You would need an air tight cage, an adjustable pressure release valve that works in the range of normal atmospheric pressure (never heard of one of these but it should be possible although most likely expensive), and an air pump.
To lower pressure you have an air tight cage with the air pump setup to suck air out of the cage on the other side you put your pressure release valve. When the pump lowers the pressure in your cage below the selected pressure the pressure release valve will allow air into the tank. You run the air pump continuously to allow for air flow.
To increase the pressure you just flip everything around. So now you pump air into the tank and when the pressure gets to high the release valve lets air out.
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