In the tidal breathing method, 10 fold concentration increases are used. The challenge period at each concentration is 5 minutes. This 5-minute period is further divided into 1-, 2- and 2-minute challenges, with 10 minutes between each challenge. The FEV, is measured at the end of each 10-minute rest period before a further challenge is administered by either method. In general, a 20% fall in FEV, is regarded as a positive response, and when this is achieved, the challenge is stopped. Lung function is measured at 10-to 15-minute intervals for the first hour and then hourly for an additional 7 hours (or longer, if a late asthmatic response is developing).
The dosimeter method and tidal breathing methods of allergen provocation have been compared. Despite the more accurate dose delivery of the dosimeter, the bronchial response with either method is highly comparable.
Occupational Method. For many causes of occupational asthma, challenge with a nebulized solution of the agent is either technically not possible or unsafe. In such cases, an occupational type challenge is performed.- The individuals work situation is simulated as closely as possible within the challenge chamber. This may involve painting, soldering, sanding, or a variety of other activities. It is most important when devising these types of challenge to have a clear idea of how the individual is exposed at work.