Electronic nicotine delivery systems (ENDS) aerosol constituent deposition and nicotine retention in the human oral cavity

Measurement of the dynamics and deposition of electronic nicotine delivery systems (ENDS) aerosols in the human oral cavity is challenging due to thermodynamic instabilities of the puff. We developed a mathematical model to predict ENDS aerosol puff mixture deposition and uptake in the oral cavity based on physical and physiological parameters, such as droplet/vapor phase change, coagulation, heat exchange between the puff and oral cavity, and puffing maneuver. We refined previous modeling efforts by incorporating improved assumptions for droplet growth, humidity evaluation, and temperature-dependent parameters to predict droplet deposition and vapor component uptake. We predicted dosimetry during puff withdrawal and mouth-hold of puff constituents that are present in droplets or vapor. These included water, nicotine, propylene glycol (PG), vegetable glycerin (VG), and two flavor chemicals (vanillin and benzaldehyde) which are representative of flavor chemicals with low and medium vapor pressures that undergo phase change at different rates. Model predictions indicated low droplet deposition (<2%) of the humectants PG and VG; PG vapor exhibited higher vapor uptake (∼14%). Deposition of nicotine in droplet form was low (<2%). Retention of nicotine in vapor form was sensitive to the nicotine activity coefficient and was predicted to be as high as 30%. Flavor chemical uptake was dependent on vapor pressure, with vanillin exhibiting negligible uptake and benzaldehyde exhibiting significant uptake (∼45%). ENDS constituent-specific dosimetry predictions in the oral cavity can inform an evaluation of the amounts entering the lungs and predict ENDS constituent levels associated with potential upper respiratory adverse effects. The dosimetry models presented here demonstrate their value as a practical tool for use by regulatory agencies and the risk assessment community to assess potential health impacts to ENDS users.