Aim: To measure the effect of an in-line microaerosol filter on spirometric values in cystic fibrosis (CF).
Methods: Twenty-six subjects with CF undertook a randomized, open, cross-over comparison of spirometry with and without an in-line filter.
Results: The filter had no significant effect on spirometric parameters nor was there any order effect. Measurement error was unrelated to the magnitude of the measurement.
Conclusion: In-line microaerosol filters do not affect spirometric values or variability in children with CF.