Described here are methods for altering the flow of air in a respiratory cavity such as the nostrils of the nose. These methods and devices may be useful for affecting a physiologic benefit in patients suffering from a variety of medical diseases, particularly those that may benefit from "pursed-lip" breathing and non-invasive ventilation, such as COPD, heart failure, sleep apnea, and other medical disorders. The devices are typically removable devices that may be placed over or in a respiratory cavity to increase resistance to airflow within the respiratory cavity. Resistance to expiration may be selectively increased relative to inspiration. Removable nasal devices are described.