Asthmatic bronchial hyperresponsiveness varies with ambient levels of summertime air pollution.

It is widely believed that the mechanisms of action of outdoor air pollutants are the same as those found in the laboratory, although few studies have attempted to clarify this issue.This study investigates the relationship of asthmatic bronchialhyperresponsiveness (BHR), a marker of airway inflammation, and pulmonaryfunction to ambient levels of summertime air pollution. Thirty eightnonsmoking adult asthmatic subjects underwent repeated measurement ofmethacholine BHR, using Yan's method, at differing levels of air pollution(O3, SO2, NO2, smoke) during summer 1993. A total of 109 evaluable testswere performed: 31 subjects completed three or more challenge tests, andseven managed two. Levels of all pollutants remained within current WorldHealth Organization (WHO) Guidelines for Health. Changes in BHR were foundto correlate significantly with changes in the levels of 24 h mean SO2,NO2 and smoke; 48 h mean NO2 and smoke; 24 h lag NO2; although the effectwas only small, accounting for approximately 10% of the variability inwithin-subject BHR between visits. Twenty four hour lag NO2 was alsoassociated with forced vital capacity (FVC). In conclusion, in subjectswith asthma, methacholine bronchial hyperresponsiveness varies withambient levels of summertime air pollution. This suggests that changes inairway inflammation underlie the increased respiratory morbidity known toaccompany pollution episodes.