Comparative inhalation exposure/toxicology analysis of e-cigarette vapors with different puffing behaviors using PBPK-CSP-CFD approach

The overarching purpose of this study is to develop a numerical prediction method for assessment of human health risks caused from the inhalation exposure of various contaminants generated by electronic cigarettes (e-cigarettes). In this study, the inhalation exposure to contaminants, generated from e-cigarette smoking under two types of puffing behaviours was quantitatively estimated adapting a coupled physiologically based pharmacokinetic (PBPK)-computational fluid dynamics (CFD) model to a numerical respiratory tract model. Heterogeneous contaminants concentration distributions inside the respiratory tract were predicted through transient CFD simulations. For evaluating adsorption flux onto respiratory tissue surface, tissue surface contaminants concentrations of respiratory tract were calculated by using two concepts: partition coefficient between air-phase and tissue-phase and analogy of flux conservation. Contaminants concentration distributions inside the tissue were analyzed by using PBPK model. Through the coupled PBPK-CFD analyses, we indicated total fractions of contaminants inhaled from e-cigarette: (i) adsorbed onto tissue surface of respiratory tract, (ii) transported to deeper bronchial regions, and (iii) released into the indoor environment by exhalation. Basically, we indicated total respiratory uptake as a health risk factor of e-cigarette user and total amount of chemicals released into the indoor environment by exhalation as data which enable us to analyze second-hand and third-hand effects against non-user and indoor air quality.