Objective  To investigate the adverse effects of low-concentration isocyanate exposure on airway inflammation and lung function and to explore the application of fractional exhaled nitric oxide (FeNO) in occupational health examinations of isocyanate-exposed workers.

  Methods  From 2016 to 2017, a total of 192 workers exposed to isocyanates were selected as the exposure group, and 91 with similar age and gender composition (office and/or logistics personnel) without any exposure to occupational hazards (as references) were studied. Monitoring data of airborne isocyanate concentration in workplaces in the past 5 years were collected. The basic information of all workers was collected, and their lung function, FeNO, and salbutamol bronchial dilation tests were performed. The differences in various indicators among these two groups of workers were compared.

  Results  The airborne isocyanate concentration in workplaces over the past 5 years was significantly lower than the national occupational exposure limit. The forced vital capacity (FVC) and forced expiratory volume in first second (FEV₁) of the exposed workers were higher than those of the reference group, while FEV₁/FVC was lower than that of the reference group, and the differences were statistically significant (P < 0.001). There was no significant difference in FeNO levels between the exposed workers and the reference workers (P > 0.05). The FEV1/FVC ratio was higher in the exposed workers with exposure time < 7 years than workers with exposure time≥ 7 years (P < 0.05), while there was no significant difference in FeNO levels between these two groups (P > 0.05). There was no significant difference in various indicators of lung function among different workers grouped according to the FeNO levels (P > 0.05). Among 192 exposed workers, 13 had FeNO levels higher than 50 ppb (1 ppb=1×10^-9), and among 9 workers receiving bronchial dilation tests 3 workers were positive.

  Conclusions  FEV₁/FVC could better reflect the adverse effect of isocyanate, a type of asthmagens, on lung function. FeNO levels cannot indicate the occupational low-level isocyanate exposure, while positive changes shown by bronchial dilation tests in exposed populations occur earlier than changes in lung function. The combination of FeNO measurement and bronchial dilation tests could have certain predictive value for diagnosing and screening occupational asthma.