A group of researchers funded by the Research Institute for Fragrance Materials (RIFM) have developed a new model for vapor deposition in the lung and have published their work in an article titled “Derivation of Mass Transfer Coefficients for Transient Uptake and Tissue Disposition of Soluble and Reactive Vapors in Lung Airways,” published in the June 2011 issue of the Annals of Biomedical Engineering. The authors represent a number of different organizations, including RIFM, the Hamner Institutes, the University of North Carolina, and Applied Research Associates.
According to the authors, the new model is intended to improve on earlier models of lung vapor uptake that “assumed steady state, one-way transport into tissues with first-order clearance,” and they propose an unsteady model that takes a “new approach to calculating lung dosimetry . . . in which an overall mass transfer coefficient for vapor transport across the air-tissue interface is derived using air-phase mass transfer coefficients and analytical expressions for tissue-phase mass transfer coefficients describing unsteady transport by diffusion, first-order, and saturable pathways.”
The study used mechanistic lung models with formaldehyde as a model vapor, though the authors say that the model is “equally applicable to other soluble and reactive compounds.” The model takes into account both absorption of the compound into airway tissue during inhalation and desorption during exhalation. In their conclusion, the authors note that steady state models overestimate accumulation of the compound in airway tissue and other organs and and therefore “may overestimate the associated health risk.”
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