For instance, it would be inappropriate to challenge a nurse with a drug (in powder form) to which she is exposed at work while measuring small quantities into beakers, by asking her to tip large quantities of the material from 1 container to another. The severity of the response that the subject describes occurring at work also needs to be taken into account when devising the challenge.
Initially, short challenge periods are used, perhaps only 1 minute with a 10-minute interval, and lung function is measured before the challenge is repeated for slowly increasing periods of time. Although these forms of challenge are not as well controlled as nebulization, tests that are performed in the same way and for the same duration give reasonably reproducible results. In addition to measuring spirometry, nonspecific bronchial hyperresponsiveness monitored before the challenge and for 7 to 8 hours after the challenge may provide additional useful information; the late asthmatic reaction is associated with temporary increase in bronchial responsiveness that may last for a number of days.
A control day is again necessary, and as far as is practicable the control test should be carried out in a single-blind fashion. The control day for a car spray painter would entail using the spray paint without the isocyanate hardener added. Chemical dusts may be suspended in well-dried lactose, thus disguising their presence. The chemical constituents of solder flux may be manipulated to exclude the chemical being tested on the control day.