Ozone uptake in the intact human respiratory tract: relationship between inhaled dose and actual dose

Inhaled concentration (C), minute volume (MV), and exposure duration (T) ar e factors that may affect the uptake of ozone (O-3) within the respiratory tract. Ten healthy adult nonsmokers participated in four sessions, inhaling 0.2 or 0.4 ppm O-3 through an oral mask while exercising continuously to e licit a MV of 20 l/min for 60 min or 40 l/min for 30 min. In each session, fractional absorption (FA) was determined on a breath-by-breath basis as th e ratio of O-3 uptake to the inhaled O-3 dose. The mean +/- SD value of FA for all breaths was 0.86 +/- 0.06. Although C, MV, and T all had statistica lly significant effects on FA (P < 0.0001, P = 0.004, and P = 0.026, respec tively), the magnitudes of these effects were small compared with intersubj ect variability. For an average subject, a 0.05 change in FA would require that C change by 1.3 ppm, MV change by 46 l/min, or T change by 1.7 h. It i s concluded that inhaled dose is a reasonable surrogate for the actual dose delivered to a particular subject during O-3 exposures of <2 h, but it is not a reasonable surrogate when comparisons are made between individuals.