Sensing airflow and delivering therapeutic gas to a patient. At least some of the example embodiments are methods including: titrating a patient with therapeutic gas during a period of time when a flow state of breathing orifices is in a first state, the titrating results in a prescription titration volume； and then delivering the prescription titration volume of therapeutic gas to the patient when the flow state of the breathing orifices is in a second state different than the first state, the delivering only to the breathing orifices open to flow.
