Predicted Deposition of E-Cigarette Aerosol in the Human Lungs

Background: Health effects of inhaling aerosol produced by electronic cigarettes (ECs) are still uncertain. This work analyzes ECs as specific inhalation devices, which can be characterized by aerodynamic resistance, size distribution of released droplets, and predicted regional and total lung deposition as a function of inhalation maneuver. Methods: The internal resistance of two types of EC and a conventional cigarette was evaluated by measuring ΔP-Q curves. Particle size distribution in EC-emitted mist was determined by laser diffraction. The measured data were used to calculate lung deposition based on two approaches: multipath particle dosimetry model (MPPD) and Finlay-Martin correlations. Computations were done for the set of ventilation parameters of an EC user, and also for a by-stander. Results: Tested ECs had higher aerodynamic resistance (1.6–1.9 mbar0.5 min/L) than tobacco cigarette (0.56 mbar0.5 min/L), and these values are much above the high-resistant DPIs. The average mass median diameter of droplets emitted from ECs was 410 nm, with the average GSD = 1.6. Predicted total lung deposition of the mainstream aerosol was 15%–45% depending on the breathing scheme. An expected increase of particle size in the exhaled aerosol led to predictions of 15%–30% deposition efficiency during passive vaping. Conclusions: ECs are characterized by high inhalatory resistance, so they require stronger physical effort to transfer cloud of droplets to the lungs, as compared, for example, to DPIs. A significant amount of aerosol is then exhaled, forming an unintentional source of particles to which by-standers are exposed. From this perspective, ECs are not optimal personal aerosol delivery devices.