A physiological control is a human subject (usually a staff member or members) who tests the spirometer on a regular basis.

A physiological control, also know as a biological control, involves a member of staff performing spirometry on themselves on a regular basis (usually weekly), to check that the spirometer is measuring within their acceptable range. The values monitored include the FEV1 and FVC values, and PEF if using a flow measuring device.

Deviation from their normative values could indicate a problem with the spirometer, the software, circuitry, or the syringe.

Of course the subject performing biological controls must be free from respiratory disease, particularly asthma where variability in FEV1, FVC, and PEF is expected.

Biological control data must be logged electronically and recorded as a hard copy. Data sets should be averaged and a 5% variability from the mean recorded.

Here is an example of how this data is calculated. To emphasise best practice, a 2.5% variability above and below the mean is used, however 5% above and below the mean is acceptable.