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Clinical Investigations: ASTHMA |

Methacholine Challenge*: Comparison of Two Methods

Donald W. Cockcroft, MD, FCCP; Beth E. Davis; David C. Todd, MD; Audrey J. Smycniuk
Author and Funding Information

*From the Division of Respiratory Medicine, Department of Medicine, Royal University Hospital, University of Saskatchewan, Saskatoon, SK, Canada.

Correspondence to: Donald W. Cockcroft, MD, FCCP, Division of Respiratory Medicine, Royal University Hospital, Ellis Hall, Fifth Floor, Saskatoon, SK, S7N 0W8 Canada; e-mail: cockcroft@sask.usask.ca



Chest. 2005;127(3):839-844. doi:10.1378/chest.127.3.839
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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.

Setting: Tertiary care university-based bronchoprovocation laboratory.

Patients: Forty subjects with currently symptomatic asthma.

Interventions: 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 FEV1 (PC20) was almost twice that of the tidal-breathing PC20: 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) [PC20 > 1.0 mg/mL; 3.2-fold] compared to those with moderate AHR (PC20 < 1.0 mg/mL; 1.6-fold) [p = 0.04]. Three subjects with mild asthma and mild AHR (tidal-breathing PC20, 1.9 to 4.3 mg/mL) had a nonmeasurable PC20 (> 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.

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