Difference between dosimeter and tidal breathing methacholine challenge: contributions of dose and deep inspiration bronchoprotection.
BACKGROUND
Two bronchoprovocation methods are widely used. Compared to the tidal breathing method, the dosimeter method delivers approximately half the dose and involves five deep inhalations. Both the lower dose and the bronchoprotective deep inhalations contribute to the lesser airway response of the dosimeter.


OBJECTIVE
To determine the relative role of dose and deep inspiration in the difference between the two methods.


METHODS
Subjects with asthma (n = 24) underwent three methacholine challenges: a dosimeter challenge, a 2-min tidal breathing challenge (twice the dose), and a modified 2-min tidal breathing challenge (twice the dose plus five deep inhalations).


RESULTS
The dosimeter method produced a nonsignificantly lower response than the modified tidal breathing method (p = 0.14). Both deep inhalation methods produced significantly less response than did the standard tidal breathing method (p = 0.011). In the 12 subjects with the most mild airway hyperresponsiveness (AHR), the differences between the deep inhalation method and the tidal breathing method were greater (p = 0.007). By contrast, deep inhalations produced no effect in the 12 subjects with greater AHR; the two tidal breathing methods produced identical results, while the dosimeter produced less response than either (p = 0.033). Six current asthmatics with mild airway responsiveness (tidal breathing method) had negative dosimeter methacholine challenge results.


CONCLUSIONS
In subjects with moderate airway responsiveness, the difference between the methods is due to the difference in dose, whereas in subjects with mild AHR, deep inhalations had a large effect overwhelming the dose effect and producing false-negative methacholine challenge results in 25% of the subjects.
Allen
Nathan D
ND
Royal University Hospital, Department of Physiology, Division of Respirology, Critical Care and Sleep Medicine, 103 Hospital Dr, Ellis Hall, Room 551, Saskatoon, SK, S7N 0W8 Canada.
Davis
Beth E
BE
Hurst
Thomas S
TS
Cockcroft
Donald W
DW
D000280:Administration, Inhalation; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001249:Asthma / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology; D016535:Bronchial Hyperreactivity / Q000175:diagnosis*; D001985:Bronchial Provocation Tests / Q000379:methods; D004305:Dose-Response Relationship, Drug; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006801:Humans; D008297:Male; D036501:Metered Dose Inhalers; D016210:Methacholine Chloride; D011336:Probability; D015656:Respiratory Mechanics / Q000187:drug effects / Q000502:physiology; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D013147:Spirometry / Q000379:methods; D013990:Tidal Volume / Q000187:drug effects
D016210:Methacholine Chloride