E-cigarette vapour composition is influenced by a number of factors. Some of which relate to the device physically (battery charge, wattage/temperature control, puffing profile) and others to the e-liquid itself (proportion of propylene glycol and glycerol, amount of nicotine, pH of solution). Standardizing how we study these devices will be key to understanding their impact.
Deposition is dependent on a multitude of factors such as particle size, physiochemical properties of the compound (hydrophobic vs hydrophilic), delivery route (IV vs IT vs aerosol), species, strain, and disease model.
To illustrate the relationship between inhaled particle size and deposition, find below graph from Patton and Byron Nature Reviews Drug Discovery (2007)1 showing that the respirable range is in the <5um range:
Smaller particulates will have better suspension and follow the natural flow of airway geometry to infiltrate further into the lungs. On the other hand, larger particles are heavier and tend to get deposited in the upper and central airways. Deposition is also dependent on species and strain and may vary with disease state.
The recent publication by Lechasseur et al.2 investigates the main variables in e-cigarette aerosolization that may affect particle size and ultimately distribution in the lungs such as:
Temperature-control mode is often promoted by e-cigarette companies as a way to maximize flavour and prevent overheating and coil degradation. Internal tests at SCIREQ show that temperature control mode allows the temperature to be kept constant by adapting power to coil and using resistance as feedback. The power-controlled modes tend to increase temperature over time to sustain a stable power target.
NOTE: Increasing temperatures change the density of e-cigarette smoke produced and the chemical composition.
In Lechasseur et al2 each mode is tested using a consistent ratio of 50% Propylene Glycol, 50% Vegetable Glycerine. They show that increasing power leads to an increase in particle size generated. In contrast, increasing temperature to its highest setting (250oC) yields the smallest particle size.
E-cigarette liquid mixtures mainly consist of varying percentages of vegetable glycerin (VG), propylene glycol (PG), and nicotine combined with a flavouring of choice. Unfortunately, manufacturing of e-liquids is highly unregulated. There are no standards set for consistency and as such, market e-liquid’s composition vary greatly from batch to batch.
The next step in the Dr. Lechasseur’s experiment is to assess the ratios of PV/VG under constant temperature conditions, in this case 210oC. When increasing the proportion of vegetable glycerine, the particle sizes also increase. This is done in absence of nicotine; however the addition of nicotine also increased the particle size.
E-cigarette liquids come in a variety a flavouring which make them more palatable and marketable to a larger target audience including adolescents. Many studies have shown that the flavours using in e-cigarette liquids have adverse health effects including pulmonary inflammation and oxidative stress (Gerloff et al. 20173, Rahman et al. 20184).
Lechasseur et al2 focused on three main flavourings in this study; specifically vanillin, menthol and matltol, showing that Vanillin significantly increased the particle size while the other flavours did not.
In conclusion, altering the e-cigarette modes (Power/temperature), e-liquid composition and flavouring can impact particle size and distribution, ultimately affect deposition. It is important to take this into consideration when designing an experiment and when reviewing the published literature.
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