Prolonged bronchial obstruction after a single antigen challenge in ragweed asthma

Some patients with allergic asthma exhibit late-phase responses to inhalation challenge with specific antigen. However, the duration of these responses is difficult to determine because of diurnal variations in airway function, a common phenomenon in patients with asthma. We therefore examined the pattern and duration of pulmonary function in six asymptomatic patients with a history of ragweed asthma and a documented late-phase response after specific and nonspecific bronchial challenge and compared them to responses after control challenge with normal saline. On 3 different days, specific airway conductance (SGaw) and gas distribution by the single breath nitrogen test were measured before (9:00 A.M.) and hourly for 24 hours after inhalation challenge with either normal saline, ragweed extract, or histamine at concentrations sufficient to decrease SGaw immediately by 35% or more. The fluctuations in SGaw after saline and histamine were considerable but failed to follow a typical diurnal or biphasic pattern. There was no difference in mean SGaw between the histamine and saline challenges from 1 to 24 hours after inhalation. In contrast, ragweed challenge produced a typical late-phase response followed by partial recovery of mean SGaw. However, mean SGaw remained subsequently lower than after saline challenge throughout the remaining observation period with fluctuations about this lower level. Gas distribution demonstrated marked intra- and intersubject variations and was therefore not different among the three challenges at any time of measurement. These observations suggest that a single specific but not nonspecific bronchial challenge causes prolonged airflow obstruction in subjects with allergic asthma that lasts 24 hours or longer, independent of variations in baseline airway function.