Effect of short-term NO2 exposure on induced sputum in normal, asthmatic and COPD subjects

The aim of this study was to assess the effects of short-term exposure to low levels of nitrogen dioxide (NO2) on airway inflammation. We studied seven normal, eight mild asthmatic and seven chronic obstructive pulmonary disease (COPD) subjects. All subjects were exposed to air or to 0.3 parts per million (ppm) NO2 for 1 h, with moderate intermittent exercise, on different days and in random order. Before and 2 h after exposure, symptom score and results of pulmonary function tests (PFTs) were assessed. All subjects performed nasal lavage and hypertonic saline (HS) inhalation to collect sputum 2 h after both exposures. Asthmatic subjects had a higher percentage of eosinophils than normal and COPD subjects in HS-induced sputum after air (asthmatics: median 13 (range 0.4-37)%; normals: 0 (range 0-2)%; COPD 1.8 (range 0.1-19)%), whilst COPD patients showed a higher percentage of neutrophils than the two others groups. No significant differences in PFT values or percentages of inflammatory cells were observed in nasal lavage and in HS-induced sputum in normal, asthmatic and COPD subjects after NO2 exposure compared to air exposure, except for a mild decrease in forced expiratory volume in one second (FEV1) 2 h after NO2 exposure in COPD patients. Symptom score showed a mild increase after NO2 exposure both in normal subjects and in COPD patients. We conclude that short-term exposure to 0.3 ppm nitrogen dioxide does not induce an early detectable acute inflammation in proximal airways of normal subjects or of patients with asthma or chronic obstructive pulmonary disease.