An apparatus for providing ventilatory support to a patient, said apparatus comprising an interface (2) to the patient's airway； a supply (1) of breathable gas coupled to said airway interface； a controller (10) configured to control the supply of breathable gas to vary the pressure at the patient interface (2) so as to provide ventilatory support to the patient during inspiration and expiration； and a means of determining respiratory airflow, wherein during expiration the controller (10) is adapted to continually adjust the expiratory pressure to substantially prevent dynamic airway compression and to balance the intrinsic positive end expiratory pressure.
