A system and method for delivering a flow of breathing gas to an airway of a patient. The system monitors a characteristic that varies based on variations of the flow of the breathing gas and determines a Target Flow for the gas to be delivered to the patient based on the monitored characteristic. The Target Flow is set to a level sufficient to treat Cheyne-Stokes respiration or a sleep disordered breathing event. The system also alters the Target Flow based on a determination that the patient is experiencing a sleep disordered breathing event. In a further embodiment, the system determines an apnea detection time (Tapnea) as Tinsp plus a constant, and delivers a machine triggered breath if an amount since the start of inspiration reaches Tapnea. Yet another embodiment, monitors the characteristic during an inspiratory phase of a respiratory cycle, and controls the flow of gas during the inspiratory phase of the respiratory cycle based on a result of this comparison.
