Nasal cannula devices for insertion in a sleep apnea patient's nasal passages, the device is formed with through air-flow passages and having circular membranes operative upon inhaling by the patient to open for free flow of air into the nasal passages and, further, operative upon exhalation by the patient to block expiration by the patient.The invention further includes a method of providing for free flow of air into a patient's nasal passages upon inhaling and blocking air-flow form the nasal passages during exhalation.
