Effects of Exposure to 4 PPM Nitrogen Dioxide in Healthy and Asthmatic Volunteers

ABSTRACT

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 < .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 < .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.