Results: The mean values of peak expiratory flow were 346.0 L/min, 399.3 L/min, and 364.1 L/min over the three study periods. Peak expiratory flow levels increased in 78% of the participants when comparing the during- with pre- Olympics time points, while peak expiratory flow levels decreased in 80% of participants for the post- and during-Olympic periods comparison. In subgroup analyses comparing the during-Olympic to pre-Olympic time points, we found a larger percentage change in peak expiratory flow ( þ 17%) among female, younger and non-smoking participants than among male, elderly and smoking participants ( þ 12%). The percentage of participants with a fast breath rate ( 4 20/min) changed from 9.7% to 4.9% to 30.1% among females, and from 7.9% to 2.6% to 27.3% among males over the three time points. The changes in blood pressure over the three study periods were not very clear, although there is an increase in diastolic pressure and a decrease in pulse pressure among males during the games. Conclusions: The results suggest that exposure to different air pollution levels has significant effects on respiratory function. Smoking, age and gender appear to modify participants' biological response to
changes in air quality.