The relationship between delivered ozone dose and functional responses in humans.

The relationship between delivered ozone dose and variability of pulmonary function response to ozone was investigated in 20 young, healthy, nonsmoking male volunteers. The subjects were exposed to 0.4 ppm ozone for 1 hr during which time they walked on a treadmill at a speed and inclination sufficient to induce a minute ventilation (VE) of 20 liter/min/m2 body surface area. Prior to and immediately following exposure spirometric and plethysmographic measurements of lung function were made. In addition, 5 min after the beginning of exposure and 5 min before the end of exposure the uptake efficiency of ozone in the upper and lower respiratory tract, spontaneous tidal volume (Vt), and breathing frequency (f) were measured. During exposure subjects wore a noseclip in order to constrain breathing to the oral pathway. Uptake efficiencies in the upper (FURT) and lower (FLRT) respiratory tracts were determined by continuously drawing air from the posterior pharynx into a rapidly responding chemiluminescent ozone analyzer. Linear regression models were constructed to examine the relationships between pulmonary function and breathing pattern responses, and the instantaneous and average values of FLRT and VE. Initial VE and average VE (VE) were found to be significant predictors of FEV1 decrement (p = 0.011 and p = 0.006, respectively). In addition the cross-product term FLRT x VE was a significant predictor of Vt decrement (p = 0.02). These results suggest that delivered dose, as determined primarily by VE, is responsible for some of the intersubject variability of ozone response. The failure of FLRT to play a significant role may be due to the fact that it primarily reflects ozone uptake in the lung periphery distal to anatomical sites where the ozone response may be mediated.