Longitudinal distribution of ozone absorption in the lung: comparison of nasal and oral quiet breathing

Employing a bolus inhalation system, we noninvasively measured the fraction of inhaled ozone (O3) that is absorbed during a single breath (lambda) as a function of bolus penetration volume into the respiratory tract (Vp). During nasal breathing at a constant respiratory flow of 250 ml/s, lambda increased smoothly as Vp increased with 80% of the inhaled O3 absorbed in the upper airways and 90% absorbed at the distal end of the trachea. Oral breathing caused a distal shift of the lambda-Vp distribution to the extent that absorption in the upper airways was reduced to 50% and inhaled O3 was 90% absorbed only after a bolus reached the 13th bronchial generation. Therefore, an exercise-induced change from nasal to oral breathing can render the distal lung more susceptible to O3 damage because of an elevation in O3 dose. We also found that changing the peak inhaled bolus concentration over a 10-fold range of 0.4–4 ppm O3 did not affect the lambda-Vp distribution. This finding implies that the diffusion and chemical reaction dynamics that dictate O3 absorption are linear processes.