A supplemental respiratory device is shown that uses electronic components to regulate the flow of a respirable gas to a user, intermittently, on a demmand basis. The present invention, by monitoring small changes in relative airway pressure, caused by the user's inspiratory or expiratory effort, supplies gas only when an inhalation is detected. The present respiratory device can also vary the duration of the gas delivery time to compensate for changes in user breath rate. The invention herein is designed to be compatible with a standard nasal cannula. An electronic apnea detector is shown, and is included in the preferred embodiment of the present invention. In addition, the invention herein, when not used for gas delivery purposes, can be used as a diagnostic device for providing information concerning a user's breathing pattern.