The flow measuring technology used by Vitalograph in its monitoring and screening devices is the stator rotor. Stator-rotor devices are used for less robust and accurate devices such as screeners and monitors. Such devices are also difficult to clean and their limited life makes them unsuitable for satisfactory spirometry examinations, although they are ideal for screening and are cheap to replace.
This spirometric measuring technology is often incorrectly classified as a ‘turbine’. (A turbine has a curved blade and requires no stator). All stator-rotor and turbine systems have difficulty measuring low flows because of the compromise with flow impedance. Rather than risking dubious FVC readings in airways obstruction cases, Vitalograph devices use a definite validated surrogate measure, FEV6.
Unlike in a turbine the air spins in a stator-rotor system, which is developed by a multi-vaned stator inducing swirl on the airflow which makes a flat blade (the rotor) spin. The blade blocks a light source as it spins and a detector arrangement allows a measure of the mass air flow by counting the revolutions. The rotor rotates at a speed approximately proportional to flow. Devices are calibrated at the time of production.