Measurement of FEV1 and FVC. Comparison of a pocket spirometer with the Vitalograph.

The performance of a pocket spirometer was compared with that of the Vitalograph to assess the extent of agreement between the instruments and the repeatability of measurements with each instrument. Both instruments showed a similar level of accuracy when measurements were repeated and in the estimation of forced vital capacity, but there was a mean difference of 201 ml in measurements of forced expiratory volume in one second, for which the Vitalograph gave the larger reading.