A system (2, 2', 2'', 2''') for performing respiratory diagnostics is provided that includes a pressure generator (14) configured to generate a first pressurized flow of breathable gas having a first pressure level above atmospheric pressure (e.g., at levels typical of common CPAP devices) and a patient interface device (4, 4', 4'', 4''') coupled to the pressure generator. The patient interface device includes a body (6) having one or more subject interface openings (8) and one or more valves (18, 22, 24) disposed in the body, at least one of the one or more valves being selectively configurable to cause a second pressurized flow of breathable gas to be delivered through the one or more subject interface openings at a selectable pressure level anywhere between the first pressure level and atmospheric pressure in response to the patient interface receiving the first pressurized flow of breathable gas and without receiving any other pressurized flows of breathable gas.
