Longitudinal distribution of ozone absorption in the lung: quiet respiration in healthy subjects

The objective of this research was to develop a bolus-response method for the noninvasive determination of O3 distribution in the human lung. A previously developed O3 analyzer and bolus generator were incorporated in a computer-controlled inhalation system, and measurements of O3 absorption from inhaled 10-ml boluses with a peak O3 concentration of 4 ppm were carried out on nine previously unexposed healthy male subjects engaged in quiet oral breathing. The fraction of O3 absorbed during a single breath was measured over a range of airway penetrations from 20 to 200 ml, with inspiratory and expiratory flows fixed at a nominal value of 250 ml/s. The resulting data indicated that 50% of the inhaled O3 was absorbed at a penetration of 70 ml, which roughly corresponds to the upper airways, and essentially complete absorption occurred at a penetration of 180 ml, which roughly corresponds to the 16th airway generation, the beginning of the proximal alveolar region. This compares favorably with the results of direct-sampling methods, which indicated that 40.4% of continuously inhaled O3 is removed by the extrathoracic airways (Gerrity et al. J. Appl. Physiol. 65: 393-400, 1988). The computation of an absorption rate constant, Ka, revealed that the efficiency of O3 uptake increased with longitudinal position throughout most of the conducting airways but began to fall off at a penetration of 160 ml.