title: The effects of particle size on measurement of airway hyperresponsiveness to methacholine.
abstract: BACKGROUND
  The effect of particle size on methacholine provocation concentration causing a decrease in forced expiratory volume of 1 second (FEV1) of 20% (PC20) is debatable.
  
  
  OBJECTIVE
  To evaluate the functional effects of 3 different particle size nebulizers on methacholine PC20.
  
  
  METHODS
  Participants were randomly assigned to have 3 methacholine challenges on 3 separate days. Nebulizer mass median aerodynamic diameter (MMAD) was provided by manufacturers. The Wright nebulizer (MMAD, 1.0 μm), Aeroneb (MMAD, 3 μm), and Aeroneb (MMAD, 5 μm) were calibrated, and the nebulizer outputs were calculated to administer 0.26 mL of methacholine over 120, 112, and 83 seconds, respectively. After each inhalation, spirometry was performed and the test was terminated when the PC20 was achieved.
  
  
  RESULTS
  Eight nonsmoking patients with mild asthma (4 male and 4 female) completed the study. The mean (SD) age was 25 (13.9) years, and the mean (SD) baseline FEV1 was 88% (11.3%). Patients using the Aeroneb (MMAD, 5 μm) nebulizer had the lowest PC20 (bronchoconstricted at lowest methacholine concentration), with a PC20 geometric mean of 0.62 mg/mL compared with patients using the Aeroneb (MMAD, 3.0 μm), who had a PC20 of 1.76 mg/mL, and patients using the Wright nebulizer (MMAD, 1.0 μm), who had a PC20 of 6.32 mg/mL. There was a significant difference in PC20 across all particle sizes (P < .001). The pairwise differences revealed a P < .001 between 3 μm and 1 μm and between 5 μm and 1 μm and a P = .008 between 5 μm and 3 μm.
  
  
  CONCLUSIONS
  Our results reveal a variability in methacholine PC20 using 3 different nebulizers, despite adjusting the nebulizers' outputs. Our results are consistent with the previous reports, which recommended using larger particle size nebulizers in the assessment of airway hyperresponsiveness in asthma.
  
  
  BACKGROUND
  clinicaltrials.gov Identifier: NCT00529477.
authors.affiliation: Cardiorespiratory Research Laboratory, Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Nizar
authors.initials: N
authors.lastname: Naji
authors.forename: Elaine
authors.initials: E
authors.lastname: Keung
authors.forename: Suzanne
authors.initials: S
authors.lastname: Beaudin
authors.forename: James
authors.initials: J
authors.lastname: Kane
authors.forename: Kieran J
authors.initials: KJ
authors.lastname: Killian
authors.forename: Gail M
authors.initials: GM
authors.lastname: Gauvreau
mesh_terms: D000293:Adolescent; D000328:Adult; D016535:Bronchial Hyperreactivity / Q000139:chemically induced / Q000175:diagnosis* / Q000503:physiopathology; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage / Q000737:chemistry*; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008297:Male; D016210:Methacholine Chloride / Q000008:administration & dosage / Q000737:chemistry*; D008875:Middle Aged; D010316:Particle Size; D013147:Spirometry; D055815:Young Adult
chemical_list: D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride