a second pressure level that is less than the first pressure level; and (b) a user interface configured to convey indications to a user; characterized in that the system comprises a processor configured to execute computer program modules, the computer program modules comprising: a control module configured to control the pressure generator such that the pressurized flow of breathable gas at the airway of the subject prior to the start of a transition time is at the first pressure level, and such that subsequent to the end of the transition time the pressurized flow of breathable gas at the airway of the subject is reduced to the second pressure level, an indication timing module configured to determine an indicator time prior to the start of the transition time at which an indication should be conveyed to the user to initiate treatment to aid airway clearance of the subject, and a user interface module configured to control the user interface to convey the indication to the user at the indicator time prior to the start of the transition time. a control module configured to control the pressure generator such that the pressurized flow of breathable gas at the airway of the subject prior to the start of a transition time is at the first pressure level, and such that subsequent to the end of the transition time the pressurized flow of breathable gas at the airway of the subject is reduced to the second pressure level, an indication timing module configured to determine an indicator time prior to the start of the transition time at which an indication should be conveyed to the user to initiate treatment to aid airway clearance of the subject, and a user interface module configured to control the user interface to convey the indication to the user at the indicator time prior to the start of the transition time.