ASTHMATIC BRONCHIAL HYPERRESPONSIVENESS VARIES WITH AMBIENT LEVELS OFSUMMERTIME AIR-POLLUTION

It is widely believed that the mechanisms of action of outdoor air pol lutants are the same as those found in the laboratory, although few st udies have attempted to clarify this issue, This study investigates th e relationship of asthmatic bronchial hyperresponsiveness (BHR), a mar ker of airway inflammation, and pulmonary function to ambient levels o f summertime air pollution. Thirty eight nonsmoking adult asthmatic su bjects underwent repeated measurement of methacholine BHR, using Yan's method, at differing levels of air pollution (O-3, SO2, NO2, smoke) d uring summer 1993. A total of 109 evaluable tests were performed: 31 s ubjects completed three or more challenge tests, and seven managed two , Levels of all pollutants remained within current World Health Organi zation (WHO) Guidelines for Health, Changes in BHR were found to corre late significantly with changes in the levels of 24 h mean SO2, NO2 an d smoke; 48 h mean NO2 and smoke; 24 h lag NO2; although the effect wa s only small, accounting for approximately 10% of the variability in w ithin-subject BHR between visits, Twenty four hour lag NO2 was also as sociated with forced vital capacity (FVC). In conclusion, in subjects with asthma, methacholine bronchial hyperresponsiveness varies with am bient levels of summertime air pollution, This suggests that changes i n airway inflammation underlie the increased respiratory morbidity kno wn to accompany pollution episodes.