| 摘要 |
In a spirometer, a breath transmission passage has first and second ends open to the atmosphere and a given cross-sectional area. A patient breathes through the breath transmission passage bidirectionally. An elongated conduit has a first port at one end, a second port at the other end, and a third port intermediate to the first and second ports to form a first flow measurement passage in the conduit between the first and third ports and a second flow measurement passage in the conduit between the second and third ports. The first and second flow measurement passages have a substantially smaller cross-sectional area than the given cross-sectional area. The breath transmission passage at a point near the first end is coupled by a removable connection to the first port, and the breath transmission passage at a point near the second end is coupled by a removable connection to the second port. The flow resistance between the first end of the breath transmission passage and the third port equals the flow resistance between the second end of the breath transmission passage and the third port. A source of bias gas is connected to the third port. The difference between the rate of gas flow through the first and second flow measurement passages responsive to inhalation from and exhalation to the breath transmission passage is sensed to provide a balanced bipolar indication thereof. In one embodiment, a vacuum pump is disposed between the removable connections and the first and third ports.
|
