Effect of challenge method on sensitivity, reactivity, and maximal response to methacholine.
BACKGROUND
Recent data suggest that the tidal breathing method may produce methacholine provocation concentration that caused a decrease in forced expiratory volume in 1 second of 20% (PC20) values significantly lower than the dosimeter method; however, the effect of the challenge method on the shape of the concentration-response curve has not been investigated.


OBJECTIVE
To determine the effect of the challenge method on sensitivity, reactivity, and maximal response to methacholine.


METHODS
We measured airway responsiveness to methacholine using dosimeter and tidal breathing methods in 30 individuals with suspected asthma. Concentration-response curves were characterized by their PC20 (sensitivity), slope (reactivity), and, if possible, level of plateau.


RESULTS
Dosimeter PC20 values were significantly higher than tidal breathing values (geometric mean, 8.9 and 5.2 mg/mL, respectively); the mean difference in PC20 values obtained using each method was 0.78 doubling concentrations (P = .01). The mean slopes were 22.7%/log mg/mL using the tidal breathing method and 24.9%/log mg/mL using the dosimeter method; the mean difference in the slopes obtained using each method was -2.17%/log mg/mL (P = .18). In 10 individuals who showed a plateau with the 2 methacholine challenge tests, the mean level of plateau was 19.8% using the tidal breathing method and 19.5% using the dosimeter method; the mean difference in the plateau values obtained with each method was 0.3% (P = .87).


CONCLUSIONS
Although the tidal breathing method produces methacholine PC20 values significantly lower than the dosimeter method, both methods provide similar values for slope and level of plateau. These results suggest that the technical factors that affect methacholine sensitivity and the shape of the curve are different.
Prieto
Luis
L
Sección de Alergología, Hospital Universitario Dr Peset, Valencia, Spain. prieto_jes@gva.es
Ferrer
Ana
A
Domenech
Juan
J
Pérez-Francés
Carmen
C
D000280:Administration, Inhalation; D000328:Adult; D001249:Asthma / Q000175:diagnosis*; D001985:Bronchial Provocation Tests / Q000379:methods*; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage*; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006801:Humans; D008297:Male; D016210:Methacholine Chloride / Q000008:administration & dosage*; D012680:Sensitivity and Specificity; D013990:Tidal Volume / Q000187:drug effects
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride