A breathing gas delivery system and method provides a flow of breathing gas to a patient. The gas flow is purposely interrupted for the patient's exhale phase in order to minimize irritation and injury to nasal tissues due to constant, uninterrupted flows. Embodiments include an oscillating ball valve that interrupts oxygen supply during the patient's exhale phase, cannula tips that are shaped to minimize trauma, and a sleep apnea treatment system that interrupts breathing gas supply during the patient's exhale phase.