Increase of Exhaled Nitric Oxide (eNO) after Methylene Diphenyl Diisocyanate (MDI) Exposure in Isocyanate Workers with Bronchial Hyperresponsiveness

Background: : Isocyanates have become one of the most important causes of occupational asthma in industrialized countries. Increased exhaled nitric oxide (eNO) levels have been shown to be associated with allergic airway inflammation. The objective of this study was to investigate the influence of isocyanate on eNO levels and to elucidate whether the latter are associated with specific sensitization and/or unspecific bronchial hyperresponsiveness (BHR). Additionally, we wanted to compare eNO changes of smokers and non-smokers. Methods: We determined eNO during diagnostic isocyanate challenges in workers with suspected isocyanate asthma. Results: : Fourteen of 22 symptomatic isocyanate workers showed BHR and five of these 14 developed an asthmatic response upon challenge with methylene diphenyl diisocyanate (MDI). In comparison with the group without BHR, subjects with BHR had higher basal eNO and a significant increase in eNO 22 hrs after MDI challenge. Four of the asthmatic responders and six of the nine MDI non-responders with BHR revealed an eNO increase of > 30%. There was also a positive association between the eNO change and the increase in airway resistance in isocyanate workers with BHR. The highest eNO change was found in subjects with IgE-mediated sensitization to MDI and low MDI thresholds. Only one of the eight MDI non-responders without BHR exhibited an eNO increase of > 30%. Conclusions: : Isocyanate workers with BHR show increased MDI responses both of airway resistance and of the inflammatory marker eNO. eNO measurement is obviously a new suitable tool for monitoring isocyanate workers under respiratory risk