Described herein are adjustable-resistance respiratory devices, and particularly nasal devices that have an adjustable expiratory resistance while providing a greater resistance to exhalation than to inhalation. The resistance to exhalation may be manually adjustable by a user or remotely adjustable by a third party. For example, described herein are nasal devices having a greater resistance to exhalation than inhalation that includes one or more resistance-modifying members for modifying the resistance of a nasal device. A resistance modifying member may include a cover, a shutter or an adjustable valve for opening/closing a leak pathway through the nasal device. An adjustable-resistance nasal respiratory device may include a control or controls for adjusting the resistance to exhalation. Methods of adjusting the resistance of a nasal device, and systems including nasal devices allowing the resistance to be optimized and/or adjusted are also described.