Differences in the response to methacholine between the tidal breathing and dosimeter methods: influence of the dose of bronchoconstrictor agent delivered to the mouth.
BACKGROUND
It has been postulated that differences in provocative concentration of methacholine causing a 20% fall in FEV1 (PC20) values between the dosimeter method and tidal breathing method might be due to differences in the dose of agonist delivered to the mouth. The aim of the present study was to determine the influence of the dose of aerosol delivered to the mouth on differences in the response obtained with each challenge method.


METHODS
This study measured airway responsiveness to methacholine by dosimeter method and tidal breathing method in 27 subjects with suspected asthma. The dosimeter was modified to deliver an identical volume to that obtained with the tidal breathing method. Concentration-response curves were characterized by the PC20.


RESULTS
The dosimeter method PC20 was significantly higher than the tidal breathing method PC20, with geometric mean values of 4.03 (95% confidence interval [CI], 1.86 to 8.78 mg/mL) and 2.19 (95% CI, 1.32 to 3.64 mg/mL; p = 0.04), respectively. The mean difference in the PC20 value detected with each method was similar in subjects with tidal breathing method PC20 values > or = 2 mg/mL (0.77 doubling concentrations) and in those with PC20 values < 2 mg/mL (0.96 doubling concentrations; p = 0.83).


CONCLUSIONS
The tidal breathing method produces PC20 values significantly lower than a modified dosimeter method, which delivers the same volume of aerosol. These results suggest that the discordant PC20 values obtained with the two methods are not due to differences in the dose of agonist delivered to the mouth.
Prieto
Luis
L
Seccion de Alergologia, Hospital Universitario Dr. Peset, Valencia, Spain. Electronic address: prieto_jes@gva.es.
Lopez
Victoria
V
Seccion de Alergologia, Hospital Universitario Dr. Peset, Valencia, Spain.
Llusar
Ruth
R
Seccion de Alergologia, Hospital Universitario Dr. Peset, Valencia, Spain.
Rojas
Rocio
R
Seccion de Alergologia, Hospital Universitario Dr. Peset, Valencia, Spain.
Marin
Julio
J
Universidad de Valencia, Valencia, Spain.
D000280:Administration, Inhalation; D000328:Adult; D001249:Asthma / Q000175:diagnosis*; D001985:Bronchial Provocation Tests / Q000379:methods*; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage*; D015331:Cohort Studies; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D016210:Methacholine Chloride / Q000008:administration & dosage*; D009330:Nebulizers and Vaporizers; D011237:Predictive Value of Tests; D013990:Tidal Volume
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride