Methacholine challenge: comparison of two methods.
BACKGROUND
Guidelines for the 2-min tidal-breathing and the five-breath dosimeter methods for methacholine challenge have recently been published by the American Thoracic Society (ATS). Although subjects are exposed to twice as much aerosol at any given concentration during the tidal-breathing method compared to the dosimeter method, they were thought to give equivalent results.


OBJECTIVE
To compare the 2-min tidal-breathing and the five-breath dosimeter methacholine challenges.


METHODS
Tertiary care university-based bronchoprovocation laboratory.


METHODS
Forty subjects with currently symptomatic asthma.


METHODS
The two methacholine tests were done in random order on separate days at the same time of day at 1- to 7-day intervals.


RESULTS
The dosimeter provocation concentration of methacholine causing a 20% fall in FEV(1) (PC(20)) was almost twice that of the tidal-breathing PC(20): 2.4 mg/mL vs 1.3 mg/mL (paired t test, p < 0.00005). The difference was greater in those with mild airway hyperresponsiveness (AHR) [PC(20) > 1.0 mg/mL; 3.2-fold] compared to those with moderate AHR (PC(20) < 1.0 mg/mL; 1.6-fold) [p = 0.04]. Three subjects with mild asthma and mild AHR (tidal-breathing PC(20), 1.9 to 4.3 mg/mL) had a nonmeasurable PC(20) (> 32 mg/mL) with the dosimeter.


CONCLUSIONS
The tidal-breathing method, which exposes the subject to twice as much aerosol at each concentration, produced approximately twice the response. The total lung capacity maneuvers with breathhold during the dosimeter method may inhibit the response in some patients with asthma.
Cockcroft
Donald W
DW
Division of Respiratory Medicine, Department of Medicine, Royal University Hospital, University of Saskatchewan, Ellis Hall, Fifth Floor, Saskatoon, SK, S7N 0W8 Canada. cockcroft@sask.usask.ca
Davis
Beth E
BE
Todd
David C
DC
Smycniuk
Audrey J
AJ
D000328:Adult; D000368:Aged; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology; D001985:Bronchial Provocation Tests / Q000379:methods*; D016085:Bronchoconstrictor Agents; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D016210:Methacholine Chloride; D008875:Middle Aged; D014109:Total Lung Capacity
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride