Short-term exposure to air pollution in a road tunnel enhances the asthmatic response to allergen

The aim of this study was to assess whether air pollution in road tunnels w ould promote asthmatic reactions in persons with mild allergic asthma. Twenty volunteers with mild allergic asthma were exposed, inside a car, for 30 min in a Stockholm city road tunnel. As a control, the subjects were ex posed to much lower pollution levels in a suburban area. Four hours after t he exposure, the subjects inhaled a low dose of allergen. Asthmatic reactio n during the early phase was measured as the increase in specific airway re sistance 15 min after allergen inhalation and during the Late phase as the decrease in lung function forced expiratory volume in one second 3-10 h aft er allergen inhalation, Asthma symptoms and drug use were monitored up to 1 8 h after allergen inhalation. The median nitrogen dioxide level during exposure was 313 mu g.m(-3) (range 203-462). The median levels of particles with 50% cut-off aerodynamic diam eters of 10 (PM10) and 2.5 mu m (PM2.5) were 170 (range 103-613) and 95 (ra nge 61-218) mu g.m(-3) respectively. Subjective symptoms during tunnel expo sure were not pronounced. However, subjects exposed to tunnel NO2 Levels of greater than or equal to 300 mu g.m(-3) had a significantly greater early reaction, following allergen exposure, as well as lower lung function and m ore asthma symptoms during the late phase, compared to control. Also, subje cts with PM2.5 exposure greater than or equal to 100 mu g.m(-3) had a sligh tly increased early reaction compared to control. In conclusion, exposure to air pollution in road tunnels may significantly enhance asthmatic reactions to subsequently inhaled allergens.