Detection gas circuit and expiration diagnostic instrument

The invention provides a detection gas circuit and an expiration diagnostic instrument, and relates to the technical field of clinical diagnosis. The detection gas circuit comprises a detection gas circuit body, a gas storage part and a first switch part, the detection gas circuit body is provided with a gas inlet end, and the detection gas circuit body can receive and detect gas to be detected; the gas storage part is mounted at the gas inlet end through the first switch part and is provided with a gas storage cavity capable of receiving gas to be detected; wherein the gas storage cavity is configured as follows: the capacity of the gas storage cavity can be changed along with inlet and outlet of gas to be detected, and the gas storage cavity has a zero-capacity state; and the first switch piece is configured to at least switch the on-off state between the gas storage cavity and the detection gas path body. According to the device, to-be-detected gas collection and measurement gas path body vacuumizing can b