Effects of exposure to 4 ppm nitrogen dioxide in healthy and asthmatic volunteers

Healthy and asthmatic volunteer subjects (N = 25 and N = 23, respectively) were exposed twice each to purified air (control) and to 4 ppm nitrogen dioxide (NO2) in a controlled-environment chamber. Exposures lasted 75 min, and included 15 min each of light exercise (ventilation rate near 25 L/min) and heavy exercise (near 50 L/min). Compared to control, NO2 exposure produced no statistically significant untoward effects on airway resistance, symptoms, heart rate, skin conductance, or self-reported emotional state in normal or asthmatic subjects. Exercise was associated with significantly (P less than .001) increased airway resistance in both subject groups, although the increase in normals was small. In both groups, systolic blood pressure showed small but significant (P less than .01) decreases with NO2 exposure, compared to control. This effect, if real, may relate to formation of a vasodilating nitrite or nitrate from inhaled NO2. The lack of respiratory response contrasts with previous findings elsewhere; at present, this inconsistency is unexplained.