Pulmonary effects of a polyisocyanate aerosol: hexamethylene diisocyanate trimer (HDIt) or Desmodur-N (DES-N).

Desmodur-N (DES-N) or hexamethylene diisocyanate trimer (HDIt), a biuret structure of hexamethylene diisocyanate, is a viscous liquid used for durable coatings and is applied by brushing or spraying. DES-N aerosol has been shown to be primarily a pulmonary irritant following a single exposure in mice. To explore the pulmonary effects of this agent further, groups of guinea pigs were exposed to concentrations ranging from 8 to 121 mg/m3 of DES-N for 3 hr. Prior to and following exposure, each animal was challenged with 10% CO2 in 20% O2 and 70% N2 to evaluate their pulmonary performance. Following a single exposure, these animals displayed a concentration-dependent increase in respiratory rate and decrease in tidal volume, as well as coughing and apnea. Their ventilatory response to 10% CO2 was abnormal and characteristic of a lung restriction response. Some airflow limitation was seen during expiration but this occurred more often during air breathing than during CO2 challenge. With daily exposures repeated for 11 consecutive days, guinea pigs began to adapt to the exposures as indicated by a return to a normal ventilatory response to CO2. This adaptation occurred within the first 5 days of exposures. From Days 6 to 11, there was a demonstrable effect, but the level of response was much less than that following the first exposure. No cumulative effect could be demonstrated with this polyisocyanate and the effect was found to be different than that for mono- or diisocyanates. Acceptable levels of exposure to this polyisocyanate for industrial workers are suggested.