A servo ventilator apparatus for controlling pressure support ventilation provided to a patient with alveolar hypoventilation during sleep, comprises a controller 40 configured to control the servo-ventilation of the patient through a patient interface 50 with a flow of pressurized air in accordance with a target ventilation, and means 80 to allow setting an initial target ventilation V1, a final target ventilation V2 and a target ventilation ramp time (t2 - t1). The controller 80 is further configured to control changes to the target ventilation based on the initial target ventilation V1, final target ventilation v2, the target ventilation ramp time (T2 - T1) and a predetermined increasing function of time. The target ventilation is programmed to increase over the target ventilation ramp time until the target ventilation reaches the final target ventilation v2 whereupon the target ventilation stays constant thereafter. The ventilation ramp time (t2 - t1) is at least days long to prevent glottic closure or cessation of respiratory drive.
