LONGITUDINAL DISTRIBUTION OF OZONE ABSORPTION IN THE LUNG - EFFECTS OF RESPIRATORY FLOW

In our previous work, we developed a bolus inhalation apparatus and measured the longitudinal distribution of ozone (O-3) uptake in intact human lungs at a quiet respiratory flow of 250 ml/min. The objective of the present study was to determine the effect of alternative respiratory flows between 150 and 1,000 ml/s. Uptake was expressed as the O-3 absorbed during a single breath relative to the amount of O-3 in the inhaled bolus (Lambda). Measurements of Lambda were correlated with the penetration volume of the bolus into the respiratory tract (Vp). Vp in the range of 20-70 ml was considered to indicate upper airways (UA), the Vp interval of 70-180 ml was identified as lower conducting airways (CA), and Vp > 180 ml was associated with the respiratory air spaces (RA). During quiet oral breathing at 250 ml/s, Lambda increased smoothly as Vp increased, with 50% of the inhaled O-3 absorbed in the UAs and the remainder absorbed within the CAs such that no O-3 reached the RAs. The effect of increasing the respiratory flow was to shift the Lambda-Vp distribution distally such that significantly less O-3 was absorbed in the UAs and CAs and some O-3 reached the RAs. For example, at 1,000 ml/s, only 10% of the inhaled O-3 was absorbed in UAs and 65% was absorbed in the CAs such that 25% reached the RAs. Further analysis of these data with a mathematical diffusion model suggested that the reaction between O-3 and biochemical substrates is so fast (i.e., estimated 1st-order rate constant was on the order of 10(6) s(-1)) that O-3 is decomposed close to the gas-mucus interface in the CAs.