Changes of nebulizer output over the years.

The effects of long-term use and of cleaning on the output of 30 specimens of DeVilbiss 646 nebulizers were investigated in order to assess their influence on outcome and interpretation of inhalation provocation tests. Output was assessed in a standardized manner based on weight loss on four occasions one year apart. Output was highly reproducible (intraclass correlation greater than or equal to 0.90), and varied considerably between nebulizers, necessitating calibration at least once. Inadequate cleaning diminished nebulizer output by a factor of two (p less than 0.01), while long-term use was associated with a moderate increase in output of 0.28 mg.yr-1 (p less than 0.0001). Bronchial responsiveness can be underestimated by about one doubling dose due to inadequate cleaning, while interchanging nebulizers can lead to overestimation or underestimation by up to one doubling dose. With proper care the increase in output due to wear has no consequences for clinical practice, or for longitudinal studies.