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Calibrating (electronic) spirometers

Calibration syringeCalibrating an electronic spirometer is best performed by calibrating the primary signal: flow. The procedure, however, is complex and not easily performed by the end user. Volume calibration is a satisfactory alternative (ref. 1). This comprises calibration of the combination of flow meter and integrator. It is performed with a 1 or 3 liter syringe; the 3L syringe is to be preferred. These instruments are expensive but very accurate, robust, and easy to use.

Calibration procedure

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.
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.
  Most electronic spirometers are not equipped with an automatic calibration procedure. One should then mimic forced inspiratory and expiratory maneuvers with the calibrated syringe.
  The measured volume displacement should agree within 105 mL with the volume of the 3 L calibrated syringe.
  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.
  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.
Ideally an electronic spirometer should be calibrated each time it is turned on (and preferably at regular intervals during the day). 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.

Ref. 1 - Using a calibrated syringe
1 Clausen JL. Pulmonary function testing, guidelines and controversies. Academic Press 1982.
2 Quanjer PhH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault JC. Lung volumes and forced ventilatory flows. Eur Respir J 1993; 6 suppl. 16: 5-40. Erratum Eur Respir J 1995; 8: 1629.
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