Dosimeter Method. The allergen is delivered via a dosimeter to deliver known amounts of allergen during each inspiratory maneuver. The number of inspirations is recorded.
Tidal Breathinc Method. The allergen is expressed from a continuous-output nebulizer primed with a fixed volume of allergen solution and delivered via a 500-ml rebreathing bag linked to an oronasal mask for fixed time periods.
In both methods, the same nebulizer should be used throughout the study period for each subject. An initial control day is mandatory, during which the diluent solution is used and lung function is monitored before and for 7 to 8 hours after challenge. This protocol will identify possible nonspecific irritant responses to diluent and also measure diurnal variation in airway caliber, which, when present, may make the interpretation of late asthmatic responses difficult.
The starting dose of allergen may be calculated either from the skin reactivity of the allergen solution (the starting concentration being that which produces less than a 3-mm wheal on prick skin testing of the subject) or by taking 3 to 4 doubling concentrations below the predicted immediate asthmatic response. The allergen is inhaled in increasing concentrations at 10- to 15-minute intervals. In the dosimeter method, these are usually doubling concentrations, with 5 inhalations at each concentration.