FIGURE 2.

Diagram of rebreathe apparatus. The patient breathes through a filter and flow meter into a T-piece with two valve-controlled exits: one to room air and one to the rebreathe bag. This is filled with a mixture of air and test gas, and is enriched with O₂ from the test gas. A CO₂ scrubber placed in series removes CO₂ from expired air. The patient breathes either from the rebreathe bag with the air valve closed (wash-in) or breathes room air with the bag valve closed (wash-out).