Assessment of Human Exposure to Gaseous Pollutants

A mathematical model to aid in assessment of human environmental exposure to volatile organic substances is presented. The model simulates the convective and diffusive transport of gas from the ambient environment into the human body by way of the respiratory and circulatory systems. Data required include easily obtained physical and chemical properties of substances as well as several estimated or measured physiological parameters. Transient and steady‐state tissue concentrations resulting from an input atmospheric partial pressure are predicted. From these concentrations, an effective dose may be calculated, allowing for the determination of an exposure‐response relationship based upon independently obtained dose‐response data. The model's results compare favorably to experimental data on oxygen and halothane. Steady‐state conditions are reached very rapidly. These results suggest that uptake of these substances is limited by both ventilation and perfusion. The sensitivities of steady‐state concentrations to changes in the ventilation and perfusion rates are demonstrated to be essentially linear within the current neighborhoods. Conditions in which the primary processes of ventilation, diffusion, perfusion, and elimination limit uptake of gases are considered. Expressions describing the conditions necessary for a single process to limit gas uptake are derived. Accompanying equations for estimating tissue concentrations under these limiting conditions are presented.