A lung dosimetry model of vapor uptake and tissue disposition
Abstract
Inhaled vapors may be absorbed at the alveolar-capillary membrane and enter arterial blood flow to be carried to other organs of the body. Thus, the biological effects of inhaled vapors depend on vapor uptake in the lung and distribution to the rest of the body. A mechanistic model of vapor uptake in the human lung and surrounding tissues was developed for soluble and reactive vapors during a single breath. Lung uptake and tissue disposition of inhaled formaldehyde, acrolein, and acetaldehyde were simulated for different solubilities and reactivities. Formaldehyde, a highly reactive and soluble vapor, was estimated to be taken up by the tissues in the upper tracheobronchial airways with shallow penetration into the lung. Vapors with moderate solubility such as acrolein and acetaldehyde were estimated to penetrate deeper into the lung, reaching the alveolar region where absorbed vapors had a much higher probability of passing through the thin alveolar-capillary membrane to reach the blood. For all vapors, tissue concentration reached its maximum at the end of inhalation at the air-tissue interface. The depth of peak concentration moved within the tissue layer due to vapor desorption during exhalation. The proposed vapor uptake model offers a mechanistic approach for calculations of lung vapor uptake, air:tissue flux, and tissue concentration profiles within the respiratory tract that can be correlated to local biological response in the lung. In addition, the uptake model provides the necessary input for pharmacokinetic models of inhaled chemicals in the body, thus reducing the need for estimating requisite parameters.