Toluene diisocyanate inhalation bronchial callenge test with a closed-circuit device

Occupational asthma is the most common respiratory disease related to the working environmerlts. Isocyanates, especially toluene diisocyanate(TDI), are currently the most common cause of occupational asthma both in Korea and in other industrialized countries. The diagnosis of TDI-induced asthma can be confirmed by inhalation challenge test, usually performed in small challenge room. But there are several pitfalls in this method. Inhsled TDI concentrations can not be checked accurately and may not remain stable throught the procedure. And there are some risk of sensitization to an nonsensitized medical personnel participated in the test. To overcome these problems we simply modified previously reported closed-circuit methodology and made a simple closed -circuit device for challenge test, and then performed inhalation challenge test to 7 bronchial asthmatics who were suspected TDI-induced asthma by personal and occupa- tional history. Of the 7 cases, we designed challenge test to inhsle 20ppb concentrations of TDI for 20 minutes in 5 cases. During inhalation we checked inhaled TDI concentration at 1 minute interval, and the concentrations were frequently exceeded the recommended threshold limit value ceiling(TLVC) of 20ppb in all 5 cases and severe bronchial reactions were noted. Thus 6th case was recommened to inhale subirritant concentration(mean 12.6 + 4.2ppb) of TDI not exceeding the TLVC. After inhalation for 11 minutes, he complained of dyspnea and wheezing, and atypical prolonged immediate reaction was noted on serial pulmonary function monitoring. The last 7th case inhaled compressed air only as placebo on first day and no significant change of FEV20 was seen. On second day he inhaled 4.2+ 1.8ppb concentrstion of TDI for 20 minutes, but no immediate reaction was developed. Thus he inhaled 10.4+2.7ppb concentration of TDI again, and on serial pulmonary function monitoring, isolated late asthmatic reaction was noted. So we concluded that inhalation challenge test with simply modified closed-circuit device was a clinically useful and reliable methodology fot the diagnosis of TDI-induced asthma.ope