Effects of NO2 on chronic bronchitics.

The acute influence of NO2 on mechanics of breathing and respiratory gas exchange was investigated in a total of 111 subjects, aged 25 to 74 years, with chronic nonspecific lung disease (CNSLD). They breathed NO2-air mixtures containing 0.5 to 8.0 ppm NO2 for up to 15 to 60 min. Additionally in nine subjects the protective action of atropine, meclastine, and orciprenaline was investigated. While the alveolar PO2 remained constant during inhalation of 5 and 4 ppm NO2, a significant decrease of the arterial PO2 and a corresponding increase of the arterial to alveolar PO2 gradients occurred. Inhalation of 2 ppm NO2 had not such an effect. Inhalation of NO2 at concentrations down to 1.5 ppm resulted in a significant increase of airway resistance. Lower concentrations had no significant effect. Prolongation of the exposure period from 15 to 60 min at a NO2 concentration of 5 ppm did not result in a more pronounced disturbance of the respiratory gas exchange for oxygen beyond the extent observed after exposure to 5 ppm NO2 for 15 min. Meclastine, in comparison with orciprenaline and atropine, showed a pronounced protective effect on the negative impact of NO2 on respiratory gas exchange and airway resistance. It is concluded that NO2 may act by release of histamine, causing a bronchiolar, alveolar, and interstitial edema, thus differing from irritant air pollutants like SO2, where reflex bronchoconstriction causes in some bronchitics dramatic increases of airway resistance at similar low concentrations.