VARIATION IN NEBULIZER AEROSOL OUTPUT AND WEIGHT OUTPUT FROM THE MEFAR DOSIMETER - IMPLICATIONS FOR MULTICENTER STUDIES

The active aerosol component of nebulizers is less than 100% of output by weight, and may vary between nebulizers in different batches from the same manufacturer, A measure of bronchial responsiveness to methac holine, which can overcome this problem, is required. One hundred and sixty nebulizers from 21 centres in the European Community Respiratory Health Survey (ECRHS) were calibrated for aerosol and weight output, Methacholine challenge data were obtained for 1,021 subjects in three English centres of the ECRHS, The dose producing a 20% fall in forced expiratory volume in one second (PD20), and log-slope, the regression slope of percentage decline in FEV1 with log (dose), were calculated, with and without calibration of nebulizers by weight. Within-centre va riation in nebulizer percentage aerosol output had a coefficient of va riation of less than 10%, Unlike PD20, log-slope is unaffected by cons tant percentage overestimation of nebulizer output, Variation in outpu t by weight of nebulizers of 10% had little affect an fog-slope. It is , however, affected by the scheduled range of doses. Log-slope shows a dvantages in analysis, and is less affected by variation in nebulizer output, It can be used for multicentre comparisons, with restriction t o a common dose protocol.