Calibration procedure
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See to it that upon connecting the calibrator to the spirometer you cause no air flow through the device: keep the syringe still, avoid a draft through the transducer, as very often this is the moment zero-flow is assessed. It is best to occlude one side of the measuring device when connecting to the calibrator at the start of the calibration procedure. |
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Some spirometers carry out the calibration procedure independently and may have facilities to make appropriate corrections if the result of the calibration is unsatisfactory. Instructions in the manual, or on screen, give guidance how to perform the calibration. |
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Most electronic spirometers are not equipped with an automatic calibration procedure. One should then mimic forced inspiratory and expiratory maneuvers with the calibrated syringe. |
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The measured volume displacement should agree within 105 mL with the volume of the 3 L calibrated syringe. |
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Linearity of the system is assessed as follows. The calibrating maneuver is performed three times at different flows, hence when the piston is moved at different speeds. If the facilities are available, monitor the flow on the spirometer screen and try to maintain expiratory flows of 4, 8, and 12 L/s. The recorded volume should be reproducible: when using a 3 liter calibrated syringe the measured volume displacement should not deviate by more than 105 mL from the target volume, and any deviations from the 3 L volume should be unrelated to the expiratory flow. |
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If the volume calibration does not lead to correct results the user will rarely be able to correct this: the spirometer should then be returned to the manufacturer or dealer. |
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Ideally an electronic spirometer should be calibrated before each session or after ten separate patients have been tested, whichever comes first. In practice this is usually regarded as infeasible. Depending on the intensity of use a calibration needs to be performed each week, or every other week. It is prudent to calibrate each time the spirometer has been cleaned and disinfected. |