Effects of 0.2 ppm nitrogen dioxide on pulmonary function and response to bronchoprovocation in asthmatics

Abstract

To study the respiratory effects of nitrogen dioxide (NO ₂ ) at ambient concentrations, we exposed 31 asthmatic volunteers to purified air (control) and to 0.2 ppm NO ₂ for 2‐h periods with light intermittent exercise. Bronchial reactivity (loss of forced expiratory performance in response to graded doses of methacholine chloride aerosol) was determined postexposure, using a newly developed apparatus that allowed accurate quantitation of methacholine dose. Forced expiratory performance, total respiratory resistance, and symptoms were also recorded immediately pre‐ and postexposure (prior to methacholine challenges). No significant direct effect of NO ₂ exposure on forced expiratory function or total respiratory resistance was observed. Symptoms showed a small significant (p ₂ exposures. Individual responses to methacholine varied greatly. About two‐thirds of the subjects showed greater response after NO ₂ than after purified air, but the mean excess response was small. Mean changes attained significance in some but not all applicable statistical tests. Thus we cannot conclude unequivocally that NO ₂ exposure increased bronchial reactivity in this group, although there was some tendency in that direction.