ABSTRACT
To investigate whether intersubject variations in the dose of inhaled ozone (O(3)) cause corresponding variations in the physiological response, 28 female and 32 male nonsmokers participated in a 1-h continuous inhalation of clean air or 0.25 ppm O(3) while exercising on a cycle ergometer at a constant ventilation rate of 30 L/min. The exposure protocols included continuous monitoring of respiratory flow rate and O(3) concentration from which O(3) uptake (OZU) and fractional uptake efficiency (UE) were computed. Pre-to-post changes in forced expired volume in 1 s (%DeltaFEV(1)), peripheral cross section for carbon dioxide diffusion (%Delta A(P)), and Fowler dead space volume (V(D)) were also measured for each exposure. Individual values of UE ranged from .70 to .98 among all the subjects, with significant differences (p<.05) existing between men and women. These intersubject differences were inversely correlated with breathing frequency and directly correlated with tidal volume. The mean +/- SD values of %Delta FEV(1), %Delta A(P), and %Delta V(D) were all significantly more negative in the O(3) exposure session (-13.31 +/- 13.40, -8.14 +/- 7.62, and -4.20 +/- 5.12, respectively) than in the air exposure session (-0.06 +/- 4.56, 0.22 +/- 10.82, and -0.70 +/- 6.88, respectively). Finally, our results showed that neither %DeltaFEV(1) nor %Delta V(D) was correlated OZU, whereas there was a significant relationship (rho = -0.325, p = .0257) between %Delta A(P) and OZU. We conclude that the overall uptake of O(3) is a weak predictor of intersubject variations in distal airspace response, but is not a predictor of intersubject variations in conducting airway responses.
