Pulmonary aspects of nitrogen dioxide toxicity

Little is known of the precise location in the respiratory tract where different gaseous pollutants are absorbed. Thus, a model airway was used to study the site and mechanism of nitrogen dioxide (NO2) absorption. The model consisted of sections of perspex tube, representing the conducting airways, connected in series to a larger compartment of variable surface area, analogous to an 'alveolar sink'. The inner wall of the tube was lined with a non-woven polymer fabric, moistened with sterile water, to simulate the surface of the tracheobronchial tree where secretions are greater than 90% water. NO2 gas in nitrogen was passed through the system and its concentration monitored at various positions. It was found that most of the gas reached the larger compartment, confirming that minimal absorption occurs in the upper airways. Thus, NO2 penetrates the gas exchanging region of the lung. In further experiments, a natural pulmonary surfactant (CUROSURF) was exposed to 5 ppm NO2 in nitrogen and post-exposure samples were scanned by electron-spin resonance (ESR) to detect the presence of free radicals. The results were negative. In an adjunct to this study, an aqueous solution of CUROSURF was exposed to NO2 (100 ppm) for 48 h to determine its effect on surface tension. Results have indicated that exposure to NO2 has a marginal effect on the ability of CUROSURF to lower surface tension. (C) 1999 Elsevier Science B.V. All rights reserved.