Patent ID: 8881723

Claim:
A breathable gas supply apparatus for a patient, comprising: a housing having an inspiration chamber and an exhalation chamber, both the inspiration chamber and exhalation chamber being structured to selectively communicate with the atmosphere; a flexible mechanical structure provided to the housing; and a respiratory mask assembly in communication with the inspiration chamber and the exhalation chamber, wherein the flexible mechanical structure is constructed and arranged to: (1) expand in response to a force of patient expiration to draw fresh air from the atmosphere into the inspiration chamber and to allow air exhaled by the patient to accumulate within the exhalation chamber during an exhalation phase of a respiratory cycle of the patient, the expanded flexible mechanical structure adapted to store mechanical energy in the form of mechanical work done by the patient during the exhalation phase, and (2) contract in response to patient inspiration to provide a source of pressurized fresh air at a substantially constant positive pressure from the inspiration chamber to the patient and to provide a force that utilizes stored mechanical energy in the form of mechanical work done by the patient to expunge the exhaled air accumulated within the exhalation chamber into the atmosphere during an inhalation phase of the respiratory cycle of the patient, wherein the flexible mechanical structure includes a weight that is at least partially determinative of the pressure.