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  • Title: Dosimeter methacholine challenge: comparison of maximal versus submaximal inhalations.
    Author: Todd DC, Davis BE, Hurst TS, Cockcroft DW.
    Journal: J Allergy Clin Immunol; 2004 Sep; 114(3):517-9. PubMed ID: 15356550.
    Abstract:
    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. CONCLUSION: 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.
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