Abstract

Background
Exposure to occupational agents can cause immediate asthmatic reactions.

Objective
It can be hypothesized that the pattern of immediate reactions is different for high (HMW)- and low-molecular-weight (LMW) agents. To test this, we studied the temporal features of reactions in workers who underwent specific inhalation challenges for possible occupational asthma.

Methods
We examined 467 immediate reactions due to HMW (n = 248, 53%) and LWW (n = 219, 47%) agents in regards to timing of the maximum reaction and recovery.

Results
The median duration of exposure to elicit significant immediate reactions was comparable for HMW and LMW agents (15 min). The median maximum fall in FEV1 occurred after 20 min for LMW by comparison with 10 min for HMW agents (P < 0.001). The median timing of recovery of FEV1 to 10% baseline was shorter for HMW (60 min) than for LMW (90 min) agents (P < 0.01), and significantly more subjects recovered to 10% baseline (89.5%) for HMW than for LMW agents (72.6%) (P < 0.001). Confounding variables such as age, atopy, baseline airway calibre and the maximum fall in FEV1 at the time of the immediate reaction did not alter the significant effect of the nature of the agent per se. Immediate reactions were followed by a late asthmatic reaction more often in the case of LMW (37.3%) than HMW (26.2%) agents (P < 0.05). Significant changes in non-specific bronchial responsiveness were significantly (P = 0.02) more frequent after reactions to LMW (31.9%) than to HMW (21.4%) agents. We found similar trends by comparing reactions to flour (n = 113), the principal cause of reactions to HMW agents, and diisocyanates (n = 111), the principal LMW agent.

Conclusions and Clinical Relevance
This study shows distinct patterns for immediate reactions due to occupational agents. These results can provide useful guidelines for performing specific inhalation challenges and improve the safety of the procedure.

Full Text

Comments

The paper descibes a very large number of occupational challenges done in Montreal. Immediate asthmatic reactions from low molecular weight antigens on average last 10 minutes longer than those from high molecular weight antigens. The paper also has interesting information on changes in NSBR following a positive challenge, A >3.2 fold change was seen following 32% if HMW and 21% of LMW reactions. This was not related to the magnitude of the immediate reaction. The information on induced sputum is a little unclear, but c45% had <1% eosinophils. Sputum eosiniphilia was not related to the duration of the immediate reaction. As with all retrospective studies of this type, it would have been better to split the population into 2 groups, the first to generate the hypothesis and cut-offs for relevant changes, and the second group to test the hypothesis on data that was not used to generate the hypothesis.

7/5/2012