Longitudinal distribution of ozone absorption in the lung: Effects of nitrogen dioxide, sulfur dioxide, and ozone exposures

Investigators used an ozone bolus inhalation method to study the effects of continuous exposure to ozone, nitrogen dioxide, and sulfur dioxide on ozone absorption in the conducting airways of human lungs. Healthy, young nonsmokers (6 males, 6 females) were exposed on separate days for 2 h to air containing 0.36 ppm nitrogen dioxide, 0.75 ppm nitrogen dioxide, 0.36 ppm sulfur dioxide, or 0.36 ppm ozone. Every 30 min, the subject interrupted exposure for approximately 5 min, during which he or she orally inhaled five ozone boluses—each in a separate breath. Investigators targeted penetration of the boluses distal to the lips in the 70–130-ml range, which corresponded to the lower conducting airways. The authors computed the change in absorption resulting from exposure (ΔΔ) by comparing the amount of each ozone bolus that was absorbed with a corresponding value obtained prior to exposure. Results indicated that ozone exposure caused ΔΔ to decrease relative to air exposure (p <.01), whereas both nitrogen dioxide and sulfur dioxide exposures caused an increase in ΔΔ that was not significantly different from air exposure. This resulted, at least in part, to an artifact caused by preexposure to ozone boluses. The authors concluded that exposure of the lower conducting airways to nitrogen dioxide or sulfur dioxide increased their capacity to absorb ozone because more of the biochemical substrates that are normally oxidized by ozone were made available. During continuous ozone exposure, this excess of substrate is depleted and the absorption of ozone boluses decreases.