Noninvasive determination of respiratory ozone absorption: the bolus-response method

Morphometric studies in animals exposed to ozone (O3), and mathematical simulations of O3 transport in human lungs indicate that O3 toxicity is focal in nature, causing tissue damage that is more pronounced in the proximal alveolar region (the proximal end of the respiratory airspaces in our compartment models) than in other airways. These findings suggest that the internal distribution of O3 uptake must be known in order to assess health risk reliably. In previous work (Ultman and Ben-Jebria 1990), we developed a fast-responding chemiluminescent O3 analyzer and a small-scale O3 generator, both of which are suitable for respiratory measurements. The objective of the current research was to integrate these instruments into a bolus inhalation system capable of noninvasively measuring the longitudinal distribution of O3 absorption in intact human lungs. With this system we aimed to carry out baseline experiments in healthy men during quiet oral breathing at a respiratory flow rate of 250 mL/sec, determine the effect of alternative respiratory flow rates between 150 and 1,000 mL/sec, compare the absorption distribution during quiet oral breathing with that during quiet nasal breathing, and ascertain the influence of a peak inspired concentration between 0.3 and 4.0 parts per million (ppm). Ozone uptake (lambda) was expressed as the amount of O3 absorbed during a single breath relative to the amount in the inhaled bolus. Measurements of lambda were correlated with the penetration volume (VP) of the bolus into the respiratory tract. Values of VP less than 70 mL were considered to be associated with the upper airways, values between 70 and 180 mL were associated with the lower conducting airways, and values greater than 180 mL were associated with the respiratory airspaces. During quiet oral breathing, lambda increased smoothly with VP, with 50% of the inhaled O3 absorbed in the upper airways and the balance absorbed within the lower conducting airways. This compares favorably with the results of direct-sampling methods, which have indicated that 40.4% of continuously inhaled O3 is removed by the extrathoracic airways (Gerrity et al. 1988). The effect of increasing the respiratory flow, which occurs when people exercise, was to shift the lambda-VP distribution distally so that significantly less O3 was absorbed in the upper airways and more reached the respiratory airspaces. Compared with oral breathing, nasal breathing caused a proximal shift in the lambda-VP distribution to the extent that absorption in the upper airways increased from 50% to 80%.(ABSTRACT TRUNCATED AT 400 WORDS)