INCREASE IN NONSPECIFIC BRONCHIAL HYPERRESPONSIVENESS AS AN EARLY MARKER OF BRONCHIAL RESPONSE TO OCCUPATIONAL AGENTS DURING SPECIFIC INHALATION CHALLENGES

Background - Specific bronchial reactivity to occupational agents may decline after exposure in the workplace ceases leading to falsely nega tive specific inhalation challenges. A study was carried out to assess prospectively whether increases in nonspecific bronchial hyperrespons iveness could be useful in detecting the bronchial response to occupat ional agents during specific inhalation challenges. Methods - Specific inhalation challenges were performed in 66 subjects with possible occ upational asthma due to various agents. After a control day the subjec ts were challenged with the suspected agent for up to two hours on the first test day. Those subjects who did not show an asthmatic reaction were rechallenged on the next day for 2-3 hours. The provocative conc entration of histamine causing a 20% fall (PC20) in the forced expirat ory volume in one second (FEV(1)) was assessed at the end of the contr ol day as well as six hours after each challenge that did not cause a greater than or equal to 20% fall in FEV(1). The subjects who had a si gnificant (greater than or equal to 3.1-fold) reduction in PC20 value at the end of the second challenge day were requested to perform addit ional specific inhalation challenges. Results - The first test day eli cited an asthmatic reaction in 25 subjects. Of the other 41 subjects f ive (12%, 95% confidence interval (CI) 4% to 26%) exhibited a greater than or equal to 3.1-fold fall in the PC20 value after the inhalation challenge and developed an asthmatic reaction during the second (n = 3 ) or third (n = 2) challenge exposure. The offending agents included p ersulphate (n = 1), wood dust (n = 2), isocyanate (n = 1), or amoxycil lin (n = 1). These five subjects had left their workplace for a longer period (mean (SD) 21 (14) months) than those who reacted after the fi rst specific inhalation challenge (8 (11) months). Conclusions - The i ncrease in non-specific bronchial hyperresponsiveness after a specific inhalation challenge can be an early and sensitive marker of bronchia l response to occupational agents, especially in subjects removed from workplace exposure for a long time. Non-specific bronchial hyperrespo nsiveness should be systematically assessed after specific inhalation challenges in the absence of changes in airway calibre.