Description of acute ozone response as a function of exposure rate and total inhaled dose

The magnitude of respiratory responses to short-term ozone exposure is known to be a function of the exposure variables concentration (C), duration of exposure (T), and minute ventilation (VE) during exposure. The purpose of this study was to identify a mathematical model that described ozone-induced mean decrements in forced expiratory volume in 1 s (FEV1) as a function of exposure rate (C x VE) and total inhaled dose (C x VE x T). Three hundred seventy-four young male nonsmokers participated in 504 exposures to several concentrations of ozone for 2 or 6.6 h. Mean percent change in FEV1 was calculated for each hour of exposure and was fit to the exposure variables by use of nonlinear models. We identified a general sigmoid-shaped model that well described the observed mean response in terms of exposure rate and total inhaled dose over a wide range of C and T. By fixing the value of a single parameter, this model reduces to a simpler form, which was adequate for description of responses over narrower ranges of exposure conditions. We concluded that the observed mean responses to short-term ozone exposure were adequately described by the nonlinear models identified in this study and that models of this form may be useful for description of responses over a wide range of C and T.