Dosimeter methacholine challenge: comparison of maximal versus submaximal inhalations.
BACKGROUND
Deep inhalation has bronchodilating and bronchoprotective effects, particularly in subjects who are normal or have mild airway hyperresponsiveness (AHR). We have anecdotally observed that the 5 breath to total lung capacity (TLC) dosimeter method reduced the response to methacholine in some subjects with mild AHR.


OBJECTIVE
To compare prospectively submaximal inhalations with TLC inhalations during the dosimeter methacholine challenge.


METHODS
Sixteen subjects with asthma and a methacholine PC 20 <8 mg/mL performed 2 methacholine challenges in random order; the standard dosimeter method was compared with a modified dosimeter challenge in which methacholine inhalations were performed to approximately 50% to 60% below TLC.


RESULTS
The standard methacholine challenge PC 20 was almost twice that obtained with the modified submaximal inhalation method (geometric mean PC 20, 5.2 mg/mL vs 2.8 mg/mL, respectively; P = 0.0216). In the 5 subjects with the mildest AHR, there was a 2.5-fold to 14-fold difference in PC 20 between methods. The standard (full TLC) PC 20 s were falsely negative (>16 mg/mL) in these 5 subjects with current asthma, 4 of whom required inhaled corticosteroids.


CONCLUSIONS
A submaximal inhalation dosimeter methacholine challenge results in a significantly lower PC 20 compared with the standard 5-breath dosimeter method. This effect is limited to the mildly responsive group, probably because of the bronchoprotective effect of the deep inhalation during the standard method, and results in false-negative tests in some subjects.
Todd
David C
DC
Division of Respiratory Medicine, Department of Medicine, University of Saskatchewan, Royal University Hospital, Saskatoon, SK S7N 0W8, Canada.
Davis
Beth E
BE
Hurst
Thomas S
TS
Cockcroft
Donald W
DW
D000280:Administration, Inhalation; D000328:Adult; D001249:Asthma / Q000175:diagnosis*; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage*; D005188:False Negative Reactions; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D016210:Methacholine Chloride / Q000008:administration & dosage*; D008875:Middle Aged; D009330:Nebulizers and Vaporizers; D013147:Spirometry
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride