A nasal cannula includes a cannula body having a passageway extending therethrough from a first end to a second end and an airflow restrictor coupled to the cannula body and positioned to selectively restrict air flow through the passageway during exhalation. A flow regulator is settable to a plurality of airflow positions and cooperates with the airflow restrictor to regulate the air flow during exhalation such that the air flow during exhalation is variable in response to the airflow position of the flow regulator. In one embodiment, an airflow restrictor is deformable from an at-rest configuration to an inhalation configuration during inhalation, and exerts a substantially constant backpressure during exhalation for a predetermined range of expiration flow rate. Methods of use are also provided.
