Airway Responses to 2.0 ppm Nitrogen Dioxide in Normal Subjects

Abstract

Nitrogen dioxide (NO₂) is a common indoor air pollutant. To characterize the acute respiratory responses to this gas, 18 nonsmoking normal subjects (mean age ± standard deviation [SD] = 25 ± 4 yr) were exposed to filtered air or 2 ppm NO₂ gas for 1 hr in a 30-m³ environmental chamber on different days, typically 1 wk apart, in a double-blind randomized fashion. Lung function tests included forced vital capacity, forced expiratory volume in one second, partial expiratory flow at 40% of vital capacity (V_p40), functional residual capacity, and specific airway conductance, and were measured before and after exposure. Airway reactivity to methacholine inhalation was determined within 45 min of each exposure. The dose of methacholine in mg/ml to cause a 40% decrease in specific airway conductance (PD₄₀) was measured. Airway reactivity to methacholine aerosol increased significantly after NO₂, which is shown by a decrease in the concentration of methacholine; PD₄₀ (AIR) = 101 ± 44, PD₄₀ (NO₂) = 81 ± 45 mg/ml, p = .003. No significant changes were noted in the lung function tests after NO₂ exposure. These findings indicate that normal nonsmokers exposed to 2.0 ppm NO₂ for 1 hr develop an increase in airway reactivity to methacholine aerosol, which is not associated with changes in lung volumes, flow rates, or respiratory symptoms.