Validity of the "airflometer"--a simple device for assessment of forced expiration

The device is basically a plastic turbine with a reduction gear (approximately 1:300) driving an indicator. Following a forced expiration on the indicator comes to rest after about 30 s, when it is read. The reading appears to be generated by the expired flow versus time pattern, and during a forced expiration, close to maximum speed for the turbine is reached within 0.5 s. In a given subject repeated measurements with the same apparatus varied within a few per cent, whereas the variation was considerable among different apparatuses. Readings correlated about equally well with FEV0.5 and FEV1.