FIG. 2.

In vitro and in vivo dose comparison: ¹⁸O incorporation into bronchial brush biopsies collected from human subjects exposed for 2 h to 0.3 ppm ¹⁸O₃ while exercising intermittently or human primary epithelial cells exposed in vitro to a range of ¹⁸O₃ concentrations (mean ± SE). Standard error bars are within the data point for the in vivo data (N = 10 human subjects for in vivo data and 5 culture wells derived from two replicate in vitro exposures to each ¹⁸O₃ concentration for in vitro data). Each mean shown is significantly elevated (* denotes p < 0.05) relative to natural background ¹⁸O (zero ¹⁸O₃).