The measurement of nasal obstruction in clinical
studies of AR can be problematic, as there is no universally
accepted method of assessing this parameter.
Clinical trials of antihistamine treatment for AR take
2 general forms. Allergen challenge chamber (ACC)
studies use specially designed rooms—the Vienna
Challenge Chamber (VCC) or the Environmental Exposure
Unit (EEU)—to measure the response to allergens
and the efficacy of antihistamines under artificial
conditions. Naturalistic studies, on the other hand,
measure the response under conditions found in clinical
practice. ACC studies generate large quantities of
precise and immediately available data. Subjective
data such as individual symptom scores and total
symptom scores (