A tent-like structure has a compact configuration and can be expanded to an expanded configuration large enough totally to enclose a patient. A recirculating gas supply arrangement supplies a mixture of oxygen and helium to the inside of the structure. The structure may contain exercise equipment, such as a static cycle, so that the patient can exercise in the gas mixture. The structure could also be used over a swimming pool. A weight or other means at the lower end of the structure helps to seal it with the floor surface and reduce escape of gas.
