Assessment of accuracy and applicability of a portable electronic diary card spirometer for asthma treatment.

A pocked-sized turbine flowmeter and spirometer device, integrated with an electronic diary card (EDC-spirometer, Micro Medical, U.K.), was tested with a mechanical calibrator, in an outpatient clinic and in the home situation. A screen pneumotachometer was used as flow and volume reference. Ten devices were tested; interdevice variability was small with a mean variation coefficient of 1.1% for both forced expiratory volume in 1 s (FEV1) and peak expiratory flow (PEF) (SD 0.5 and 0.4, respectively) for eight settings of the calibrator. Mean difference from reference was -0.13 l (SD 0.04) for FEV1 (range 0.38-3.16) and 0.09 l s-1 (SD 0.09) for PEF (range 4.2-11.7). No significant deviation from linearity was present. Results obtained in the outpatient clinic confirmed the accuracy of FEV1 and PEF data obtained with the calibrator. However, linear regression analysis showed a mean underestimation of 0.45 l (SD of estimate 0.29) for forced vital capacity over the whole measurement range, probably due to a restricted integration time. In 10 optimally-treated chronic obstructive pulmonary disease patients in a family practice, PEF measurements were done in the home situation, both with the EDC spirometer and a mini-Wright peak flow meter. No significant differences in the diurnal variation of PEF were found. The PEF data from the mini-Wright meter were corrected for earlier reported flow-dependent systematic deviations. In the home situation, patients preferred the EDC spirometer. It is concluded that this device is applicable in the follow-up and treatment of asthma at home.