Dr James Ultman and colleagues at Pennsylvania State University recruited 32 men and 28 women to examine differences in ozone uptake in the lung. The subjects (all non smokers) first took a series of single breaths of air–ozone mixtures, which allowed the investigators to examine how ozone was distributed in the airways and where the major fraction of ozone was taken up. In a follow-up test, the subjects pedaled a bicycle ergometer to produce conditions of moderate exercise for one hour while breathing clean air, followed by a third test while breathing ozone at 0.25 ppm). The investigators characterized the subjects' lung anatomy, average tidal volume, breathing frequency, and ozone uptake rate and efficiency. Before each exposure and 10 and 70 minutes afterward, they measured standard parameters of lung function, including FEV1 (forced expiratory volume in 1 second) and AP, a novel measure of bronchial cross-sectional area available for gas diffusion.