A therapy system configured to wash out or flush out the oral and/or nasal cavity to reduce the effective dead space and reduce the work of breathing. The system may displace the expired air in the oral and/or nasal cavity with atmospheric air, or air with altered concentrations, for example, increased humidity, or oxygen levels. A sealed oral interface is provided to the mouth of a patient to supply a volume of pressurized gas. A control system to synchronize the supply of pressurized gas with the patients respiratory cycle. The supply of respiratory gas may be provided during only a portion of the respiratory cycle.
