Bronchial Provocation Tests
To guarantee a meaningful performance of the MCC, patients had to follow the preparation guidelines(3, 9). The administration of the MCC was largely automated according to the 1-concentration-4-step dosimeter protocol(10) which promises advantages in dosing accuracy and handling. Briefly, spirometry was performed at baseline as a first step, followed by four steps, each with the inhalation of methacholine and subsequent spirometry two minutes after inhalation. With each step the inhaled methacholine dose was raised, starting from 15 μg and increasing to a maximum of 720 μg. The exact dose inhaled at each step was determined by measuring the effective nebulization time at inspiration and referring it to the drug concentration and nebulizer power. The complete procedure was realized with the MasterScreenTM Body system (CareFusion, Höchberg, Germany) powered by the Sentry Suite software (Version 2.17.66, Hotfix Package 4) with automated control, providing a real-time visualization of the dose administration and breathing pattern. To optimize the inhalation process, patients could control their breathing themselves by a visual computer graphic imitating their breathing to attain an airflow of 0.5 L/s and to guarantee an inspiration time of 3 seconds during inhalation. The aerosol for inhalation was generated directly by the flow-triggered nebulization of a solution with a constant methacholine concentration (16 mg per mL isotonic saline(11)) through a mouthpiece of an APSpro jet-type nebulizer (240 mg/min performance; Medic Aid pro; Sidestream Care Fusion).
The current, as well as the cumulative, methacholine dose (PD20) which caused a decrease of FEV1 by more than 20% was calculated by logarithmic interpolation. The end-of-test criterion was met if either FEV1 decreased by more than 20% or the maximum cumulative methacholine dose of 960 μg had been inhaled. The result of the MCC was assessed as positive if PD20 was lower than 960 μg.