Calibrating (electronic) spirometers
Calibrating 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
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.
||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
||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
||Clausen JL. Pulmonary
function testing, guidelines and controversies. Academic
||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.